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1. Before making any measurement you will have to enter information about the SPRT and reference resistor into the microK s database When the main window opens press the Jnstrument tab eS Page 19 of 117 Issue 1 05 Single Multi gt Instrument Channel T Gy Zero Power Value e Start Save Set Scales Uncertainty Rt Rs Clear Graph 0 0 Time f s In the Instrument tab press Edit Thermometers Single Multi Settings Instrument Edit Thermometers System Calibration x Edit Resistors Set Date and Time Calibration Backup Data Restart Software Clear Data Files Update Software Backup Configuration Change Password Load Configuration You will be prompted to enter the password set to 1234 initially but this should be changed before using the microK in a real measurement calibration application to ensure security see section 3 7 5 2 Enter the password to open the resistor database window Press New to create a new thermometer entry in the database and enter data by pressing the up down or ellipses buttons by each field Soe Page 20 of 117 Issue 1 05 tT ISPRT 1 o Thermometer Thermometer Type PRT Thermometer Name SPRT 1 Manufacturer s Name Min Temperature C Iso
2. None Ohms it 125 Reference Channel Channel 2 100 Reference Resistor EAE Readings in Rolling Statistics oe WILKINS 1 e Press the ellipses button by the Current mA box to open the Current window eves Page 15 of 117 Issue 1 05 1 0000 mA Custom imA 10mA x V2 IS Zero Power Extrapolation Clear Zero Power Extrapolatior OK Cancel Press the Zero Power Extrapolation button to open the current sequence 0 1mA 0 5mA Hid BER i window Settling Time s Normal Current mA Alternate Current mA Readings at Each Current Cancel Sequence This window allows you to define the measurement sequence used to calculate the zero power resistance The measurement sequence comprises a measurement at the normal current followed by a measurement at the alternate current and then a final measurement at the original normal current Before each measurement the microK waits for the defined settling time in order for the thermometer to come to thermal equilibrium following the change in current If the settling time for the thermometer is not known it can easily be determined by measuring its resistance at the fixed normal current and then manually Sore Page 16 of 117 Issue 1 05 changing
3. RATio REFerence REFerence RANGe UPPer RANGe UPPer INITiate IMMediate ALL FETCh SCALar READ SCALar MEASure SCALar lt function gt lt channel gt lt reference channel gt lt resistance range gt lt current gt lt denominator channel gt lt resistance range gt lt current gt VOLTage DC lt channel gt FRESistance lt channel gt REFerence lt reference gt lt resistance range gt lt current gt RATio lt channel gt REFerence SOURce CURRent TEST CURRent CALibrate CURRent REFerence lt reference gt REFerence lt reference gt OFFSet lt channel gt OFFSet lt channel gt GAIN GAIN GAIN RESet GPIB ADDRess GPIB ADDRess PASSword UNLock LOCK Sorsi lt resistance range gt lt current gt lt current gt lt current gt lt actual current gt lt actual resistance gt lt offset gt lt polarity gt lt adjustment gt lt polarity gt lt gpib address gt lt old password lt password gt lt password gt lt password gt Page 101 of 117 Issue 1 05 A detailed description of each command follows 11 6 5 Command IDN Format IDN Reports information on the microK in 4 comma separated fields manufacturer model serial number firmware version S S S amp Example for a microK 100 with serial number 09 P119 ITL261067 using firmware version 1 14 the microK responds to IDN with Isotherma
4. Sors Page 28 of 117 Issue 1 05 manual describes how to use microsKanner multiplexers with your microK bridge The start up window contains the Resume button Isothermal Technology microK 100 v1 4 4 S N 09 P119 firmware version 1 14 microsKanners detected none Resume Measurement system initialised Resume Pressing the Resume button places the microK in the state it was in prior to its last power down Before pressing Resume make sure that any thermometers attached will not be damaged by the sense currents that will be applied the last values used If there is a problem disconnect your sensors before proceeding and then reconnect them after changing the sense currents to the required value 3 3 The Main Window Having pressed Resume in the start up window the user is presented with the main window SYSE Page 29 of 117 Issue 1 05 single Multi Settings Instrument Channel p io Clear Graph 24 9998 Ohms 24 999794 Mean of last 100 e Start Save Set Scales 0 000009 SD Clear 24 9999500 24 9999000 24 9998500 24 9998000 Pera AA tel RN a D AA NS AEAN TAAS 24 9997500 24 9997000 24 9996500 24 9996000 50 100 150 200 250 300 Time f s All functions to control the microK are available in this window which is divided into four tabs Single displays a single channel in numer
5. Clear Data Files Backup Configuration Load Configuration You will be prompted to enter the password set to 1234 initially Enter the password to open the resistor database window Press New to create a new resistor entry in the database and enter data by pressing the ellipses button by each field tt WILKINS 1 g Resistor Resistor Name WILKINS 1 Manufacturer s Name Tinsley Serial Number 279509 Calibration Due 15 12 2008 New Delete value 99 999831 il Press OK to close the resistor window Connect the SPRT to channel 1 see section 4 2 for details on how to connect 4 wire PRTs and the reference resistor to channel 2 Press the Settings tab in the main window and disable channels 2 and 3 this will speed up measurements on channel 1 which we will be using by using the up down buttons by the Channel box to select these channels and pressing bors Page 22 of 117 Issue 1 05 Disable Use the up down buttons to return to channel 1 Use the up down or ellipses buttons by each box to select the required settings for the SPRT Single Multi Channel Settings Instrument Therrnometer GEE e Units Pec a Current mA tt SPRT 1 Conversion ITS90 Range Ohms 2 125 2 Refer
6. Deviation Function E Eref aT bT 2 cT 3 T inc E in pv 0 08569334 an 0 0001871873 p 9 183761E 08 c Press the Edit Resistors button to create edit or delete a reference resistor in the database You will be prompted to enter the password in order to proceed tt WILKINS 1 Resistor Name WILKINS 1 Manufacturer s Name Tinsley Serial Number 279509 Calibration Due 15 12 2008 E New Delete B g Resistor Value 99 999831 B Resistor box Use the up down buttons to select the reference resistor you wish to edit or delete Alternatively press the New key to create a new reference evred Page 42 of 117 Issue 1 05 resistor entry The internal reference resistors are included in the list but cannot be edited or deleted Resistor Name box This box contains the name of the selected reference resistor Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter a name The Shift key toggles the alpha keys between upper and lower case Manufacturer s Name box This box contains the manufacturer of the selected reference resistor Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter a name The Shift key toggles the alpha keys between upper and lower case Serial Number box This box contains the serial number of the selecte
7. The microK is unique in being able to sequence the current and generate a zero power corrected value including an uncertainty figure without using any external software This tutorial describes how to make a zero power corrected resistance measurement of an SPRT against an external reference resistor at a single temperature and logging all this information to files on a USB flash drive From start up press Resume to restart your microK Isothermal Technology microK 100 v1 4 4 S N 09 P119 firmware version 1 14 microsKanners detected none Resume Measurement system initialised SYSE Page 13 of 117 Issue 1 05 Before making any measurement you will have to enter information about the reference resistor into the microK s database When the main window opens press the Instrument tab Single Multi Instrument Channel 2 2 Ise Clear Graph Rt Rs zero Power Value e Start Save Set Scales Uncertainty Details HE 0 0 Time f s In the Instrument tab press Edit Resistors Single Multi Settings Instrument Edit Thermometers SEmi calaton x lt 5 Edit Resistors Set Date and Time Calibration Backup Data Restart Software Clear Data Files Update Software Backup Configuration Change Password Load Configuration You will be prompted to enter the password s
8. ensures that the input signal is balanced against the output of the DAC so that the average value of the 1 bit data stream from the DAC equals the input signal A low pass digital filter is then used to extract the converted value from the 1 bit data stream Another way of viewing the operation of a X A ADC is to consider what is happening in the frequency domain The over sampling used in 2 A converters means that the quantisation noise caused by the 1 bit ADC is spread over a wide bandwidth whereas the signal we are looking for is unaffected by this over sampling The digital filter selects the narrow bandwidth of the required signal The amount of quantisation noise in this bandwidth is relatively small because the over sampling spreads the noise power over such a large bandwidth The quantisation noise on the converted signal can be reduced by increasing the sampling rate but it becomes increasingly difficult to maintain performance as the clock rate of the system increases Another way to reduce the noise would be to use a multi bit ADC and DAC in the feedback loop This would not normally be feasible since the DAC would carry the full accuracy burden of the measurement system However by using a PWM Pulse Width Modulation DAC in which the output is a signal of fixed frequency and amplitude but variable pulse width we turn the problem of producing accurate voltage or current levels into one of accurate timing Whereas achieving sub p
9. suffices These are represented by a hash in the command notation for example MEASure VOLTage lt channel gt In addition to the 3 input channels on the front panel which are assigned the suffices 1 2 and 3 the internal reference resistors are specified using numeric suffices as follows channel Internal reference resistor 203 25 Q 204 100 Q 205 400 Q In order to measure the voltage on channel 3 the command used would be MEAS VOLT3 11 4 Parameters If a command requires parameter s these follow the command and are separated from it by a space If more than one parameter is required each parameter is separated by a comma For example the command to measure a four terminal resistance on channel against a reference resistor on channel 2 using the 100 ohm range and a sense current of 1mA would be MEAS FRES1 REF2 100 1 11 5 Units Numeric parameters may optionally include units The standard multiplying prefixes may also be used to indicate decimal multiples or fractions For example the following are all equivalent CURRENT 0 001A CURRENT Ima CURRENT 1000UA CURRENT 1 Sors Page 96 of 117 Issue 1 05 The following prefixes are available prefix name factor Norn nano 10 Uoru micro 10 M or m milli 10 Kork kilo 10 MA orma mega 10 Sors Page 97 of 117 Issue 1 05 11 6 Making Measurements using SCPI Commands The microK s measurement system is controlled b
10. 3 wire PRTs although it will not automatically compensate for cable resistance The two red terminals should be connected together and then connected to the single end of the 3 wire PRT as follows The connection to the single end of the 3 wire PRT should be short have a low resistance in order to minimise the effect of lead resistance on the measurement Alternatively the connection to the single end can use remote sensing using the 4 wire measurement capability of the microK to eliminate the effect of its lead resistance In this arrangement the current and voltage sense connections to the single end are only joined close to the PRT v The top terminal should be connected to the screen of the PRT s lead to minimise electrical noise picked up by the wires Soreth Page 53 of 117 Issue 1 05 4 4 Connecting PRTs 2 wire The microK can be connected to 2 wire PRTs The two red and two black measurement terminals should be connected together and then connected to the PRT as follows V The connections to the PRT should be short low resistance in order to minimise the effect of lead resistance on the measurement Alternatively the connections can use remote sensing using the 4 wire measurement capability of the microK to eliminate the effect of lead resistance completely In this arrangement the current and voltage sense connections are kept separate and are only joined clos
11. 5Q SPRT up to a maximum resistance of 30Q against the internal 100Q reference the maximum resistance that the measurement system sees is 100Q To make this measurement using a lmA sense current you can use the following command sequence SENS FUNC FRES CURR 1 SENS FRES RANG 100 1 Suissa Page 98 of 117 Issue 1 05 SENS CHAN 1 SENS FRES REF 204 READ The microK will then report the measured resistance for example 2 5250637862E001 The following command performs the same measurement MEAS FRES1 REF204 100 1 11 6 2 Measuring Voltage using SCPI Commands In order to measure the voltage from a thermocouple you need to set the microK to measure voltage select the measurement channel make the measurement If you want to measure the voltage from a thermocouple you can use the following command sequence SENS FUNC VOLT SENS CHAN 1 READ The microK will then report the measured voltage for example 1 12999999E 007 The following command performs the same measurement MEAS VOLT1 11 6 3 Measuring Temperature using SCPI Commands In order to measure temperature you need to make one of the base unit measurements resistance or ratio for PRTs resistance for thermistors or voltage for thermocouples and then convert this into a temperature using a conversion algorithm for example ITS 90 for an SPRT The data for the conversion temperature algorithms is stored in a database accessed fro
12. Ceh Reference Resistor qg Ej Channel box Use the up down buttons to select the channel you wish to configure Alternatively press the ellipses button to open a numeric entry window and select the channel directly The ellipses button is particularly useful when the microK is used with microsKanner multiplexers which can provide up to 90 expansion channels Enable Disable button Use this button to enable or disable a channel Disable unused channels to skip measurements on that channel and reduce the cycle time through the channels The nearby indicator shows whether the currently selected channel is enabled Thermometer box Use the up down buttons to select the required thermometer Initially this box will contain only default PRT Thermocouple or Thermistor You can use these entries for uncalibrated thermometer sensors If you add thermometers to the microK s Thermometer Database see section 3 7 1 these will also appear in the list within this box Sorsi Page 35 of 117 Issue 1 05 Conversion box If the selected thermometer is one of the default types you can use the up down buttons to select a standard polynomial function for converting the thermometer s base measurement to temperature If the selected thermometer is one that your have created in the Thermometer Database this box will be fixed and will be the conversion type defined for that thermometer Range
13. Page 47 of 117 Issue 1 05 If a file with the same name is already present on the USB flash drive you will be asked whether you wish to over write it To proceed you will need to enter the password Files are transferred to the USB flash drive in directory microKData serialnumber data where serialnumber is the serial number of the microK used to make the measurements This means that you can have duplicate filenames for measurements provided they are made with different instruments The measurements are written to the file in comma delimited ASCII text form allowing easy importation into Microsoft Excel or other applications 3 7 10 Clear Data Files Press Clear Data Files to delete the data files from the internal memory this frees up space for new files to be recorded You will be prompted to enter the password before proceeding Unless you are sure that you do not need any of the files in the internal memory you should transfer all files from the internal memory to a USB flash drive see section 3 7 9 before using this feature 3 7 11 Backup Configuration Press Backup Configuration to save the current configuration settings of the microK You will be prompted to enter the password before proceeding You will then be offered the choice buttons of storing the configuration to the Internal memory solid state drive or an External USB flash drive Press the required button to open an Alpha Numeric Keybo
14. RD 3 TD 4 DTR 5 SG 6 DSR 7 RTS 8 CTS 9 FG Function carrier detect not connected receive data transmit data data terminal ready fixed high signal ground data set ready not connected request to send clear to send not used not connected frame ground screen Connect your microK to a PC using a standard null modem cable T ooNOoOJNAOUON OANOAKRWND Shell no gt 2 Null Modem Cable The format for the RS232 interface is as follows Baud Rate 9 600 Start Bits 1 Stop Bits 1 Parity Bit none Sorsi Page 89 of 117 Issue 1 05 The microK has a 254 byte circular receive buffer If the buffer becomes full it de asserts RTS connected to CTS on your PC through the null modem cable to prevent further data being sent If the PC continues to send data this will be ignored lost until the microK has had time to make space in the buffer by processing commands The microK does not use its CTS to control data it transmits You can use Hyperterminal or another terminal emulator to communicate with the microK via the RS232 connection Hyperterminal is part of the standard Windows installation usually located in the Accessories Communications folder If you have installed a minimum laptop or custom configuration without this component for your Windows operating system you may need to install Hyperterminal from your original Windows media Start Hyperterminal to setup a new connec
15. This technique is less accurate than using an ice point or water triple point due to the additional uncertainties associated with the PRT used to monitor the Sors Page 55 of 117 Issue 1 05 reference junction and any temperature gradients that result in a difference between the temperature of the PRT and the reference junction 4 7 Connecting Thermistors The microK can be connected to thermistors using the same arrangement as for 2 wire PRTs see section 4 4 THERMISTOR V Because the resistance of thermistors used for temperature measurement is much higher than for PRTs lead resistance is not normally a problem Use an external reference resistor with thermistors since the resistance of the internal standards is too low Ideally the value of the reference resistor should be similar to the thermistor s expected resistance range Thermistors have much higher temperature coefficients than PRT so the tolerances on the reference resistor are correspondingly less demanding making them relatively inexpensive The top terminal should be connected to the screen of the thermistor s lead to minimise electrical noise picked up by the wires The high resistance of thermistors makes them more prone to picking up electrical noise it is therefore even more important to use a screened cable and connect this to the screen terminal on the microK than when using PRTs SYSE Page 56 of 117 Issue 1 05 5 Good Practi
16. as the calibration coefficients each time you use the thermometer and therefore avoids the associated risk of data entry errors The database also allows you to enter calibration due dates to ensure that you do not unwittingly use devices beyond their recalibration date The microK will warn you if you attempt to use a thermometer past its recalibration date you can disregard the warning and continue to use the thermometer but the warning will continue to re appear every hour until the out of calibration issue is resolved Enter data on the thermometers you use as reference standards or measurement devices into the microK s database see section 3 7 1 You can then use one of these thermometers by selecting it in the Thermometer box in the Settings tab see section 3 6 Svea Page 49 of 117 Issue 1 05 The database allows you to enter the following information about the thermometer Thermometer Name the name you use to refer to the thermometer Manufacturer Serial Number Calibration Due date Thermometer Type Minimum Temperature operating Maximum Temperature operating Conversion algorithm for converting base reading to temperature SO OE LO S amp S amp Information in the database is password protected to help you comply with the requirements of accreditation bodies 3 9 Using the Reference Resistors Database The microK contains a database that allows you to enter review and edit information a
17. copper Brass connectors must NOT be used V Voltage Source V Configure the microK to measure a Default Thermocouple with units set to Volts Use 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Single tab and clear the statistics After the microK has collected at least 100 readings shown as Mean of last in the Single tab record the Mean value and check that the standard deviation S D does not exceed 0 00000002V 0 02uV Calculate the require gain from gain geen Nae measured value Now apply the new gain by typing the command CAL GAIN POS gain SYSE Page 87 of 117 Issue 1 05 The value entered can be read back using CAL GAIN POS Repeat the procedure with the voltage source set to 50mV Apply the new negative polarity gain by typing in the command CAL GAIN NEG gain The value entered can be read back using CAL GAIN NEG SVS Page 88 of 117 Issue 1 05 9 RS232 Interface The microK is equipped with an RS232 interface This can be used to control the microK and perform calibration and diagnostic functions The command set uses the SCPI Standard Commands for Programmable Instruments protocol see section 11 for details 9 1 Establishing an RS232 Connection The RS232 connector is located on the rear of your microK see section 1 4 The connector is a 9 way male D type configured as a standard DTE device Name 1 CD 2
18. data sets and from this the software then calculates the uncertainty of the zero power extrapolated value Uncertainty on Zero Power Extrapolation 25 0019 25 0018 25 0017 25 0016 25 0015 25 0014 Resistance Ohms 25 0013 4 gt 25 0012 25 0011 I The effect of self heating is very small and can reasonable be regarded as linear with power If the actual zero power resistance is x and the measured resistance is Xn at current i then the measurements at the 2 currents will be ee ae od Pa x x ki where k is the unknown power coefficient Soreth Page 64 of 117 Issue 1 05 The extrapolated zero power value can easily be determined by eliminating k from these 2 equations x15 Xf Bi The mean of the results for the first and last third set of readings are used for x The mean of the middle second set of readings are be used for x2 The uncertainty in the zero power value is determined by 1 Calculating the uncertainties the standard deviation of the data set divided by the square root of the data set size u and uz for the two data sets used to calculate x and x2 2 Calculating the propagation of these uncertainties to the extrapolated value x by differentiating the above equation for x with respect to x or X2 3 Combining the effect of these two uncertainties u and uz using the root sum of squares The uncertainty in the extra
19. environment for at least 4 hours before checking or adjusting its calibration 8 1 1 Checking the Master Current Source The microK current source has 3 ranges 0 0 1mA 0 1mA and 0 10mA Check these by connecting a calibrated ammeter or DMM across the current terminals of channel 1 and connecting both the sense inputs to the red current terminal V Checking the master current source involves connecting a PC to your microK using a null modem RS232 cable and sending commands to it from Hyperterminal part of the standard Windows operating system installation or SYSE Page 78 of 117 Issue 1 05 another terminal emulator For further details of how to connect a PC to your microK see section 9 Once you have established communication with your microK type in the following commands and check that the measured current is within the given limits command current limits TEST CURR 0 1 0 0996 to 0 1004 mA TEST CURR 1 0 996 to 1 004 mA TEST CURR 10 9 96 to 10 04 mA TEST CURR 0 1 0 0996 to 0 1004 mA TEST CURR 1 0 996 to 1 004 mA TEST CURR 10 9 96 to 10 04 mA 8 1 2 Resistance Measurements The current reversal used by the microK to eliminate the effect of thermal EMFs means that it has an inherently stable zero for resistance measurement The zero ohms test does not form part of the calibrations process but is used to confirm correct operation of the measurement system It only needs to be checked on one c
20. heating of the platinum element generally a few mK This offset is nominally constant under given conditions and is often ignored since it should affect the thermometer equally during calibration and in use However the offset can vary even when conditions are apparently identical due to differences in the thermal contact between the thermometer and its environment This means that the same thermometer may exhibit a slightly different resistance when used in two Sors Page 12 of 117 Issue 1 05 identical temperature sources or even in the same temperature source after being removed and replaced This effect is significant in the most accurate thermometry work This uncertainty can be eliminated by determining the resistance of the SPRT at zero current zero power Whilst the resistance cannot be measured with zero current it is possible to measure the resistance at 2 different currents and extrapolate back to determine the value at zero current Historically the most common way to do this was to make a measurement at the normal current and then to increase or decrease the current by a factor of V2 1 414 This changes the power by a factor of 2 and allows easy determination of the zero power resistance by subtracting the change in resistance from the first measurement In fact a better method is to make a measurement at 2 currents that are in the ratio 0 56 1 see section 6 1 and then extrapolate back to the zero power value
21. monitoring the temperature of standards and liquid baths in your laboratory With three measurement channels expandable to 92 channels and the ability to measure all the temperature sensors you are likely to use in your laboratory the microK should be the only thermometry instrument you need in your calibration laboratory or measurement system They are also the first instruments of their type to be completely solid state making them highly reliable Despite their sophistication these instruments are very easy to use There are no knobs and dials just a colour touch screen that makes use of the familiar Windows CE operating system If you use a Windows operating system on your PC you will find these instruments intuitive and easy to use The USB port on the front panel allows you to plug in and use other devices that work with Windows CE such as a mouse keyboard or flash drive Readings can be displayed in resistance ratio ohms volts or temperature units C F or K Algorithms for conversion to temperature include PRTs ITS 90 Callendar Van Dusen IEC751 ASTM E1137 or custom coefficients Thermocouples TEC584 1 ASTM E230 amp E1751 for type B E J K N R S T Type L polynomial Gold Platinum Reference Function Polynomial Thermistor Steinhart Hart Sors Page 6 of 117 Issue 1 05 This manual provides a comprehensive guide to using the instrument We recognise that you will probably not wish to
22. off resistance of the semiconductors used to switch the signals Instead of a single switching device this technique uses two in series that operate together When the switches are off the mid point is connected by a third switching device to a buffered version of the output signal This means that there is virtually no voltage across the switching device Q2 when it is off and therefore no significant effect from the off resistance of that device Buffered Switching Arrangement This technique means that the microK contains no relays or switches apart from the on off switch and therefore offers unrivalled reliability without compromising measurement performance 7 4 Substitution Topology In conventional potentiometric instruments a common DC current is passed through a thermometer Rx and reference resistor Rs A voltmeter is switched between reading the voltage across Rx and Rs and the ratio of the two readings is calculated eS Page 73 of 117 Issue 1 05 Amplifier Conventional Potentiometric Resistance Measurement A significant source of error with this measurement topology is the common mode rejection ratio of the input amplifier The common mode signal at the input to the amplifier changes between the two measurements and will lead to an error at the input to the ADC In order to eliminate this source of error the microK uses a substitution topology in which there is a single point of measure
23. the total noise RMS summation of contributions is un 0 14nVHz The total noise is therefore reduced by a factor of 14 by the use of the impedance matching transformer This noise reduction technique can only be used with an AC resistance bridge it cannot be used in switched DC bridges or DC current comparator bridges and it is for this reason that AC resistance bridges have historically been the instrument of choice for primary standards temperature metrology as well as the most demanding temperature measurement applications In developing the microK we have devised a similar noise reduction technique for use in switched DC systems The technique involves using a number of amplifiers connected in parallel n IDENTICAL CIRCUITS Noise Reduction by Parallel Analogue Processing Sors Page 71 of 117 Issue 1 05 The output vo is the mean of the output signals vx from each amplifier x nV Da x n However since the input voltage noise is uncorrelated the noise signals sum statistically RMS summation If the voltage noise vn is the same but uncorrelated for each amplifier then the total voltage noise referred to the input is 2 x n vV v U X a e 2 o The current noise is simply the RMS summation of the current noise in for each amplifier giving a noise contribution in volts referred to the amplifier input of Un gt Vik SR In a similar way to the noise impedance matchi
24. this complexity is the contacts in switches relays connectors and potentiometers For this reason the microK was designed to have no switches apart from the on off switch mechanical relays or potentiometers The switches normally used for the operator interface have been replaced with a combination of an industrial grade touch screen over a full colour VGA LCD making the instrument both reliable and easy to use The internal connectors are limited to five ribbon cables with gold plated contacts for signal interconnections plus a small number of connectors for the AC power and internal DC supply Conventional instruments of this type use mechanical relays for some or all of the signal routing The microK uses only solid state switching The thermal EMFs from the metal silicon junctions in solid state switching devices are potentially higher than for mechanical relays under the same temperature gradient However the very small size of the die within the semiconductor devices means that there would be little opportunity for thermal gradients giving them a strong advantage over their mechanical counterparts In practice the thermal EMFs from solid state switching are significantly less than even the best mechanical relays As a result the microK achieves voltage offsets significantly less that 250nV 7 7 Inherent Stability The current reversals used to eliminate thermal EMFs from resistance measurements together with true 4 wire resista
25. to an external USB flash drive using the Backup Data button in the Instrument tab see section 3 7 9 The internal memory has a capacity of at least 1 8 GBytes which will accommodate more than 70 million PRT readings or more than 4 5 years of continuous logging at the fastest rate Select the destination for the data to open an Alpha Numeric Keyboard window and enter a filename An automatically incrementing default name based on the last filename used will appear in the entry box press OK to accept this or use the backspace and alpha numeric keys to enter your preferred filename If you try to use a filename that has already been used you will have to enter the password to proceed see section 3 11 for details on password protection The Shift key toggles the alpha keys between upper and lower case The indicator by the Start Save button shows whether readings are being recorded to a file The measurements are written to the file in comma delimited ASCII text form allowing easy importation into Microsoft Excel or other applications 3 5 The Multi Tab Select this tab to see all three channels in numeric form only The numeric display shows the last reading together with the mean and standard deviation for the most recent readings the number or readings in the statistics is set in the Settings tab for each of the channels that are enabled If the zero power extrapolation feature is being used the mean and standard deviations are replac
26. to protective earth Do not apply earth test currents to any front panel terminal nor to the shrouds of the USB RS232 GPIB or Ethernet connectors The product is designed to comply with EN 61010 1 and can be flash tested It is fitted with radio frequency interference suppressors Therefore it is recommended that only a D C test be performed Performing flash tests repeatedly can damage insulation This equipment contains no user serviceable parts Refer all repairs to qualified service personnel Contact Isothermal Technology or one of our appointed distributors for details of approved service outlets 1 3 Powering Up Your microK The microK operates on any standard AC electrical supply 88 264V RMS at 47 63Hz so unless your supply is unusual you can simply use the power cord provided to connect your microK to a suitable electrical outlet The power switch is located at the rear of the instrument immediately below the IEC connector When you turn your microK on it will go through a standard Windows CE boot sequence and then display a Window containing the Resume button Press Resume to restart the microK in the configuration it was in prior to the last power down you will then see the Main Window and be ready to operate your instrument Before pressing the Resume button make sure that any thermometers attached will not be damaged by the sense currents that will be applied the last values used If there is a problem disconn
27. to select the required sense current The standard PRT sense currents are available directly through the buttons provided Press the Custom button to specify a different value range 0 to 10mA this will then open a Numeric Keypad window Buttons for V2 and xvV2 are included to make manual extrapolation to zero power easier Uniquely the microK can be configured to automatically change the current between two values and extrapolate to determine a zero power resistance Press Zero Power Extrapolation to define the measurement sequence eS Page 37 of 117 Issue 1 05 Settling Time s 120 ai Normal Current mA 1 0000 Alternate Current mA 0 5600 Readings at Each Current 100 e OK Cancel Sequence 120s J100 Readings 120 s J100 Readings Use the ellipses button to specify the two currents used the number of readings taken at each current and the settling time allowed after the current is changed The Sequence details at the bottom of the window show the resulting measurement sequence The resistance is measured at normal current the alternate current and then returns to the normal current with settling delays after each current change Section 6 gives further details of the zero power extrapolation feature Press Clear Zero Power Extrapolation in the current window to cancel the zero power measurement sequen
28. units set to Volts Use 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Single tab and clear the statistics After the microK has collected at least 100 readings shown as Mean of last in the Single tab check Sors Page 82 of 117 Issue 1 05 that the Mean value agrees with the applied voltage to within 0 00000025V 0 25uV and that the standard deviation S D does not exceed 0 00000002V 0 02u V Repeat the procedure with the voltage source set to 50mV 8 2 Adjusting Calibration This section describes the procedures for adjusting the internal reference standards and the input offset voltages These can be performed by the user or a third party calibration provider subject to the availability of the standards specified below Isothermal Technology additionally checks the temperature coefficient of the zener reference and the linearity of the microK against an RBC resistance bridge calibration with an uncertainty of 0 01ppm We therefore recommend that you return your microK to Isothermal Technology or one of its appointed service centres annually for a comprehensive instrument calibration There are no potentiometers inside the microK to adjust calibration is implemented in software so can be performed without removing the cover from your microK Calibration is adjusted via the RS232 interface on the rear of the microK Connect the microK to a PC using a 9 pin null modem RS232
29. which will accommodate more than 70 million PRT readings or more than 4 5 years of continuous logging at the fastest rate Select the destination for the data to open an Alpha Numeric Keyboard window and enter a filename An automatically incrementing default name based on the last filename used will appear in the entry box press OK to accept this or use the backspace and alpha numeric keys to enter your preferred filename If you try to use a filename that has already been used you will have to enter the password to proceed see section 3 11 for details on password protection The Shift key toggles the alpha keys between upper and lower case The indicator by ee Issue 1 05 Page 34 of 117 the Start Save button shows whether readings are being recorded to a file The measurements are written to the file in comma delimited ASCII text form allowing easy importation into Microsoft Excel or other applications 3 6 The Settings Tab Select this tab to configure each channel for the required measurements Single Multi Settings Instrument Channel gt Thermometer oE ope e Units Current mA Default PRT 2 1 0000 A O onversion Samples per Read None fe za fay nge Ohms 125 2 ference Channel D Internal 100R CEEE Readings in Rolling Statistics q
30. will continue to re appear every hour until the out of calibration issue is resolved 3 7 4 Restart Software Press the Restart Software button to restart the microK software This is useful if you have added or removed microsKanners and want to re invoke the automatic discovery process without cycling the power 3 7 5 Update Software The software in the microK provides the user interface and controls the instrument It can easily be updated in situ Press the Update Software button to update the software in your microK The new application microk exe should be located in the root directory of a USB flash drive connected to the front panel USB connector You will be warned that this operation will restart the software press Yes to continue If the software finds a more recent software version on the flash drive you will be advised of the version levels and offered the opportunity to update to the later version You will be prompted to enter the password before proceeding If the flash drive does not contain a more recent version the software will simply restart The software automatically checks any USB flash drive connected to the front panel at start up If a more recent software version is found you will be offered the opportunity to upgrade 3 7 5 1 Update Firmware As well as the 32 bit processor on which the microK software runs to provide the operator interface the microK also contains an 8 bit processor that provid
31. Cancel Use the up down or ellipses buttons to change the GPIB address valid range 1 to 30 inclusive Use the up down buttons to select either Static IP Address or eS Page 46 of 117 Issue 1 05 Automatic DHCP addressing for the Ethernet port Use the ellipses buttons by each IP address byte to set a static IP address 3 7 8 Set Date and Time Press Set Date and Time to change the date and or time This opens a window to allow you to enter the current date and time and to select the date format dd mm yyyy or mm dd yyyy Year 2009 i Date Format dd mm yyyy Month 6 in O mm ddfyyyy Day 5 a Hour 13 E Minute 40 e Second 30 OK Cancel Press the ellipses buttons by each box to open a Numeric keypad window and enter the required value Press OK to save the changes and close the window Press Cancel to close the window without making any changes 3 7 9 Backup Data Press Backup Data to transfer data that has been saved to the internal memory see section 3 4 or 3 5 to an external USB Flash Drive You need to plug a USB Flash Drive into the front of the microK in order to use this facility otherwise a No external drive present warning will appear The operating system may take up to 20s to find the USB drive so you may have to for a while after plugging in the drive before being able to backup data eS
32. EMP sccsscssssscssssssssscsssssssssssssssssscsscssssessssnsssessssssessessssseess 75 7 6 Solid State Switching ccccssssscscsscsssssssssssssscsssssssssessssssnsscessssssessssssssesssssssssessesseess 76 7 7 Inherent Stability cccsscssccssssscsscsscsssssssssssssesssssesssscsssssssescsssssssesssssessesssssssssessossoess 76 7 8 Eliminating Self Heating Effects scsccsssssssscssssssscscssssssssscsscsssscssssnessesssssesssessessees 77 Be CALIBRATION ascospore eee ee eee 78 8 1 Checking Cali bratiomisc cscccccccscccscssvcvescesveceestsctestesvccateszsceccvetscsesevencvedsvcecsscsduecenscscdesessvereses 78 8 1 1 Checking the Master Current Source ceeesecesssneeeeeesneeeesenseeees 78 8 1 2 Resistance Measurements ceccceseseccecesneceeeseseeecesseeecesenaeeees 79 Sors Page 3 of 117 Issue 1 05 8 1 2 1 Zero Ohms Check e242 sees sceededs eos e a a aa i raaa 79 8 1 2 2 400 Q Internal Reference ReSistor cc cc ccececeeeceeeeeeeeees 80 8 1 2 3 100 Q Internal Reference ReSistor ccc ccceceeceeeeeeeeeees 81 8 1 2 4 25 Q Internal Reference Resistor cc cc ceeeseeeeceteeeeeeeees 81 8 1 3 Voltage Measurements ce eeeceesesseeceeseeeeeeeseeeceseteeeesseaeeesenaes 81 8 1 3 1 Zero Voltage Offsets innein n a oee ieii aia 81 8 1 3 2 Voltage Span Check oe eeesseceesseeeeeessneecessseeesesaeeeeenaes 82 8 2 Adjusting Calibration ccccssc
33. ISOs en micro User Manual Issue 1 05 Applies to microK 100 and microK 200 Software version 1 4 7 Firmware version 1 16 Isothermal Technology Limited Pine Grove Southport Merseyside NPL Pap one T 44 0 1704 543830 F 44 0 1701 544799 Technology Applied E info isotech co uk W www isotech co uk National Physical Laboratory CONTENTS 1 INTRODUCTION soe eee eee eae 6 1 1 Unpacking scsscscccccsscstsnsscssessensontsonsescenssasteseoscessedssosenetasenesesountenvasesenensescsssestssnceassadsasocscessesss 7 1 2 SALECY siocsseccsstensccssisncotsnconssassencontoeasesssssensoenetsessdheossosebensetesonoonsensesesedeoesenersesessegcomenateascessegseets 7 1 3 Powering Up Your Micro scssssscssssssssscssscccssssccssscssescssssssssessessssssssssssessssssessessosseees 9 1 4 A Quick Tour of YOur Micro K 23 i5cccccccesesecsccensesedeossensssosecenvsonssesscbecscssescestessscsesoesspsesesepesens 9 2 MAKING A MEASUREMENT TUTORIALS eeeeeeeeeeeseeee 12 2 1 Fixed Point Calibration of an SPRT Using Zero Power Extrapolation sss00 12 2 2 Measuring Temperature with an SPRT sccsccscssssssssscsscssesessssscsssssessssssessessecssessees 19 2 3 Measuring the Output from a Thermocouple ssccscsscsssssssssssscssssssssescsesscssesnese 25 3 DRIVING YOUR MICROK ccccscseseeeeeeeeeeneneeeeeeeeeseeneneeeeeeeeeeeeeaes 28 3 1 Int roduction cscsssssssc
34. R25 Where R235 is the value calculated for the 25Q internal reference 8 2 2 Calibrating Voltage Zeros Short out the 4 measurement terminals on all 3 channels using a piece of un insulated copper wire for each channel Type in the following commands to remove the zero offset correction for all three channels CAL OFFS1 0 CAL OFFS2 0 CAL OFFS3 0 Configure the microK to measure a Default Thermocouple with units set to Volts on all 3 channels Use 1 sample per reading and 100 readings in the rolling Statistics see section 3 6 Select the Multi tab and clear the statistics for all 3 channels After the microK has collected at least 100 readings shown as Mean of last in the Multi tab record the Mean for each channel and check that the standard deviation S D does not exceed 0 00000002 0 02u V SVS Page 86 of 117 Issue 1 05 Now adjust the zero offsets using the commands CAL OFFS1 offset CAL OFFS2 offset2 CAL OFFS3 offset3 Where offsetX is the zero offset measured for channel X The value entered for each channel can be read back using CAL OFFSX for channel X Re check the zero offsets for all three channels see section 8 1 3 1 8 2 3 Calibrating Voltage Span Connect a stable low noise voltage source with a nominal value of 50mV to channel 1 of the microK using low thermal EMF wire and connectors copper or an alloy such as tellurium copper that has a high copper content and low thermal EMF to pure
35. Resolution Resistance 0 001ppm of range Voltage nV Stability Resistance excluding resistance standard 0 note1 Voltage 3ppm year Measurement 2s Time Temperature J PRTs ITS 90 Callendar van Dusen Conversions Thermocouples IEC584 1 1995 B E J K N R S T L and gold platinum Thermistors Steinhart Hart Sensor Current 0 10mA in 3 ranges 0 1mA 0 4 of value 70nA resolution 28nA 1mA 0 4 of value 0 7uA resolution 280nA Svea Page 114 of 117 Issue 1 05 Keep Warm Current Cable Length Internal Standard Resistors Input Connectors Interfaces Display Operating Conditions Power Size Weight Notes 10mA 0 4 of value 7uA resolution 2 8uA 0 10mA 0 4 of value 7uA resolution 2 8uA lt 30m maximum 10Q per core or 10nF shunt capacitance 25 100 and 400 Q tolerance 0 1 TCR 0 05ppm C stability 2ppm over 10 years Cable Pod connectors for 4mm plugs spades or bare wires Contact material gold plated tellurium copper RS232 9 600 baud Ethernet IEEE 802 3 803 3u 100Base TX 10Base T USB 1 1 host 163mm 6 4 VGA 640 x 480 colour TFT LCD 15 30 C 50 85 F for full specification 5 40 C 40 105 F operational 10 80 RH 88 264V RMS 47 63Hz Universal 25W maximum 1 5A RMS maximum 520mm x 166mm x 300mm 20 5 x 6 6 x 11 9 W x Dx H 12 4kg 27lb 1 The microK uses a substitution tec
36. ails The GPIB connector is located on the rear of your microK see section 1 4 The connector is the standard IEEE 488 connector 24 way Name Function Pin Name Function DIO1 Data Input Output bit 13 DIOS Data Input Output bit DIO2 Data Input Output bit 14 DIO6 Data Input Output bit DIO3 Data Input Output bit 15 DIO7 Data Input Output bit DIO4 Data Input Output bit 16 DIO8 Data Input Output bit EOI End or Identify 17 REN Remote Enable DAV Data Valid 18 GND Ground paired with DAV NRFD Not Ready for Data 19 GND Ground paired with NRFD NDAC Not Data Accepted 20 GND Ground paired with NDAC IFC Interface Clear 21 GND Ground paired with IFC SRQ Service Request 22 GND Ground paired with SRQ ATN Attention 23 GND Ground paired with ATN GND Shield 24 GND Logic Ground Frame Ground cable screen Unlike the RS232 interface which is full duplex the GPIB is inherently half duplex data can only be transferred between the microK and the GPIB Controller in one direction at any given time this direction being determined by the controller If a response is expected from the microK the GPIB Controller must address the microK as a Talker in order that it can transmit this information The microK will try to send information on the GPIB for 2s after which time it will abandon attempts to respond and revert to being a Listener in order to received further commands on the GPIB This 2s window will start as soon as the micr
37. al memory you can backup the data to an external USB flash drive later see section 3 7 9 for details The raw data is saved in a comma delimited ASCII file together with microK settings information with the extension dat The processed zero power Soreth Page 18 of 117 Issue 1 05 measurements together with microK settings information is saved in a comma delimited ASCII file with the extension zpc These files can be transferred to a PC and analysed using Excel see section 3 7 9 for details Tip You can connect a calibrated SPRT to channel 3 in order to monitor the temperature of the external reference resistor simultaneously for lowest uncertainty use the external reference resistor on channel 2 rather than the microK s internal resistance standards as the reference resistance for this SPRT 2 2 Measuring Temperature with an SPRT The microK can be used with a calibrated SPRT to measure temperature with extremely low uncertainty For lowest uncertainty use an external DC or AC DC resistance reference standard maintained at a constant temperature in an oil bath or similar resistor maintenance system as the reference resistor rather than the internal resistance standards From start up press Resume to restart your microK Isothermal Technology microK 100 v1 4 4 S N 09 P119 firmware version 1 14 microsKanners detected none Resume Measurement system initialised
38. already been unlocked using the CALibrate UNLock command see section 11 6 38 Example to change the password from 1234 to ABCD use CAL PASS 1234 ABCD ABCD 11 6 38 Command CALibrate UNLock Format CALibrate UNLock lt password gt Unlocks the microK to allow calibration adjustment The microK always powers up in the locked state Calibration can be re locked by re powering the microK or using CAL LOCK see section 11 6 39 Example to unlock enable the calibration adjustment on a microK with the default password 1234 use CAL UNL 1234 11 6 39 Command CALibrate LOCK Format CALibrate LOCK Locks the microK to prevent calibration adjustment Example to lock the calibration of a microK after adjustment use CAL LOCK Sors Page 112 of 117 Issue 1 05 Sors Page 113 of 117 Issue 1 05 12 Specification Ranges Resistance Thermometers 0O to 100k Q Thermocouples 125mV Accuracy J UK 100 0 1ppm maximum over whole range for SPRT with Ro 2 2 50 equivalent to 0 025mK at 0 C or tr 0 1mK over full range 0 25ppm maximum over whole range for SPRT with Ro 0 250 uK200 0 2ppm maximum over whole range for SPRT with Ro 2 2 5Q equivalent to 0 05mK at 0 C or 0 2mK over full range 0 5ppm maximum over whole range for SPRT with Ro 0 250 Accuracy Voltage uncertainty 250nV between 0 and 20mV Thermocouples equivalent to 0 01 C for Gold Platinum thermocouple at 1000 C
39. appears If you are unfamiliar with touch screen devices such as PDAs you may initially feel that the touch screen interface is slow compared with using a mouse and keyboard but with a little practice you should quickly become comfortable with the technology and appreciate its benefits However if you prefer to use a USB mouse or keyboard you can simply plug these into the USB connector on the front panel They will immediately become active provided they use the standard class drivers built into the Windows CE operating system used in the microK To use more than one USB device simply plug a USB hub into the front panel connector Calibration data entered into the microK s database is password protected and includes recalibration dates the microK will alert you if you try to use a thermometer or reference resistor after its recalibration date This feature ensures the integrity of your measurements and helps you to comply with the requirements of accreditation bodies 3 2 The Start Up Window When power is applied to the microK it goes through a Windows CE boot sequence that loads the operating system and then starts the microK application The start up window then appears showing the microK s model and serial number together with the version numbers for the measurement system firmware and microK software used The window also lists the details of any microsKanner multiplexers connected to the microK the microsKanner
40. ard window and enter a name for the configuration Configurations stored to a USB flash drive are located in directory microKData serialnumber backups Sore Page 48 of 117 Issue 1 05 where serialnumber is the serial number if the microK This means that you can have duplicate configuration names filenames for configurations provided they apply to different instruments If you want to transfer a configuration from one microK to another you will need to move the configuration file manually on the USB flash drive between the sub directories for the two microKs 3 7 12 Load Configuration Press Load Configuration to load a configuration settings for the microK You will be prompted to enter the password before proceeding You will then be offered the choice buttons of loading the configuration from the Internal memory solid state drive or an External USB flash drive Press the required button and then use the up down buttons to select the required configuration Press OK to load the configuration or press Cancel to close the Window without loading the configuration 3 8 Using the Thermometer Database The microK contains a database that allows you to enter review and edit information about the thermometers you use You can then select a thermometer from this database and all the parameters associated with it will be loaded and used by the measurement system This means that you do not need to enter information such
41. as to measure the signal across both to determine the resistance of the device under test Example to set the microK to measure a PRT that has a maximum resistance of 130Q using a 100Q reference resistor with a 1mA sense current use SENS FRES RANG 130 1 This will set the microK to the 0 5V range 11 6 14 Command SENSe FRESistance RANGe Format SENSe FRESistance RANGe UPPer Reports the range for the next resistance measurement at the present sense current set using the CURRent command The current used to calculate the range may be different from that specified when the range was set using the SENSe FRESistance RANGe command The reported range is the actual range for the measurement system at the present sense current Sore Page 104 of 117 Issue 1 05 Example a microK that has had its resistance range set using the command shown in section 11 6 13 but has its sense current set to 10mA would respond to the command SENS FRES RANG with 50 000000 11 6 15 Command SENSe RATio REFerence Format SENSe RATio REFerence lt reference channel gt Selects the reference channel for the next resistance ratio measurement made The channel is not actually selected until a measurement is started using either the INITiate or READ commands The channel numbers used for the internal reference resistors are Channel 203 25 Q l Channel 204 100 Q l Channel 205 400Q Example to select channel 2 as the refere
42. bout the reference resistors you use You can then select a reference resistor from this database and all the parameters associated with it will be loaded and used by the measurement system This means that you do not need to enter its value each time you use it and therefore avoids the associated risk of data entry errors The database also allows you to enter calibration due dates to ensure that you do not unwittingly use devices beyond their recalibration date The microK will warn you if you attempt to use a reference resistor past its recalibration date you can disregard the warning and continue to use it but the warning will continue to re appear every hour until the out of calibration issue is resolved Enter data on the reference resistors you use with your resistance thermometers into the microK s database see section 3 7 2 You can then use one of these reference resistors using the Reference Resistor box in the Settings tab see section 3 6 The database allows you to enter the following information about the reference resistor Resistor Name the name you use to refer to the resistor Manufacturer SYSE Page 50 of 117 Issue 1 05 Serial Number Calibration Due date Value calibrated value in ohms Information in the database is password protected to help you comply with the requirements of accreditation bodies 3 10Saving Instrument Configurations You can save the current configuration set
43. box PRTs and thermistors only Use the up down buttons to select the required range The microK provides two ranges for resistance thermometers The resistance ranges offered depends on the sense current use the ellipses button by the Current box in this tab to change the current Choose a resistance range that is greater than or equal to both the thermometer resistance and reference resistor value you intend to use Reference Channel box PRTs and thermistors only Use the up down buttons to select the reference resistor used in the resistance measurement either one of the internal reference resistors or the channel to which an external resistance standard is connected Alternatively press the ellipses button to open the Reference Channel window and select the channel directly The External button in this window allows you to select one of the microK s three external channels or any expansion channel provided by a microsKanner Reference Resistor box PRTs and thermistors only If an internal reference resistor was selected in the Reference Channel box this box will show the calibrated value of that resistor If one of the input channels was selected in the Reference Channel box this box will contain a list of the reference resistors in the microK s database entered using the Edit Resistors button in the Instrument tab see section 3 7 2 and Uncalibrated Select the required resistor using the up down buttons Select Unca
44. button is replaced by the Details button SYSE Page 17 of 117 Issue 1 05 single Multi Settings Instrument Channel ae a Clear Graph Ohms 24 999491 Zero Power Value Start Save Set Scales 0 000002 Uncertainty 24 9998000 24 9997500 24 9997000 24 9996500 24 9996000 24 9995500 3 400 3 500 3 600 3 700 3 800 3 900 4 000 Time js After enabling zero power extrapolation it can take many minutes before the first measurement data sets have been collected and the zero power value calculated Press Details to open a window and see the status of the measurement sequence Measurement 1 3 a Close Status Reading 89 100 Current 1 0 56 1 mA Mean 24 999805 24 999590 24 999805 Ohms StdDev 0 000009 0 000013 0 000009 Ohms 24 99981 24 99960 24 99982 24 99979 24 99959 24 99980 24 99982 24 99959 24 99981 24 99979 24 99959 24 99979 24 99981 24 99961 24 99979 24 99981 24 99960 24 99982 24 99980 24 99958 24 99980 24 99980 24 99956 24 99981 24 99980 24 99959 24 99980 24 99980 24 99959 24 99981 24 99981 24 99960 24 99981 24 99980 24 99958 24 99980 24 99981 Press Close to return to the main window To save the data press Start Save you will then be offer the choice of saving to the Internal memory or an External USB flash drive memory stick If you choose the intern
45. cable and establish an RS232 connection with it using Hyperterminal at 9 600 Baud for further details of how to connect a PC to your microK see section 9 1 Confirm that the RS232 link is working by typing in IDN terminate this and all commands shown in this section by pressing the carriage return or enter key The microK will respond with a string in the form Isothermal Technology microK 100 09 P119 firmware version 1 14 The calibration of your microK is password protected Unlocked the calibration to allow calibration adjustment using the command CAL UNL password where password is the calibration system password NOT necessarily the same as the password used in the touch screen operator interface The password is initially set to 1234 but should be changed for security reasons see section 11 6 35 You can now use the SCPI commands see section 11 6 detailed below to adjust the microK s calibration SYSE Page 83 of 117 Issue 1 05 8 2 1 Calibrate Master Current Source The microK s current source has 3 ranges 0 0 1mA 0 1mA and 0 10mA These share a common reference and the tolerance between the ranges is sufficiently small that it is only necessary to calibrate the 1mA range in order to achieve the full performance specification The current is controlled by a DAC so adjustment is made in software by scaling the DAC value as required Connect a calibrated ammeter or DMM across the current terminals of cha
46. ccceeeeeeeeees 111 11 6 35 Command CALibrate GPIB ADDRESS ccccceeecccceeeeeeeeeen 111 11 6 36 Command CALibrate GPIB ADDReSs 0 0 0 eeee ccc eeeeeeeeee 111 11 6 37 Command CALibrate PASSWotd ccccccceeecccceeseeccceeeeeseeees 112 11 6 38 Command CALibrate UNLOck cccccec cc cceeeccccesesccceeeeeeeeees 112 11 6 39 Command CALibrate LOCK 1 0 0 cece ccceeecccceeeeeccceeeeeeseees 112 12 SPECIFICATION aaraa p a aene e Lanai a iiih 114 R APPROVALS a aaa aaraa aa aaa a aaia hanO aain iaia 116 13 1 CE Declaration siseses eccsccsss ce Swstcgescccc cack cb si dade ese d sdaeeateniaesees cadcedeveloasede cdsavedesoasddctece 116 13 2 BOC State me iit ssccccccccscsckiccceescdschccecessesecescieteccossdeticcsciescsseboaucecotcdsesacceccacsssscocasoctessie 116 13 3 Standards Applied ssccscssssssssssscsssesesessscssssssssssscsscssssessssessessssssessessessessseesess 117 SuSE Page 5 of 117 Issue 1 05 1 Introduction The microK 100 and microK 200 thermometry bridges use a completely new ADC analogue to digital converter and low noise amplifier technology see section 7 The microK Technology to provide levels of performance previously only available using AC resistance bridges Uniquely the microK bridges also work with thermocouples and thermistors so that they can be used to calibrate precision noble metal thermocouples type R S and the new gold platinum thermocouple as well as simply
47. ce Guidelines 5 1 Using Internal External Reference Resistors The microK s internal reference resistors are the best commercially available foil resistors having a temperature coefficient of only 0 0S5ppm and a stability of 2ppm over 10 years However their temperature is not controlled and they will therefore not be as accurate as an external resistance standard maintained at a known temperature The microK is capable of measuring resistance ratio to better than 0 1ppm so if you want to make use of this accuracy in performing a resistance measurement it is better to use a good external reference resistor such as a DC or AC DC resistance reference standard maintained at a constant temperature in an oil bath You will not be able to measure resistance to 0 1ppm using the internal resistors The internal resistors are useful for less accurate work PRT measurements to a few mK or in comparison calibrations where any error in the value of the reference resistors causes a corresponding error in the temperature measured by the reference thermometer which largely cancels out the effect of the error in the resistance measurement 5 2 Making a Good Electrical Measurement Although the microK is intended for use in temperature metrology its base measurements are electrical resistance or voltage The limited sensitivity of PRTs and thermocouples means that in order to achieve uncertainties at the mK level we need to make electrical meas
48. ce and return to a steady measurement current Samples per Reading box Use the up down buttons to select the number of samples you want to average together to form a single reading Alternatively press the ellipses button to open a Numeric Keypad window and enter the required number directly The number of samples may be between 1 and 100 inclusive Increasing the number of samples will slow down the rate at which readings are made but will also reduce the uncertainty associated with these readings as shown by the standard deviations reported in the Single and Multi tabs This uncertainty reduction is proportional to the square root of the number of samples for example selecting 16 samples per reading will reduce the uncertainty associated with each reading by a factor of 4 SVS Page 38 of 117 Issue 1 05 Readings in Rolling Statistics box Use the up down buttons to select the number of samples in the rolling statistics Alternatively press the ellipses button to open a Numeric Keypad window and enter the value directly Values between 1 and 1000 inclusive may be used 3 7 The Instrument Tab Select this tab to enter information into the microK s database for thermometers and reference resistors adjust instrument settings GPIB or IP address time date and password update the software or firmware and manage data Edit Thermometers Edit Resistors Calibration Restart Softwar
49. common practice to measure the ratio of the resistance of the two thermometers rather than measure their individual resistances in a comparison calibration This has the advantage of reducing the calibration uncertainty be elimintating one of the measurements involved eS Page 24 of 117 Issue 1 05 2 3 Measuring the Output from a Thermocouple The microK is capable of measuring temperature using a thermocouple But a more common use would be to calibrate a thermocouple against another more accurate thermocouple or an SPRT This tutorial describes how to measure the output voltage from a thermocouple in volts From start up press Resume to restart your microK Isothermal Technology microK 100 v1 4 4 S N 09 P119 firmware version 1 14 microsKanners detected none When the main window opens press the Settings tab Measurement system initialised Settings Instrument Jk Clear Graph C Mean o Start Save Set Scales SD Clear 10 ODrPNWRU THD YO 0 0 Time f s In the Settings tab disable channels 2 and 3 this will speed up measurements on channel 1 which we will be using by using the up down buttons by the Channel box to select these channels and pressing Disable Use the up down buttons to Soreth Page 25 of 117 Issue 1 05 return to channel 1 Use the up down buttons by each box to select the requ
50. csensececestssonsoesescesesstsconedescesssesccsssesoeesvossarees 96 11 4 Parameters iecccccssstesscscnsactecesececsic sesscstesecsddsssdescestevacastedecdsonassescdcnstscensucestessocededeseacedscesee 96 11 5 UMS AEETIS ERE EE A ETETE EEE ATE 96 11 6 Making Measurements using SCPI Commannd scscssssssssscssescesssssssesssssseeseees 98 11 6 1 Measuring Resistance using SCPI Commands eeeeeeee 98 11 6 2 Measuring Voltage using SCPI Commands sseeeeeeeeeeeeeeeeeee 99 11 6 3 Measuring Temperature using SCPI Commands 064 99 11 6 4 SCPE Commands 00 0 ccccccsceccceccececeeeceeeceeeeeeeeeeeeeeeeees 101 11265 Command TDN oieta eoe I ee 102 11 6 6 Command RST io ccecccccccceeeceeeeeeeeceeeeeeeeeeseeeeseeeeees 102 11 6 7 Command SENSe FUNCtion i cccccccccececeeeeeeeeeeeeeees 102 11 6 8 Command SENSe FUNCtion 0 0 ccccccccccceceeeeeeeeseeeeees 102 11 6 9 Command SENSe CHANnDiel cccccccccccccccccccceceeeeeeceeeeeeees 103 11 6 10 Command SENSe CHANnel cc cc ccccccccccccceceeeeeeeeeeeeeees 103 11 6 11 Command SENSe FRESistance REFerence cccceceees 103 11 6 12 Command SENSe FRESistance REFerence ccccccceees 103 11 6 13 Command SENSe FRESistance RANGE cccccccccceceeeeees 104 Svea Page 4 of 117 Issue 1 05 11 6 14 Command SENSe FRESistance RANGE cccce cc ceeccceeecee sees 104 11 6 15 Command SENSe RATI0 REFere
51. d reference resistor Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter a serial number The Shift key toggles the alpha keys between upper and lower case Calibration Due box This box contains the date when calibration is due for the selected reference resistor Press the ellipses button by the box to open a Date Entry window and enter a date The ellipses buttons by the Day Month and Year boxes in the Date Entry window open a Numeric Keypad window Dates are checked for validity including leap years for dates up to 31 December 2099 Value box This box contains the calibrated value for the selected reference resistor If you are creating a new reference resistor entry press the ellipses button to open a Numeric Keypad window and enter the calibrated resistance value in ohms New button Press this button to make a new reference resistor entry into the microK s database Delete button Press this button to delete the selected reference resistor or the current entry for a new reference resistor from the database OK button Press this button to confirm the changes and close the window Sore Page 43 of 117 Issue 1 05 3 7 3 Calibration Press Calibration to open a Date Entry window and set a recalibration date for your microK The microK will warn you if you attempt to use it past this recalibration date you can disregard the warning and continue to use it but the warning
52. devices used in the ADC and the preceding pre amplifier Another benefit of the new ADC is its speed The implementation used in the microK provides conversions to full accuracy in 100ms This together with the use of solid state switching allows for a very fast reversal rate which in turn helps to eliminate the effect of any thermal EMFs and reduce the noise since the system can operate above the corner frequency of the amplifiers 1 f noise 7 2 Parallel Low Noise Amplification With the ADC s low noise contribution the microK s overall noise performance is determined primarily by the input noise of the amplifier used to sense the small voltage developed across the PRT This noise is generated by the amplifier s input voltage noise and its input current noise flowing through the input impedance Typical figures for low noise operational amplifiers or discrete semiconductors are around 2nVHz and 0 2pAHz respectively The input noise U for an input impedance of Z 25Q can be calculated by performing an Sors Page 69 of 117 Issue 1 05 RMS Root Mean Square summation of the noise contributions from the voltage noise vn and current noise in U v i Zy U 2x10 0 2x10 x25 2 000006nVHz The voltage noise clearly dominates the result and the contribution of the current noise is truly negligible By using different semiconductor technologies and operating conditions bias current
53. e Update Software Change Password 3 7 1 Edit Thermometers System Calibration x Single Multi Settings Instrument Port Settings Set Date and Time Backup Data Clear Data Files Backup Configuration Load Configuration Press Edit Thermometers to create edit or delete a thermometer in the database You will be prompted to enter the password in order to proceed Sule Page 39 of 117 Issue 1 05 tt ISPRT 1 Thermometer Thermometer Name Thermometer Type SPRT 1 ia IPRT Manufacturer s Name Min Temperature C Isothermal Technology ar 259 35 Serial Number Max Temperature C 66032_123 961 78 Calibration Due Conversion 15 12 2008 E Delete Coefficients ol JE OE Thermometer box Use the up down buttons to select the thermometer you wish to edit or delete Alternatively press the New key to create a new thermometer entry The default thermometer types are included in the list but cannot be edited or deleted Thermometer Name box This box contains the name of the selected thermometer Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter edit a name The Shift key toggles the alpha keys between upper and lower case Manufacturer s Name box This box contains the manufacturer of the selected the
54. e to the PRT PRT The top terminal should be connected to the screen of the PRT s lead to minimise electrical noise picked up by the wires 4 5 Connecting Thermocouples external Ice Point or WTP The microK s measurement system uses active guarding As a result the voltage measurement system is floating until it is connected to the sense current terminals In order to measure the voltage on a thermocouple the two current Sorah Page 54 of 117 Issue 1 05 terminals should be connected to each other and to the red voltage sense terminal Thermocouple Measurement Junction Reference Junction The most accurate thermocouple measurements are made with the reference junction immersed in an ice point bath or water triple point The microK supports this arrangement by allowing you to specify the temperature of the reference junction as 0 C or 0 01 C see section 3 6 4 6 Connecting Thermocouples using RJ compensation It is possible to measure the temperature of a thermocouples reference junction and compensate for the associated EMF The reference junction can be measured using a PRT or thermistor connected to another measurement channel l O Thermocouple Vv Measurement Reference V o V Junction Junction R1 The microK supports thus arrangement by allowing you to use a temperature measured by another input channel as the reference junction temperature
55. e 107 of 117 Issue 1 05 lt reference gt SENS FRES RANG lt resistance range gt lt current gt SENS CHAN lt channel gt and READ Example to set the microK to measure a PRT on channel 1 that has a maximum resistance of 130Q using a 100Q reference resistor on channel 2 with a ImA sense current use MEAS FRES1 REF2 130 1 11 6 24 Command MEASure RAT REF Format MEASure SCALar RATio lt channel gt REFerence lt reference gt lt resistance range gt lt current gt Initiates and reports a resistance ratio measurement on lt channel gt against a reference on channel lt reference gt using lt resistance range gt with sense lt current gt note that there is no gap between the command and the channel numbers as this command makes use of the numeric suffices feature of SCPI described in section 11 3 This command is equivalent SENS FUNC rat SENS RAT REF lt reference gt SENS RAT RANG lt resistance range gt lt current gt SENS CHAN lt channel gt and READ Example to set the microK to measure the resistance ratio of a PRT on channel 1 that has a maximum resistance of 130Q against a 100Q reference resistor on channel 2 with a ImA sense current use MEAS RAT1 REF2 130 1 11 6 25 Command CURRent Format SOURce CURRent lt current gt Set the sense current for the next resistance or ratio measurement to lt current gt The current is not changed until a measurement is started using either the INITiat
56. e harmful interference in which case the user will be required to correct the interference at his own expense Changes or modifications to this equipment not expressly approved by Isothermal Technology could degrade EMC performance and void the user s authority to operate the equipment Sors Page 116 of 117 Issue 1 05 13 3 Standards Applied The following standards have been applied in assessing compatibility with the requirements for CE marking and for FCC compliance N61326 1997 amp CFR47 2005 N61326 1997 amp CFR47 2005 N61326 1997 Conducted Emissions E Radiated Emissions E Conducted Immunity E Radiated Immunity EN61326 1997 Electrical Fast Transients EN61326 1997 Electrostatic Discharge EN61326 1997 Surge EN61326 1997 Voltage Dips amp Interruptions EN61326 1997 Harmonic Currents EN61000 3 2 2000 Flicker EN61000 3 3 1995 Electrical Safety EN61010 1 2001 Sors Page 117 of 117 Issue 1 05
57. e or READ commands Example to set the sense current for the next resistance measurement to 2mA use CURR 2 11 6 26 Command TEST CURRent Format TEST CURRent lt current gt Sors Page 108 of 117 Issue 1 05 Immediately sets the sense current on channel to lt current gt Example to set the sense current on channel 1 to 5mA use TEST CURR 5 11 6 27 Command CALibrate CURRent Format CALibrate CURRent lt actual current gt This command is used after using the TEST CURR 1 command and measuring the current from channel 1 see section 8 2 1 It uses the actual current entered to adjust the master current source to the correct current The adjustment is only applied if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 Example the current from channel 1 after using the command TEST CURR 1 was measured as 1 00123 To adjust the master current source correctly use CAL CURR 1 00123 11 6 28 Command CALibrate REFerence Format CALibrate REFerence lt reference gt lt actual resistance gt Used to calibrate the internal lt reference gt standard by assigning a new lt actual resistance gt to it The adjustment is only applied if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 The channel numbers numeric suffices used for the internal resistor are given in section 11 3 The calibrated value is stored as a floating poi
58. each measurement sequence and see the results appear by pressing Details in the Single of Multi tabs single Multi Settings Instrument Channel 2 i o a Clear Graph Ohms 24 999491 Zero Power Value e Start Save Set Scales 0 000002 Uncertainty 24 9998000 24 9997500 24 9997000 24 9996500 24 9996000 24 9995500 3 400 3 500 3 600 3 700 Time s 3 800 3 900 4 000 The Details window shows the current status of the measurement and allows you to look back at earlier measurements by using the Up Down buttons by the Measurement field Sors Page 63 of 117 Issue 1 05 Measurement 1 3 a Close Status Reading 89 100 Current 1 0 56 1 mA Mean 24 999805 24 999590 24 999805 Ohms StdDev 0 000009 0 000013 0 000009 Ohms 24 99981 24 99960 24 99982 24 99979 24 99959 24 99980 24 99982 24 99959 24 99981 24 99979 24 99959 24 99979 24 99981 24 99961 24 99979 24 99981 24 99960 24 99982 24 99980 24 99958 24 99980 24 99980 24 99956 24 99981 24 99980 24 99959 24 99980 24 99980 24 99959 24 99981 24 99981 24 99960 24 99981 24 99980 24 99958 24 99980 6 1 Zero Power Uncertainty Calculation The software calculates the standard deviation for the three data sets in the measurements These are used to determine the uncertainty of the mean of these
59. ecoming electrically live and therefore a hazard to the operator Suitable precautions should be taken such as using an isolating transformer in the supply to such a furnace If you require further advice on safety issues please contact Isothermal Technology or one of Sors Page 7 of 117 Issue 1 05 our appointed distributors we have extensive experience of thermometry and can provide advice and equipment to help you Retain these instructions Use only as specified in these operating instructions or the intrinsic protection may be impaired Please observe the following safety precautions Do not use your microK if it is damaged Only connect to an earthed supply socket THIS UNIT IS CLASS 1 CONSTRUCTION AND MUST BE EARTHED Connect only to a power supply with a voltage corresponding to that on the rating plate This equipment is for indoor use and will meet its performance figures within an ambient temperature range of 5 C to 40 C with maximum relative humidity of 80 for temperatures up to 31 C decreasing linearly to 50 RH at 40 C Equipment is for operation at installation category II transient voltages and pollution degree 2 in accordance with IEC 664 at altitudes up to 2000 metres Before replacing a fuse DISCONNECT THE EQUIPMENT FROM THE ELECTRICAL SUPPLY The fuse is contained in the IEC socket on the rear panel It must only be replaced with a fuse of the type and rating marked on the rear pa
60. ect your sensors before proceeding and then reconnect them after changing the sense current to the required values 1 4 A Quick Tour of Your microK On the front panel of your microK you will find the input terminals for the three measurement channels the touch screen colour display and a USB connector SYSE Page 9 of 117 Issue 1 05 Input Touch Screen Terminals amp Display Connector Input Terminals The input terminals accept 4mm plugs spades or bare wires The current I and voltage sense V terminals are spaced on 34 centres so that standard BNC to 4mm adaptors not supplied can be used to connect to thermometer sensors that have BNC terminations The contact material for the connectors is gold plated tellurium copper offering extremely low thermal EMFs when connected to copper wires connectors This is essential when using precision thermocouples Display The display is a colour TFT VGA 640 x 480 LCD with a long life CCFL cold cathode fluorescent lamp backlight A touch panel is mounted in front of the display so that you can control the instrument by simply touching the buttons displayed on the LCD The touch panel is an industrial grade component offering good durability It is intended to be operated with a finger A stylus intended for PDAs may also be used never use a sharp object with the touch panel as this may lead to premature failure The USB Connector The USB connector is primar
61. ed by the Zero Power Value and Uncertainty values and the Clear button is replaced by the Derails button see section 6 SYSE Page 33 of 117 Issue 1 05 Single Multi Settings Instrument Ohms Start Save Channel 1 24 9997 24 999696 Mean of last 100 0 000010 SD Clear a2 0 0000000 vots 0 000000032 Mean of last 100 0 000000036 SD Clear Channel 3 The displayed values are updated as new readings are taken The time between readings depends on the settings for that channel and any other channels that are also enabled This can vary between 2 seconds and 5 minutes The shortest measurement time is 2s so if all three channels were enabled and working at this fastest rate each channel would be updated every 6s Clear buttons Press the Clear button to clear reset the statistics for each channel Start Save Press the Start Save button to record all the measurements being made You will then be offered the choice buttons of storing the data to the Internal memory solid state drive or an External USB flash drive Data stored to the internal memory is preserved when power is removed and can subsequently be transferred to an external USB flash drive using the Backup Data button in the Instrument tab see section 3 7 9 The internal memory has a capacity of at least 1 8 GBytes
62. een protector to your microK not supplied but available from local suppliers to protect the 6 4 screen The touch screen can be cleaned with a damp not wet cloth Use either a proprietary screen cleaner suitable for PC flat panel displays or water and a little mild liquid soap on a lint free cloth to wipe the touch screen Dry the screen immediately after cleaning with a lint free cloth The rest of the microK should not require cleaning as often as the display and can be cleaned in the same way as the screen Never use abrasive cleaners such as cream cleaners on your microK Sors Page 60 of 117 Issue 1 05 6 Making Zero Power Resistance Measurements The sense current used to measure the resistance of a PRT for example the 1mA used with a 25Q SPRT causes a small but significant amount of self heating of the platinum element generally a few mK This offset is nominally constant under given conditions and is often ignored since it should affect the thermometer equally during calibration and in use However the offset can vary even when conditions are apparently identical due to differences in the thermal contact between the thermometer and its environment This means that the same thermometer may exhibit a slightly different resistance when used in two identical temperature sources or even in the same temperature source after being removed and replaced This effect is significant in the most accurate thermometr
63. ees 54 4 5 Connecting Thermocouples external Ice Point Or WTP scsccccssssscsessessssssesseees 54 4 6 Connecting Thermocouples using RJ compensation ccsccsssssssscsscsssssssssssesseees 55 4 7 Connecting Thermistors cccsccssscsssssssssscccesesssssssssessssssnssssssesssssssssessesssessessssssees 56 5 GOOD PRACTICE GUIDELINEG ccccccssesseeeeeeeeseeeseeeeeeeeeseeeee 57 5 1 Using Internal External Reference Resistors scsccscsssesscsscssssssssscssscsssseessessesseees 57 5 2 Making a Good Electrical Measurement sccscssssscssssssssscsscsesscssssssssessssssssssssesseees 57 5 3 Looking After Your microK cscsscssssssesssssssscssssssscsesssssnsscssssssscssssssssesssssssssessssseess 59 6 MAKING ZERO POWER RESISTANCE MEASUREMENTS 61 6 1 Zero Power Uncertainty Calculation ccscssccsssscsssssssssssssessscsscssssssssesssssssssessessees 64 7 THE MICROK TECHNOLOGY sccccceeeseeseeceeeeeseeseeeeeeeeeeneeseaes 67 TA The ADC iesiri Ea E Ea EEE EE E E eS 67 7 2 Parallel Low Noise Amplification cccsccssscescssscssscssssssscssssssssscscsssssccssesessesssseees 69 7 3 Buffered Switching ccsccsccssssssscsscsssssssssssssessessssssssesssessnescescssssessesnsssesssssssssessosseess 72 7 4 Substitution Topology sccscsssscscsscssssssssssscssssssssssssesssssssssscesssessssssssesssssssssesssssess 73 7 5 Minimising Thermal
64. ellurium copper contacts These generate exceptionally low thermal EMFs when connected to the copper terminations used on standards grade thermocouples The connectors accept 4mm plugs bare wires or spade terminations Additionally they are spaced on 19mm 34 pitch so that they can be used with standard 4mm to BNC adaptors not supplied for connecting to BNC terminated SPRTs The mechanism is designed so that the clamping surface does not rotate as it clamps the wire in order to avoid damaging it The Cable Pod mechanism is made from a high strength polymer but nonetheless may be subject to mechanical damage if the connectors are over tightened Please tighten the terminals to a light finger tight level in order to ensure that they are not subject to undue wear or premature failure This is all that is required electrically do not try to use the connector to provide strain relief or tension a cable 4 2 Connecting PRTs 4 wire The microK s resistance measurement system is optimised for high accuracy 4 wire resistance measurement The PRT should be connected to the chosen input channel in accordance with the schematic shown on the microK s front panel as follows SPRT SYSE Page 52 of 117 Issue 1 05 The top terminal should be connected to the screen of the SPRT s lead to minimise electrical noise picked up by the wires 4 3 Connecting PRTs 3 wire The microK can be connected to
65. ence Channel Reference Resistor 2 Em J a le 2 1 0000 e Samples per Reading of Readings in Rolling Statistics DaDa WILKINS 1 vj Press the Single tab to see the measurements in numeric and graphical form Set the graph scales by pressing Set Scales This opens the graph scales window Ensure that autoscaling is turned on press Autoscale to toggle autoscaling on off the status of autoscaling is shown by the adjacent indicator Use the radio and up down or ellipses buttons to set the x axis to 60 minutes Y Axis Channel li i Minimum 0 Maximum f Autoscale X Axis Scale Minutes 60 oim Time Units Seconds Minutes OK Cancel Press OK to return to the main window The measurement system will now accumulate data and after 60 minutes the graph will begin to scroll to show the last 60 minutes of data SuleGh Page 23 of 117 Issue 1 05 To save the data press Start Save you will then be offered the choice of saving to the Internal memory or an External USB flash drive memory stick If you choose the internal memory you can backup the data to an external USB flash drive later see section 3 7 9 for details The data is saved in a comma delimited ASCII file together with microK settings information
66. es low level control of the measurement hardware We used the term firmware for the SYSE Page 44 of 117 Issue 1 05 program in the 8 bit processor to distinguish it from the software that provides the operator interface This firmware can also be updated easily in situ As with updating the software press the Update Software button to update the firmware in your microK The new firmware microK100 version x_xx hex should be located in the root directory of a USB flash drive connected to the front panel USB connector You will be warned that this operation will restart the software press Yes to continue If the software finds a more recent firmware version on the flash drive you will be advised of the version levels and offered the opportunity to update to the later version You will be prompted to enter the password before proceeding If the flash drive does not contain a more recent version the software will simply restart In order to update the firmware you will be asked to turn the power off and then on again This will start the firmware update which takes approximately 3 minutes during which time a progress bar is displayed If power is lost during the update the process will restart automatically when power is restored Once the update is complete the microK displays the normal start up window The software automatically checks any USB flash drive connected to the front panel at start up If a more recent firmwa
67. esistance at two sense currents and then extrapolating back to the zero power value The microK s user interface provides a simple feature to allow the sense current to be scaled by a factor of V2 a factor of 2 in power to make this technique easy for the user to implement see section 3 6 The microK can be configured to change the current between two values and extrapolate back to determine a zero power value automatically see section 6 Sors Page 77 of 117 Issue 1 05 8 Calibration The ADC and measurement topology used in the microK are inherently very stable with both time and temperature The stability of the microK is primarily determined by its internal standards a zener reference for voltage and bulk metal foil resistors for resistance We have used the best available components for these internal standards a Linear Technology precision zener reference of the type used for voltage transfer standards in electrical metrology and Vishay hermetically sealed bulk metal foil resistors To keep your microK operating within its performance specification it should be recalibrated annually Please contact Isothermal technology to arrange this calibration 8 1 Checking Calibration The calibration can be checked by measuring known standards with the microK The calibration should be performed in a temperature controlled environment between 19 C and 25 C The microK should be powered up and left to stabilise in the calibration
68. ess OK to return to the main window The measurement system will now accumulate data and after 10 minutes the graph will begin to scroll to show the last 10 minutes of data Tip The microK provides reference functions for standard thermocouples to convert the measured voltage to temperature You can also enter a third order polynomial as the individual deviation function for a calibrated thermocouple B Single Multi Settings Instrument Channel o a Clear Graph 0 0000020 vors 0 000001989 2 4000000e 6 2 3000000e 6 2 2000000e 6 2 1000000e 6 2 0000000e 6 1 9000000e 6 1 8000000e 6 1 7000000e 6 1 6000000e 6 1 5000000e 6 see section 3 7 1 evred 350 Mean of last 100 o satsave Set Scales 9000000023 Pray Moyes yar a IY Tiger AAA Aa 400 450 500 Time s Page 27 of 117 550 600 Issue 1 05 3 Driving your microK 3 1 Introduction The operator interface for the microK is provided through the touch screen and colour display The software is written in Microsoft s new C language and runs under the Windows CE operating system This provides a familiar and easy to use interface The buttons in the microK software have been sized and positioned to allow you to operate the instrument with your finger If numeric or alphanumeric data needs to be entered a soft keyboard window
69. et to 1234 initially but this should be changed before using the microK in a real measurement calibration application to ensure security see section 3 7 5 2 Enter the password to open the resistor database window Press New to create a new resistor entry in the database and enter data by pressing the ellipses button by each field Soen Page 14 of 117 Issue 1 05 TT WILKINS 1 au Resistor Resistor Name D Value WILKINS 1 99 999831 Manufacturer s Name Tinsley Serial Number 279509 Calibration Due 15 12 2008 New Delete Press OK to close the resistor window Connect the SPRT to be calibrated to channel 1 see section 4 2 for details on how to connect 4 wire PRTs and the reference resistor to channel 2 Press the Settings tab in the main window and disable channels 2 and 3 this will speed up measurements on channel 1 which we will be using by using the up down buttons by the Channel box to select these channels and pressing Disable Use the up down buttons to return to channel 1 Use the up down buttons by each box to select the required settings for the SPRT Single Multi Channel Settings Instrument Units z0 ometer Disable J Ohms Current mA Default PRT 1 0000 inversion B Samples per Read
70. f 117 Issue 1 05 7 The microK Technology The microK uses a number of new technologies and measurement techniques to achieve performance that was previously only available using AC resistance bridges for measuring the resistance of PRTs and separate high precision digital multi meters for measuring the EMF generated by thermocouples The concept for the core ADC technology was licensed from NPL the UK s national standards laboratory and operates under NPL s Technology Applied scheme NPL National Physical Laboratory Technology Applied 7 1 The ADC The ADC Analogue to Digital Converter in a precision instrument is the measurement engine Its performance is the starting point for achieving low measurement uncertainty The microK uses a completely new type of ADC which was designed specifically for this product It is based on the well established amp A sigma delta technique but uses multi bit feedback to achieve performance that is not achievable with conventional A ADCs In a conventional 2 A ADC the analog input signal is subtracted from the output of a 1 bit DAC before being filtered by a series of cascaded integrators The signal then passes to a 1 bit ADC that drives the DAC and forms a feedback loop Digital OUTPUT Filter VALUE Integrators nop DD Conventional A ADC SYSE Page 67 of 117 Issue 1 05 The extremely high gain of the cascaded integrators at low frequency
71. f electrical noise for example electrical supplies to furnaces The insulation in high temperature furnaces any that glow begins to conduct at higher temperatures This can cause high common mode voltages on any thermometer in the furnace Whilst the microK is designed to reject common mode DC and AC signals at both 50 and 60Hz it is good practice to minimise them It is common practice to use a metal equalising block in a furnace when performing comparison calibrations This should be connected to the safety earth of the electrical supply most furnaces designed for temperature metrology applications are fitted with a device to earth the equalising block Do not earth the SYSE Page 58 of 117 Issue 1 05 equalising block to the screen measurement ground terminals on the front panel of your microK as this is not connected to the safety earth of the electrical supply Provide a clean electrical environment in your temperature laboratory It may be useful to filter your electrical supply into the laboratory especially if other heavy electrical machinery is being used nearby on the same supply the microK has very good immunity to electrical noise conducted along the electrical supply but other equipment in your laboratory may be more sensitive Avoid using sources of electrical signals or noise in your laboratory examples include furnaces with triac controls especially those that chop the electr
72. g the conditions defined by previous SENSe commands This is equivalent to INIT followed by FETCh Example a microK that is connected to a short circuit on channel 1 and has been configured to make a voltage measurement using SENSe commands such as SENS CHAN 1 SENS FUNC volt and SENS VOLT RANG 0 1 will respond to READ with something similar to 1 70000000E 008 11 6 22 Command MEASure VOLTage Format MEASure SCALar VOLTage DC lt channel gt Initiates and reports a voltage measurement on lt channel gt using the voltage range specified note that there is no gap between the command and the channel number as this command makes use of the numeric suffices feature of SCPI described in section 11 3 This command is equivalent to SENS FUNC volt SENS CHAN lt channel gt and READ Example to initiate a voltage measurement on channel 3 use MEAS VOLT3 11 6 23 Command MEASure FRES REF Format MEASure SCALar FRESistance lt channel gt REFerence lt reference gt lt resistance range gt lt current gt Initiates and reports a resistance measurement on lt channel gt against a reference on channel lt reference gt using lt resistance range gt with sense lt current gt note that there is no gap between the command and the channel numbers as this command makes use of the numeric suffices feature of SCPI described in section 11 3 This command is equivalent to SENS FUNC fres SENS FRES REF Suissa Pag
73. hannel 8 1 2 1 Zero Ohms Check Start by applying a four terminal short circuit to channel 1 This involves shorting out the voltage sense terminals marked V and the current terminals market I and then making a single connection between these two set of terminals The objective is to ensure that none of the sense current passes along the wire between the voltage sense terminals This can easily be achieved using a single piece of un insulated wire SuSE Page 79 of 117 Issue 1 05 V V 4 Terminal Short Circuit Configure the microK to measure a Default PRT at 1mA against the internal 100Q reference on the 125Q range on channel 1 other channels disabled Set the units to Ohms and use 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Single tab and clear the statistic After the microK has collected at least 100 readings shown as Mean of last in the Single tab check that the Mean is less that 0 000004 4uQ i e 0 032ppm of the 1250 range and that the standard deviation S D is less than 0 00001 8 1 2 2 400 Q Internal Reference Resistor Connect a stable external resistance standard with a nominal value of 100Q to channel 1 Ideally this should be a DC or AC DC resistance reference standard with a recent traceable calibration certificate maintained at a constant temperature in an oil bath Configure the microK to measure a Default PRT at ImA against the inte
74. have a 0 123uV offset subtracted from voltage measurement on channel 2 will respond to CAL OFFS2 with 1 23E 07 11 6 32 Command CALibrate GAIN Format CALibrate GAIN lt polarity gt lt adjustment gt Adjusts the measurement system s voltage gain for lt polarity gt by the factor lt adjustment gt The parameter lt polarity gt must be either POSitive or NEGative The adjustment is only applied if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 The gain adjustment is stored as a floating point number and will therefore be subject to some rounding less than 0 12ppm of value Sors Page 110 of 117 Issue 1 05 Example for a microK that has been found to have a voltage gain for positive readings that is low by a factor of 1 000123 see section 8 2 3 the gain can be corrected using CAL GAIN POS 1 000123 11 6 33 Command CALibrate GAIN Format CALibrate GAIN lt polarity gt Reports the total calibration adjustment applied to the measurement system s voltage gain The parameter lt polarity gt must be either POSitive or NEGative Example a microK that has had a number of gain adjustments causing a total ratio adjustment of 1 000123 for positive readings will respond to CAL GAIN POS with 1 000123 11 6 34 Command CALibrate GAIN RESet Format CALibrate GAIN RESet lt polarity gt Resets the gain adjustment for the specified lt polarity gt to 1 T
75. he parameter lt polarity gt must be either POSitive or NEGative The gain reset is only implements if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 Example to remove all calibration adjustment set adjustment to 1 for positive voltages use CAL GAIN RES POS 11 6 35 Command CALibrate GPIB ADDRess Format CALibrate GPIB ADDRess lt gpib address gt Sets the GPIB address to lt gpib address gt The address must be in the range 0 30 inclusive The change is only made if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 Example to set the GPIB address to 21 use CAL GPIB ADDR 21 11 6 36 Command CALibrate GPIB ADDRess Format CALibrate GPIB ADDRess Sors Page 111 of 117 Issue 1 05 Example a microK with GPIB address 10 will respond to CAL GPIB ADDR with 10 Reports the GPIB address 11 6 37 Command CALibrate PASSword Format CALibrate PASSword lt old password gt lt password gt lt password gt Changes the password used to lock protect the calibration of the microK s measurement system This is initially set to 1234 but should be changed before using the microK for any critical or traceable measurement or calibration work The new password must be at least 4 characters in length and must be typed in identically twice in order to effect the change The change is only applied if calibration has
76. he thermometer s temperature to stabilise after each change in current as follows In the Setting tab press the ellipses button by Current mA Single Multi Channel Settings Instrument Units Ge Thermometer PIE ef Disable i Rt Rs Current mA 1 0000 ft ISPRT 1 Conversion Samples per Reading ITS90 lel Range Ohms 125 Reference Channel Channel 3 ao G 100 Reference Resistor ae g oe Readings in Rolling Statistics WILKINS 1 elf iS Zero Power Extrapolation Clear Zerc 1 0000 mA 2mA Custom 5mA 2 10mA x V2 Power Extrapolation OK Cancel In the current sequence window use the ellipses buttons to set each parameter bors Page 62 of 117 Issue 1 05 Settling Time s 120 Normal Current mA 1 0000 Alternate Current mA 0 5600 Readings at Each Current 100 p COLL OK Cancel Sequence The sequence defined by the parameters is shown at the bottom of the window in this case it comprises a 120s settling time 100 readings at ImA a 120s setting time 100 readings at 0 56mA a 120s settling time 100 readings at ImA Noe eS You can view the status of
77. hnique in which the Device Under Test and the Reference are successively switched into the same position in the measuring circuit This means that the stability of resistance ratio measurements is immeasurably small see section 7 4 SulSGh Page 115 of 117 Issue 1 05 13 Approvals The microK has been independently verified as complying with the regulatory requirements of the EU and FCC for electromagnetic compatibility and safety EU only 13 1CE Declaration European Community Electromagnetic Compatibility Directive 89 336 European Community Low Voltage Directive 93 68 The microK Precision Thermometry Bridge manufactured by Isothermal Technology Limited of Pine Grove Southport Merseyside PR9 9AG United Kingdom conforms to the requirements of the European Community Electromagnetic Compatibility Directive 89 336 and of the European Community Low Voltage Directive 93 68 13 2FCC Statement This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area may caus
78. ic and graphical form Multi displays all three channels in numeric form Settings allows you to configure the channels to perform the required measurement Instrument allows you to enter information on the thermometers and reference resistors used with the instrument into its database It also allows you to save load measurement data and instrument configurations in the database and to change instrument settings such as time date and the security password The main window opens with the Single tab selected 3 4 The Single Tab Select this tab to see a single channel in both numeric and graphical form SVS Page 30 of 117 Issue 1 05 single Multi Settings Instrument Channel a 1 o a Clear Graph 24 9998 Ohms 24 999794 Mean of last 100 24 9999500 24 9999000 24 9998500 24 9998000 Peal PON tal Pas i NPA PUR 24 9997500 24 9997000 24 9996500 24 9996000 50 100 150 200 250 300 Time f s The numeric display shows the last reading together with the mean and standard deviation of the most recent readings the number or readings in the statistics is set in the Settings tab If the zero power extrapolation feature is being used the mean and standard deviations are replaced by the Zero power Value and Uncertainty values and the Clear button is replaced by the Details button see section 6 The numeric and graphical outputs are updated a
79. ical supply part way through a cycle better controllers switch only at the zero crossing point to chop only whole cycles and mobile phones the microK is not significantly affected by mobile phones but other equipment may be more sensitive 5 3 Looking After Your microK Your microK is a precision electronic instrument intended for indoor use in a laboratory or office environment Nonetheless it has been designed to be as robust as is practical and will provide many years of service provided it is properly maintained We recommend that you return your microK to Isothermal Technology or one of our approved service centres on an annual basis for calibration Isothermal Technology has developed a calibration kit for the microK Contact Isothermal Technology or one of our appointed distributors if you wish to purchase a kit to calibrate the microK yourself The microK should require little maintenance between calibrations other than routine cleaning Under no circumstances should you use sharp or unsuitable objects such as ball point pens on the touch screen as this will lead to premature failure It is also a good idea to ensure that you have clean hands when using the touch screen You should ensure that you do not have contaminants such as adhesives or solvents on you fingers when touching the screen as these will be difficult to remove Sors Page 59 of 117 Issue 1 05 without damaging the screen You can fit a scr
80. ily intended to allow you to connect a USB flash drive store measurement results and transfer these to a PC The flash drive may also be used to backup the databases of thermometers reference resistors and instrument configurations for your microK Other USB devices such as a mouse keyboard keypad or USB hub may be connected to the Soen Page 10 of 117 Issue 1 05 USB port and used provided they utilise the standard class drivers provided with the Windows CE operating system incorporated in your microK On the rear panel of your microK you will find the electrical supply connector power switch fuse module plus the interface connectors that allow you to connect your instrument to a PC The RS232 and GPIB ports allow you to control the instrument and take measurements from a PC with your own software see sections 9 and 10 The command protocol employs the widely used SCPI format see section 11 for details The RJ45 Ethernet connector allows the microK to be connected to your network The USB B connector is used to load firmware during manufacture and should not be used during normal operation IEC 60320 1 Supply USB B Connector Power Connector Fuse unused On Off Ethernet RS232 GPIB Switch Connector Connector Connector Suissa Page 11 of 117 Issue 1 05 2 Making a Measurement Tutorials The operator interface is powered by the Windows CE operating system With the widespread use of Windows applicati
81. ired settings Single Multi Settings Instrument Channel Units Oe oe pee Thermometer 7 Default Thermocouple a Conversion Samples per Reading o ie pig pe Readings in Rolling Statistics je Reference Junction 0 00 C i The Conversion and Reference Junction setting are not important since we are only going to measure the output in volts Connect the thermocouple to channel 1 see section 4 5 for details on how to connect thermocouples and place the reference junction in an ice point reference Press the Single tab to see the measurements in numeric and graphical form Set the graph scales manually by making a note of the current Mean value and pressing Set Scales This opens the graph scales window Ensure that autoscaling is turned off press Autoscale to toggle autoscaling on off the status of autoscaling is shown by the adjacent indicator Use the ellipses buttons to set the y axis limits to be 0 5 uV above and below the current mean value Use the radio and up down buttons to set the x axis to 10 minutes Sors Page 26 of 117 Issue 1 05 Y Axis Channel ff Minimum 1 5e 06 Maximum 2 5e 06 e Autoscale X Axis Scale Minutes SE Time Units Seconds Minutes OK Cancel Pr
82. l Technology microK 100 09 P119 ITL261067 firmware version 1 14 11 6 6 Command RST Format RST Performs a reset equivalent to a power on reset of the measurement system firmware 11 6 7 Command SENSe FUNCtion Format SENSe FUNCtion lt function gt Selects the measurement function The parameter lt function gt must be one of the following valid SCPI parameters VOLTage DC l FRESistance RATio Example to set the microK to measure ratio use SENS FUNC RAT 11 6 8 Command SENSe FUNCtion Format SENSe FUNCtion Reports the current measurement function Sors Page 102 of 117 Issue 1 05 Example a microK set to measure voltage will respond to SENS FUNC with VOLTAGE 11 6 9 Command SENSe CHANnel Format SENSe CHANnel lt channel gt Selects the channel for the next measurement The channel is not actually selected until a measurement is started using either the INITiate or READ commands Example to select channel 2 for the next measurement use SENS CHAN 2 11 6 10 Command SENSe CHANnel Format SENSe CHANnel Reports the channel selected for the next measurement Example a microK set to measure channel 1 on the next measurement will respond to SENS CHAN with 1 11 6 11 Command SENSe FRESistance REFerence Format SENSe FRESistance REFerence lt reference channel gt Selects the reference channel for the next resistance measurement made The channel is not ac
83. librated if you only want to make a resistance ratio measurement between two channels Reference Junction box thermocouples only This contains 0 C 0 01 C and a list of any input channels that have been configured to measure temperature Choose 0 C or 0 01 C if you are using an external reference junction in an ice point bath or water triple point respectively Choose one of the measurement channels if you want to measure the temperature of the reference junction with a SYSE Page 36 of 117 Issue 1 05 thermometer sensor on that channel The software will not allow you to use a thermocouple channel as the reference junction sensor to avoid circular dependencies You must specify a thermometer sensor for the reference junction channel that includes temperature conversion otherwise it will not appear in the Reference Junction box Units box Use the up down buttons to select the required units The base units resistance ratio Rt Rs for PRTs or thermistors and Volts for thermocouples are always available Ohms will also be available for PRTs and thermistors if the value of the reference resistor is available Reference Resistor not set to Uncalibrated If the thermometer sensor chosen has a temperature conversion specified then temperature units C F and K are also available Current box Press the ellipses button to change the sense current Use the buttons in the window that then opens
84. lity However small differences between the thermal EMFs generated by the devices used to make these reversals on each channel mean that the zero offset needs to be checked for each channel Once the zero offsets have been checked adjusted it is only necessary to check the span on one channel since this part of the measurement system is common to all the channels 8 1 3 1 Zero Voltage Offsets Short out the 4 measurement terminals on all 3 channels using a piece of un insulated copper wire for each channel SYSE Page 81 of 117 Issue 1 05 V Configure the microK to measure a Default Thermocouple with units set to Volts all 3 chanels Use 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Multi tab and clear the statistics for all 3 channels After the microK has collected at least 100 readings shown as Mean of last in the Multi tab check that the Mean for each channels is less than 0 00000025 0 25u V and that the standard deviation S D does not exceed 0 00000002 0 02u V 8 1 3 2 Voltage Span Check Connect a stable low noise voltage source with a nominal value of 50mV to channel 1 of the microK using low thermal EMF wire and connectors copper or an alloy such as tellurium copper that has a high copper content and low thermal EMF to pure copper Brass connectors must NOT be used V Voltage Source V Configure the microK to measure a Default Thermocouple with
85. m the operator interface It would be very difficult to make this information available through SVS Page 99 of 117 Issue 1 05 SCPI commands so it is not possible to request a measurement in temperature units using SCPI commands However it is possible to set up measurement s using the operator interface and then to access the results using SCPI commands To do this simply setup your microK to make the required measurement from the front panel see section 2 2 for an example of how to do this and then when the microK is running and making the required measurement send the command READ lt channel gt Where lt channel gt is the number of the channel from which you require the measurement The microK will then echo the measurement the next time a results is available for that channel It will report the value and units for example 9 87654321E 010 C Where units X for ratio R for ohms for Kelvin C for C F for F If the microK detects that the requested channel is not enabled it will report not enabled The READ Command can be cancelled in order to allow measurements from another channel to be requested by send the command ABORt Sors Page 100 of 117 Issue 1 05 11 6 4 SCPI Commands The microK supports the following commands IDN RST SENSe FUNCtion ON FUNCtion ON CHANnel CHANnel FRESistance REFerence REFerence RANGe UPPer RANGe UPPer
86. ment in the system into which the SPRT and Reference Resistor are switched alternately Resistor Reference Amplifier Substitution Measurement Topology This adds complexity and cost to the design but ensures that there is no change to the common mode signal between the measurement of the reference resistor and the thermometer This approach would normally however increase the demands on the current source In the conventional topology the current is common to both the reference resistor and the thermometer In the substitution topology the voltage at the output of the current source changes between the measurement on the SPRT and the Reference Resistor and the current source Svea Page 74 of 117 Issue 1 05 must accommodate this change without any significant change to the sense current The current source in the microK has a very high output impedance such that the sense current will not change significantly between the measurement of the reference resistor and the thermometer In addition the whole measurement system is actively guarded so that both the voltage at the output of the current source and the common mode voltage across the device being measured do not change Resistor Reference E Guard Amplifier Guarded Measurement System The Guard Amplifier senses the potential at the top of the measurement system and drives the opposite end in order to maintain it at gro
87. mmand keyword with keywords being separated by colons To simplify the description of the SCPI commands the notation represents levels in the tree using horizontal indentations with the root node being the left most column For example the microK includes the following command structure Sore Page 94 of 117 Issue 1 05 SENSe FUNCTION gt CHANNEL FREsistance REFerence REFerence RANGe RANGe READ CALibrate CURRent OFFSet OFFSet A valid command is formed by following the tree structure from a root node until a node is reached with no further nodes below it for example in the above command tree we may use SENSe FRESistance REFerence Keywords can be shortened to the first four letters or 3 if the last letter is a vowel To indicate this the notation uses upper case to indicate required letters and lower case to indicate optional letters NB all commands are case insensitive For example valid forms of the above command include Sense Fresistance Reference SENS FRES REF Sense fresistance REF To shorten the commands default optional keywords are enclosed in square brackets and may be omitted For example in the case of the command MEASure SCALar VOLTage DC Valid forms of this command include MEAS VOLT MEASURE SCALAR VOLTAGE DC Sors Page 95 of 117 Issue 1 05 11 3SCPI Numeric Suffices In order to support multiple input channels commands can include numeric
88. nce cece cceeeeccceeeeeeeeees 105 11 6 16 Command SENSe RATi0 REFerence oncer 105 11 6 17 Command SENSe RATIO RANGE cece cceeeccccceeeeccceeeeeeeeees 105 11 6 18 Command SENSe RATI0 RANGE eerren 106 11 6 19 Command INI Tiate ii cc cecccccceeeeccseeesscceseesescsseeeeseesees 106 11 6 20 Command FETCH uu ieia a eii aiii ii iiia 106 11 6 21 Command READ 0 ce ccccccccceeeeccceeeescccseesescsseeneeseeees 107 11 6 22 Command MEASure VOLTA age 0000 0 eeeeeeceeeeneeeeseeneeeeeeees 107 11 6 23 Command MEASure FRES REF 0 c cece ceeeeccceeeeeeeeees 107 11 6 24 Command MEASure RAT REF cc cceecccceeeeeccceeeeeeeeees 108 11 6 25 Command CURRED ccecccccceeeeccsceeescccseeeseceseeesseseees 108 11 6 26 Command TEST CURRent 0 cece cc eeeeccceeeescceeeeeeeeees 108 11 6 27 Command CALibrate CURRENt ccc ceeecccceeseeecceeeeeeeeees 109 11 6 28 Command CALibrate REFerence 0 c ccceeeccccceeeeccceeeeeeseees 109 11 6 29 Command CALibrate REFerence cccceecccceeeesccceeeeeeeees 109 11 6 30 Command CALibrate OFFSet cccccccceeecccceeeeeccseeeeeeeeees 110 11 6 31 Command CALibrate OFFSet ccccccceeecccceeessccseeeeeseees 110 11 6 32 Command CALibrate GAIN ccccccceecccccceseeccceeeseecceeeeeeeeees 110 11 6 33 Command CALibrate GAIN 0 cccccceecccceeesccceeesccceeeeeeseees 111 11 6 34 Command CALibrate GAIN RESet c cece ceeee
89. nce channel for the next resistance ratio measurement use SENS RAT REF 2 11 6 16 Command SENSe RATio REFerence Format SENSe RATio REFerence Reports the channel selected as the reference channel for the next resistance ratio measurement Example a microK set to use channel 2 as the reference in the next resistance ratio measurement will respond to the command SENS RAT REF with 2 11 6 17 Command SENSe RATio RANGe Format SENSe RATio RANGe UPPer lt vresistance range gt lt current gt Sets the range for the next resistance ratio measurement The range is determined by the voltage range of the measurement system 0 125 or 0 5V and depends on the sense current used The current parameter is the current you intend to use in the measurement this may not be the same as the present value of sense current that is set with the CURRent command The 2 resistance ranges available with the microK are SYSE Page 105 of 117 Issue 1 05 resistance range 0 125V current resistance range 0 5V current The resistance range specified should be the higher of the maximum PRT resistance and reference resistor since the measurement system has to measure the signal across both to determine their ratio Example to set the microK to measure the resistance ratio of a PRT that has a maximum resistance of 130Q with a 100Q reference resistor with a ImA sense current use SENS RAT RANG 130 1 This will set the micr
90. nce measurement have the effect of ensuring an intrinsically stable zero with time and temperature The voltage at Sors Page 76 of 117 Issue 1 05 the amplifier input when measuring a short circuit will be the same whichever current direction is used The process of averaging the measurements therefore yields zero with uncertainty determined by the system noise In a similar way the substitution topology means that the measurement system is also inherently stable at unity ratio since the voltages measured for a reference resistor and thermometer of the same value will be identical There is after all no difference between these two measurements apart from the fact that they are taken at slight different times The system noise will again determine the uncertainty of this unity ratio measurement 7 8 Eliminating Self Heating Effects Although the sense currents used with SPRTs are small they can still generate self heating errors of several mK The most accurate SPRTs typically have very lightly supported elements so the self heating effect is ironically worst in those SPRTs designed for the most accurate measurements The microK includes individual keep warm current sources for each of the three input channels These replace the sense current when a channel is not being measured and ensure that the power dissipated in an SPRT remains constant The most accurate measurements with an SPRT involve measuring its r
91. nel Ifa replacement fuse fails immediately contact your local service agent DO NOT replace with a higher value Always use the power cord supplied Your sales outlet can provide a lead suitable for your country This equipment is for use in moderate climates only NEVER use the equipment in damp or wet conditions Avoid excessive heat humidity dust amp vibration Do not place liquid filled containers on the equipment Do not use where the equipment or any associated accessories may be subjected to dripping or splashing liquids Ensure that the power switch is easily accessible to allow the unit to be switched off The equipment weighs 13kg use the handles provided Always disconnect the equipment from the electrical supply and any ancillary units before moving Ensure that tabletop equipment is placed on a solid level surface which is able to support its weight and that of any attached accessories Ensure all cables and wires are routed safely to avoid tripping also to avoid sharp bends and pinches Clean only with a damp cloth Do not wet or allow moisture to penetrate the unit Do not use solvents See section 5 3 for details of cleaning procedure The product should be subjected to regular in service inspections as required by local regulations a yearly interval is suggested Sors Page 8 of 117 Issue 1 05 Verify that the supply cordset is undamaged and that the enclosure is bonded
92. ng technique we are able to reduce voltage noise at the expense of current noise by using a number of amplifiers connected in parallel increasing n The microK uses a large array of amplifiers in order to reduce the voltage noise to a level that was only previously achievable using AC resistance bridges 7 3 Buffered Switching In instruments such as the microK switching devices are used to route the currents and signals during the measurement process Ideally these should have zero on resistance and infinite off resistance The on state resistance does not normally lead to significant measurement uncertainty but off state resistance or leakage is much more critical In a typical arrangement a 1mA sense current applied to a PRT a leakage current of only 100pA would lead to a measurement error of 0 1ppm Mechanical relays designed for signal switching can provide adequately high off state resistance such that they contribute negligible measurement uncertainty but they offer very limited reliability Semiconductor devices offer very high reliability but off state leakage typically leads to significant measurement uncertainty if used to switch signals directly For this Sors Page 72 of 117 Issue 1 05 reason instruments like the microK have traditionally used mechanical relays in order to achieve performance at the expense of reliability The microK uses a buffered switch technology designed to eliminate the effect of the
93. nnel 1 and connect both the sense inputs to the red current terminal V Send the command TEST CURR 1 to your microK from Hyperterminal this forces the microK to source 1mA on channel 1 Measure the current and then type in the command CAL CURR current where current is the measured value Now type in TEST CURR 1 again to update the current source The ammeter should now read 1mA 0 0003mA Check the other current ranges by typing in the following commands and checking that the current is within the given limits command current limits TEST CURR 0 1 0 09975 to 0 10025 mA TEST CURR 10 9 975 to 10 025 mA TEST CURR 0 1 0 09975 to 0 10025 mA TEST CURR 1 0 9975 to 1 0025 mA TEST CURR 10 9 975 to 10 025 mA Sore Page 84 of 117 Issue 1 05 8 2 1 1 Calibrating the 400 Q Internal Reference Resistor Connect a stable external resistance standard with a nominal value of 100Q to channel 1 Ideally this should be a DC or AC DC resistance reference standard with a recent traceable calibration certificate maintained at a constant temperature in an oil bath Configure the microK to measure a Default PRT at ImA against the internal 400Q reference on the 500Q range with channel 1 other channels disabled Set the units to ratio Rt Rs with 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Single tab and clear the statistics After the microK has collected at least 100 readings shown a
94. nt number and will therefore be subject to some rounding less than 0 12ppm of value Example if the value of the internal 100Q reference has been measured as 100 00123 the new value can be assigned to it using CAL REF204 100 00123 11 6 29 Command CALibrate REFerence Format CALibrate REFerence lt reference gt Used to report the calibrated value of the internal lt reference gt resistor used by the microK to calculate resistance SVS Page 109 of 117 Issue 1 05 Example a microK with an internal 25Q reference having a calibrated value of 25 01234 will respond to CAL REF203 with 25 01234 11 6 30 Command CALibrate OFFSet Format CALibrate OFFSet lt channel gt lt offset gt Adjusts the voltage offset for lt channel gt used when making voltage measurements The offset range is 2uV attempts to apply an offset greater than this will be ignored The adjustment is only applied if calibration has already been unlocked using the CALibrate UNLock command see section 11 6 38 The offset is stored as a floating point number and will therefore be subject to some rounding less than 0 12ppm of value Example to subtract an offset of 0 123uV from voltages measured on channel 3 use CAL OFFS3 0 123 11 6 31 Command CALibrate OFFSet Format CALibrate OFFSet lt channel gt Reports the offset subtracted from voltage measurements on lt channel gt Example a microK that has been calibrated to
95. oK is ready to respond There will be a delay from receiving the command to attempting to respond depending on the command requesting data involves a short delay but requesting a measurement may take up to 2s and whether the microK is busy processing other commands if measurements are being requested via the front panel operator interface or via the RS232 interface Sors Page 92 of 117 Issue 1 05 The microK has a 254 byte receive buffer If the command exceeds this length it will be truncated 10 1GPIB Address The microK behaves as a GPIB Peripheral and can have an address in the range 1 to 30 inclusive The factory default address is 10 but this can be changed using SCPI commands see section 11 6 35 sent on the GPIB or RS232 interface or through the operator interface see section 3 7 7 10 2Establishing a GPIB Connection Connect your microK to a GPIB Controller using a standard straight through GPIB cable Send IDN to the GPIB address of the microK see section 10 1 terminated with a Line Feed see section 11 1 for acceptable terminators the microK should then respond with a string in the form Isothermal Technology microK 100 09 P110 firmware version 1 16 This confirms that you have successfully established a GPIB connection with your microK SVS Page 93 of 117 Issue 1 05 11 SCPI Command Set The command format and protocol used by the microK is based on the SCPI Standard Commands for Pr
96. oK to the 0 5V range 11 6 18 Command SENSe RATio RANGe Format SENSe RATio RANGe UPPer Reports the range for the next resistance ratio measurement at the present sense current set using the CURRent command The current used to calculate the range may be different from that specified when the range was set using the SENSe RATio RANGe command The reported range is the actual range for the measurement system at the present sense current Example a microK that has had its resistance ratio range set using the command shown in section 11 6 17 but has its sense current set to 10mA would respond to the command SENS RAT RANG with 50 000000 11 6 19 Command INITiate Format INITiate MMediate ALL Initiates a measurement using the conditions defined by previous SENSe commands The measurement is made immediately but not reported Example to initiate a voltage measurement that has been defined with SENSe commands such as SENS CHAN 1 and SENS FUNC volt use INIT 11 6 20 Command FETCh Format FETCh SCALar Reports the result of the last measurement made Sors Page 106 of 117 Issue 1 05 Example a microK that has made a measurement on a short circuit connected to channel 1 using the commands shown in the example in section 11 6 19 will respond to FETC with something similar to 1 70000000E 008 11 6 21 Command READ Format READ SCALar Initiates and reports a measurement usin
97. ogrammable Instruments standard This was developed to provide a consistent command language for all types of programmable instruments The objective was to reduce the development time required by users of these instruments by providing a consistent programming environment through the use of defined messages instrument responses and data formats Further information on SCPI can be obtained from the SCPI Consortium http www scpiconsortium org 11 1Command Terminators SCPI commands are ASCII American Standard Code for Information Interchange character strings If sent to the microK s RS232 interface these should be terminated with a Carriage Return character ASCII character 13 Responses from the microK on the RS232 interface are always terminated by a Carriage Return character If commands are sent to the microK s GPIB port they can be terminated by a Line Feed character ASCII 10 Carriage Return character ASCII 13 EOI condition by pulling the EOI line low during the last character of the ASCII string or any combination of these Responses from the microK on the GPIB interface are always terminated by a Line Feed character the microK does not assert EOI at the end of a response 11 2SCPI Command Structure Commands are arranged in a hierarchical tree similar to directory trees used in personal computers SCPI uses a defined notation to represent the command tree structure Each node in the tree structure is a co
98. ons on PCs driving your microK should be fairly intuitive As with most Windows applications it is possible to navigate your way through a process using a number of different paths so rather than describe each window and the function of each button and then leaving you to work out how to operate the instrument we provide you with a number of tutorials that illustrate common applications Even if these do not describe your application it is worth working through one of them since it will provide you with a broad understanding of the extensive features available on your microK A traditional description of the function of all the features provided by the operator interface is given in section 3 2 1 Fixed Point Calibration of an SPRT Using Zero Power Extrapolation Calibrating an SPRT using fixed point cells offers the lowest possible calibration uncertainty The process involves measuring the resistance of an SPRT with respect to an external reference resistor whilst at a number of temperatures by immersing it in a number of fixed point cells and then using that information to generate calibration data for the thermometer The reference resistor should be a DC or AC DC resistance reference standard maintained at a constant temperature in an oil bath or similar resistor maintenance system The sense current used to measure the resistance of a PRT for example the ImA used with a 25Q SPRT causes a small but significant amount of self
99. pm voltage accuracy with a DAC would not be feasible in this sort of product it is possible to achieve the corresponding timing accuracies buffer Integrators input gt Digital Filter 5 Bit PWM DAC Multi Bit 2 A ADC OUTPUT VALUE Sors Page 68 of 117 Issue 1 05 The timing demands of the PWM DAC are however far from trivial The digital filter has to work at the X A ADCs clock rate In the microK this digital part of the X A ADC is implemented in a fast FPGA which provides both the digital filter that decimates the DAC output to extract the converted value and controls the feedback DAC The full scale pulse width on the PWM DAC is only 10us so the lt 0 1ppm linearity of the microK100 corresponds to a timing accuracy of lps or about the time it takes for the electrical signals in the control system to travel 0 3mm It might appear that the reduction in quantisation noise from using multi bit feedback in a X A ADC would be directly proportional to the ADC DAC resolution However the reduced differential gain inherent in the higher resolution DAC greatly improves loop stability too This allows the use of more orders of integration and higher loop gain giving a disproportionate improvement in quantisation noise With the 5 bit system used in the microK the quantisation noise is reduced by a factor of 600 so that the performance of the microK is not limited by the X A ADC technique but by the semiconductor
100. polated value x arising from the noise defined by the standard deviation calculations associated with the data sets is dx ie Wy sw a 2 72 dx is if dx i Un zU 2 72 dx is ii The combined uncertainty reported by the microK is therefore 1 4 2 4 74 2 a2 aur lius l2 l4 As we would expect the above equation predicts that the uncertainty of the extrapolated result increases as i2 approaches ij The equation allows us to investigate the optimum ratio between i and iz For a resistance bridge such as the microK the noise and therefore the uncertainty of measurement will be SVS Page 65 of 117 Issue 1 05 inversely proportional to the sense current used So if we let i2 ki then uz u k Substituting into our uncertainty equation we get Uy 1 ae a If we differential this with respect to k and set this equal to zero in order to find a minimum for u we get 2k 3k 1 0 The relevant solution to this equation if k 0 55938 This means that the optimum ratio between the alternate and normal current is not 1 V2 but 0 56 This applies to all resistance bridges but just the microK The improvement in uncertainty in going for 1 V2 to 0 56 is only 13 because u is fairly insensitive to k for values near to 0 56 For convenience a ratio of 0 5 is a sensible choice as there is less than a 2 degradation in uncertainty between this and the optimum value Sors Page 66 o
101. re version is found you will be offered the opportunity to upgrade 3 7 5 2 Update Software and Firmware The microK can only update either the firmware or software on each restart If you wish to upgrade both copy both files to the root directory of a USB flash drive connected to the front panel USB connector and invoke the update software feature twice The firmware will be updated first 3 7 6 Change Password Press the Change Password button to change the security password see section 3 11 for details of password protected settings A window will then open to allow you to change the password Sore Page 45 of 117 Issue 1 05 Old Password New Password Jv Confirm New Password OK Cancel Enter the old password and the new one twice to ensure that it has been correctly entered Press the ellipses buttons by each of the password boxes to open an Alpha Numeric Keyboard window and enter the relevant password Your microK is shipped with the password set to 1234 This should be changed for security reasons before using your instrument in earnest 3 7 7 Port Settings Press Port Settings to view and change the microK s GPIB or IP address the RS232 baud rate is fixed and cannot be changed RS232 Baud Rate GPIB Address tT Q lt Ethernet IP Address ft Static IP Address Q 10 Bl ee OK
102. read it through at this time so suggest you read the safety section below take one of the tutorials in section 2 and then refer back to the manual using the list of contents to find additional information as required 1 1 Unpacking Your microK product should comprise the following items microK precision thermometer power lead suitable for your country this user manual If any item is missing or damaged please report this immediately to your supplier If possible we recommend that you retain the packaging material in case you need to return the instrument for calibration or service since it has been designed to ensure that your microK is properly protected during transportation 1 2 Safety The microK is a precision instrument designed for use in a laboratory It complies with the requirements of safety standard EN61010 1 2001 and is therefore safe to use in laboratory or light industrial environments It is not intended for use outdoors or in extreme environments refer to specification in Section 12 The microK is likely to be connected to thermometer sensors in use and the operator should take care to ensure that the complete system is safe For example metal sheathed thermometers may be connected to the microK and then placed in a furnace powered from a 230V electrical supply Single fault conditions in such a furnace could lead to the thermometer wires and the front terminals of the microK to which they are connected b
103. rmometer Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter edit a name The Shift key toggles the alpha keys between upper and lower case Serial Number box This box contains the serial number of the selected thermometer Press the ellipses button by the box to open an Alpha Numeric Keyboard window and enter edit a serial number The Shift key toggles the alpha keys between upper and lower case Calibration Due box This box contains the date when calibration is due for the selected thermometer Press the ellipses button by the box to open a date entry window and enter a date The ellipses buttons by the Day Month and Year boxes in the date entry window open a Numeric Keypad window Dates are checked for validity including leap years for dates up to 31 December 2099 eS Page 40 of 117 Issue 1 05 Thermometer Type box This box contains the type of thermometer PRT Thermocouple or Thermistor If you are creating a new thermometer entry use the up down buttons to select the thermometer type Min Temperature box This box contains the minimum operating temperature for the selected thermometer Press the ellipses button by the box to open a Numeric Keypad window and enter the minimum operating temperature for the thermometer Max Temperature box This box contains the maximum operating temperature for the selected thermometer Press the ellipses button by the box to open a Numeric Ke
104. rnal 400Q reference on the 500Q range on channel 1 other channels disabled Set the units to Ratio Rt Rs and use 1 sample per reading and 100 readings in the rolling statistics see section 3 6 Select the Single tab and clear the statistics After the microK has collected at least 100 readings shown as Mean of last in the Single tab check that the Mean agrees with the expected value within 1ppm of value half of the 10 year specification limit and that the standard deviation S D is less than 0 000000100 SYSE Page 80 of 117 Issue 1 05 8 1 2 3 100 Q Internal Reference Resistor Repeat the procedure for checking the 400Q internal reference see section 8 1 2 2 but configure the microK to measure a Default PRT at 1mA against the internal 100Q reference using the 125Q range on channel 1 The Mean should agree with the expected value within 1ppm of value with the standard deviation S D being less than 0 000000200 8 1 2 4 25 Q Internal Reference Resistor Repeat the procedure for checking the 400Q internal reference see section 8 1 2 2 but configure the microK to measure a Default PRT at 1mA against the internal 25Q reference using the 125Q range on channel 1 The Mean should agree with the expected value within 1ppm of value with the standard deviation S D being less than 0 000002000 8 1 3 Voltage Measurements The automatic input reversal of used by the microK when measuring voltage provides good zero stabi
105. s it is possible to reduce voltage noise at the expense of current noise but for any sensible system the voltage noise cannot be reduced much below InVHz At this level the noise is a significant source of uncertainty in typical temperature metrology applications so that users would need to filter average the readings for many minutes in order to achieve their target uncertainty The best AC bridge designs use noise impedance matching to minimise the noise contribution of the semiconductors used in the amplifier Since the waveforms in an AC bridge are sinusoidal a transformer can be used at the input to the amplifier to reduce input noise at the expense of voltage noise AMPLIFIER n we z aoe SPRT OUTPUT INSTRUMENT Noise Impedance Matching in an AC Resistance Bridge The transformer reduces the voltage noise referred to the input by the turns ratio n Correspondingly it increases the current noise by a factor of n By increasing n it is possible to reduce the voltage noise at the expense of increased current noise There is clearly an optimum value for n and this occurs when the noise impedance which is defined as the ratio of the voltage to current noise Sors Page 70 of 117 Issue 1 05 V in is matched by the transformer to the input impedance R This occurs when In the above example v 2nVHz i 0 2pAHz R 250 this occurs when n 20 In which case
106. s Mean of last in the Single tab record the Mean value and check that the standard deviation S D is less than 0 000000100 Calculate the value of the internal resistor from R400 exernal reference ratio Adjust the value assigned to the internal 400Q reference resistors by typing in the command CAL REF205 R400 The value entered can be read back using CAL REF205 Check the new value assigned to the internal 400Q reference resistor see section 8 1 2 2 8 2 1 2 Calibrating the 100 Q Internal Reference Resistor Repeat the procedure for calibrating the 400Q internal reference see section 8 2 1 1 but configure the microK to measure a Default PRT at 1mA against the internal 100Q reference on the 125Q range with channel 1 the standard deviation of the measurement should be less than 0 000000200 The command to adjust the value assigned to the 100Q internal reference is CAL REF204 R100 Where R100 is the value calculated for the 100Q internal reference SYS Page 85 of 117 Issue 1 05 8 2 1 3 Calibrating the 25 Q Internal Reference Resistor Repeat the procedure for calibrating the 400Q internal reference see section 8 2 1 1 but configure the microK to measure a Default PRT at 1mA against the internal 25Q reference on the 125Q range with channel 1 the standard deviation of the measurement should be less than 0 000002000 The command to adjust the value assigned to the 25Q internal reference is CAL REF203
107. s new readings are made The time between readings depends on the settings for that channel and any other channels that are also enabled This can vary between 2 seconds and 5 minutes The sample time for each channel is 2s so if all three channels are enabled each channel will be updated every 6s Channel box Use the up down buttons by the Channel box to select the channel you wish to view Alternatively press the ellipses button to open a numeric entry window and select the channel directly The ellipses button is particularly useful when the microK is used with microsKanner multiplexers which can provide up to 90 expansion channels You can only view channels that are enabled so if a channel is disabled in the Settings tab it will not appear in the sequence and will not be measured This means that the up down buttons have no effect if only one channel is enabled Clear Graph Press Clear Graph to clear the graph and re start the autoscaling feature This can be used to eliminate the effect of a large transient result SYS Page 31 of 117 Issue 1 05 perhaps caused when changing connections to the thermometer on the autoscaling function Clear button Press Clear to clear reset the statistics If the microK is configured to perform a zero power extrapolation on the selected channel the clear button is replaced by a Details button see section 6 for further details on this feature Set Scales button Press Set Scale
108. s to open a new window and set the x and y axes for the graphical output Y Axis X Axis Channel Scale Minutes oe eee Minimum Time Units 0 Seconds Maximum Minutes 10 Autoscale S In this window use the up down buttons by the Channel box to select the channel whose scales you wish to change the window opens with the currently displayed channel selected Use the radio buttons to select either Seconds or Minutes as the units Use the up down buttons by the Scale Minutes box to change the x axis time scale the same x axis scale is used for all channels Or press the ellipses button to open a Numeric Keypad window and enter the required scale directly Any value between 1 second and 1000 minutes inclusive may be used Use the ellipses buttons by the Minimum and Maximum boxes to open a Numeric Keypad window and set the y axis scale Alternatively press Autoscale to scale the y axis so that it will show all the readings The indicator by the Autoscale button shows whether autoscaling is active SYSE Page 32 of 117 Issue 1 05 Start Save button Press Start Save to record all the measurements being made You will then be offered the choice buttons of storing the data to the Internal memory solid state drive or an External USB flash drive Data stored to the internal memory is preserved when power is removed and can subsequently be transferred
109. sscsssesscsscsesssssssessessessscssessesessssssnessessesssessesssssessesssesee 83 8 2 1 Calibrate Master Current Source cccccceeeeeeeeeseseeeesenesserenees 84 8 2 1 1 Calibrating the 400 Q Internal Reference Resistor 85 8 2 1 2 Calibrating the 100 Q Internal Reference Resistor 85 8 2 1 3 Calibrating the 25 Q Internal Reference Resistor 86 8 2 2 Calibrating Voltage Zeros ec ee esseceeseneeeeeeneeecessneeeeseeneeeeeenaes 86 8 2 3 Calibrating Voltage Spano ee eeeecessseeeeeeeneeeceesteeeeseseeeeeenaes 87 9 RS232 INTERFACE scciccee sete ea lee ee tee 89 9 1 Establishing an RS232 Connection ccscccssscssccssesssssssscessssssssssssescssssessssssesesssssseees 89 10 GPIB INTERFACE ox since 5 fcccetecte tess eectses ec hel eid 92 10 1 GPIB Addres ssssticsscccssscccscosssecesoncshesasebesecesetesssnsecevevedsesecesessesvessivocsvevasceseesesenesetessessoese 93 10 2 Establishing a GPIB Connection eessserseseesesesosoesoeoesesoeeesorsesocsesesossoroesesosoesoeoeoesoeose 93 11 SCPI COMMAND SET sesseececceceeceenennnnnnsseeeeeeeeeeees 94 11 1 Command Terminators c ccsssccssssscssssscsssscsssccsssccssssssssssssssssssssssssssssssssscssssssssssees 94 11 2 SCPI Command Structure ccsssscsssscsssscscsssscsssscssssccssssscsscscsssscssssccsssscsssssssssscssscecs 94 11 3 SCPI Numeric Sutlices ccccssssescssssnscssesscseesscss
110. ssessscsscsscecsncssssnessesssssssssessessessnsssssesssessesscssessessssssessessosssessess 28 3 2 The Start Up Window sccscsscssssssssssssssscssssssssscsssscsnescsscessssesssscssessessssssessessosssessess 28 3 3 The Main Window sccsssssssscsscsssssssssssssscssssscsssscesssssnessssessssssssssssssessssssssessossseseess 29 3 4 The Single Tabies ccssassnsssscsacensessonsscossasccssenctasanssncoescssessssccedecnsvaceraceneseasacsonssascosoesoasssnsens 30 3 5 The Multi Tab 0 cssssccscsssssscsscsscnsescsssssessncsssessscsscsssscsnsssessesssssssssessessessssssessossosssessess 33 3 6 The Settings Tab ccscscccsssssssscsscssnsssssnsssesssssssssessssssssnescessesssessessessessessssssessessosssesness 35 3 7 The Instrument Tab cscssssscsscssssssssssscsessssssssssssssssssesssssesssessesssssessessssssessessessnesess 39 SEL Edit Thermometers eeror at re ae e a ERETTE 39 3 12 Edit RESISCOTS e era a e iW iaeed es sha daatestsdasescstenenetdes 42 I3 Cali Drain seatt a e a a A 44 3 74 Restart Softwaren aoet epee aooiee dete va i E EE EEE E 44 3 9 Update SOTware 3 2 vo succes sodgeedecnce cevenet aeeensdestansandsounntedechtesoteendss 44 3 7 5 1 Update FIFMWare ics scistesschecsesdvaiesacacsseesedeunsweasoucdasstrers 44 3 7 5 2 Update Software and Firmware ssessesseseeseesessesssesee 45 FVO Chan ge Pass word ieren eroto nE Erea Ee EEEE E iah 45 Dle POrt SEIN GS ceiseelece Sscscteata
111. teuctorsedsatavesteevasdadaeciuatcuwsnssveseobgeletestonas 46 3 7 8 Set Date and Time ire e o ea e a E aa aaa 47 3 49 Backup Data sist noer rae A A A E a e aa S 47 3 710 Cleat Data Piles iieri i renne E E Enia 48 3 7 11 Backup Configuration seisoin idia aaea taas 48 3 7 12 Load Configuration eeeesseseeeesseeesressseresssreersereesssreesssrreeseere 49 3 8 Using the Thermometer Database sesereeseseesesosoesoroeseeoeseseesesoesesososseseeoesosossesosossosoeessoeose 49 3 9 Using the Reference Resistors Database soesoesoosossoseoesossoesoseoesossoesoesossoessesoesosesessesse 50 Sors Page 2 of 117 Issue 1 05 3 10 Saving Instrument Configurations cccsccssssesscsssssessssssscscssssssesssssssssessssseesesees 51 3 11 Password Protection of Key Settings cscscsssscssscssessssscsscesesessssssssesssssscssessssseees 51 4 CONNECTING THERMOMETER SENSORS eeeeeeeeeseeseee 52 4 1 The Cable Pod Connectors sscscsssssscssccsssssssscsssssssssssssssssssssssssescsssssssessessessseees 52 4 2 Connecting PRIS 4 Wite sssccsiccsceccccdecssccccconsvekssossenstonstescsseascesavesesstsssecescvescnescssseccsotssnetes 52 4 3 Connecting PRIS 3 Wire ssciiesssseicsacdocssscseconcectsonsseccssaiee cevagedbessoccescssvesssonacossvocsecscsessseseee 53 4 4 Connecting PRTS 2 Wire scsciccsciccsscccisncevorssoacsencvecsodscotecseccvugisoserecerdessovseionedecstecrecsiconseas
112. thermal Technology 259 35 Serial Number Max Temperature C 66032_123 i 961 78 Calibration Due 15 12 2008 ate tT TS90 New Delete Coefficients Conversion e g Press Coefficients and enter the calibration coefficients for the SPRT by pressing the ellipses buttons by each field and entering the data in the numeric entry window that appears Conversion Name Conversion Type ITS90 ITS 90 R 0 01 25 4956321 Coefficients for T lt 0 01 C Coefficients for T gt 0 01 C a 0 0 00029667298 b P b 2 3806071e 05 AA AA 3 0497121e 06 d 100 OK w660 323 0 CEOE As SPRTs PRTs drift during use the proportional change in resistance is substantially the same at all temperatures If you periodically measure the SPRTs resistance at the water triple point 0 01 C and enter this value into this coefficients windows you will improve measurement uncertainty significantly Press OK to close these windows and return to the main window In the Instrument tab press Edit Resistors Suissa Page 21 of 117 Issue 1 05 Single Multi Settings Instrument Edit Thermometers RS Edit Resistors Calibration Restart Software Update Software Change Password System Calibration x Set Date and Time Backup Data
113. this to the alternate current whilst monitoring the results in the Single tab which will show the settling characteristics of the thermometer graphically Press OK to close the Current Sequence and Current windows and return to the main window Press the Single tab to see the measurements in numeric and graphical form Set the graph scales by pressing Set Scales This opens the graph scales window Ensure that autoscaling is turned on press Autoscale to toggle autoscaling on off the status of autoscaling is shown by the adjacent indicator Use the radio and up down or ellipses buttons to set the x axis to 60 minutes Y Axis X Axis Channel Scale Minutes ee eee Minimum Time Units 0 Seconds 10 Autoscale 7 E OK Cancel Maximum Minutes Press OK to return to the main window The measurement system will now accumulate data and after 60 minutes the graph will begin to scroll to show the last 60 minutes of data The two boxes to the right of the Set Scales button normally display the mean and standard deviation of the measurements and these statistics can be cleared reset by the adjacent Clear button However when zero power extrapolation is enabled these are replaced by the last calculated zero power value and its associated uncertainty calculated from the standard deviation of each set of measurement data The Clear
114. tings for the microK using the Backup Configuration button in the Instrument tab see section 3 7 11 This is useful if you use the microK in a number of different ways for example at different times you may use it to perform fixed point calibrations on single SPRTs and comparison calibrations of a thermocouple against two SPRTs You can then reload the required configuration see section 3 7 12 rather than having to enter all the settings for that particular measurement configuration individually 3 11 Password Protection of Key Settings All settings and parameters that affect measurements are password protected This helps you to establish working procedures that meet the requirements of accreditation bodies and should alleviated some of the concerns that accreditation bodies have about the integrity of measurements You need to enter the password to perform the following tasks create edit delete a thermometer database entry create edit delete a reference resistors database entry backup internal data to a USB flash drive overwrite a data file on the USB flash drive delete internal data files backup a configuration load a configuration change the password upgrade the software or firmware SS amp amp amp amp SYSE Page 51 of 117 Issue 1 05 4 Connecting Thermometer Sensors 4 1 The Cable Pod Connectors The Eichmann Cable Pod connectors used on the microK have gold plated t
115. tion Type in a name for the connection such as microK and select an icon In the next window select the PC s COM port to which you have connected your microK from the Connect using drop down list and click OK In the next window enter the data format for the microK s RS232 interface GB COM14 Properties po Port Settings Bits per second 9600 x Data bits 8 iv Parity None x Stop bits 1 v Flow control None x Restore Defaults OK Cancel Apply Click OK to open a Hyperterminal session with the microK Now save using FilelSave As the Hyperterminal connection so that in future you only have to click on this icon to open an RS232 connection with your microK SVS Page 90 of 117 Issue 1 05 Type IDN into Hyperterminal terminate the command by pressing the carriage return or Enter keys the microK should then respond with a string in the form Isothermal Technology microK 100 09 P110 firmware version 1 16 This confirms that you have successfully established an RS232 connection with your microK SVS Page 91 of 117 Issue 1 05 Cor Anko g 10 11 12 Shell 10 GPIB Interface The microK is equipped with an IEEE 488 GPIB General Purpose Interface Bus port This can be used to control the microK and perform calibration and diagnostic functions The command set uses the SCPI Standard Commands for Programmable Instruments protocol see section 11 for det
116. tually selected until a measurement is started using either the INITiate or READ commands The channel numbers used for the internal reference resistors are i Channel 203 25 Q l Channel 204 100 Q l Channel 205 400Q Example to select channel 2 as the reference channel for the next resistance measurement use SENS FRES REF 2 11 6 12 Command SENSe FRESistance REFerence Format SENSe FRESistance REFerence SYSE Page 103 of 117 Issue 1 05 Reports the channel selected as the reference channel for the next resistance measurement Example a microK set to use channel 2 as the reference in the next resistance measurement will respond to the command SENS FRES REF with 2 11 6 13 Command SENSe FRESistance RANGe Format SENSe FRESistance RANGe UPPer lt resistance range gt lt current gt Sets the range for the next resistance measurement The range is determined by the voltage range of the measurement system 0 125 or 0 5V and depends on the sense current used The current parameter is the current you intend to use in the measurement this may not be the same as the present value of sense current that is set with the CURRent command The 2 resistance ranges available with the microK are resistance range 0 125V current resistance range 0 5V current The resistance range specified should be the higher of the maximum PRT resistance and reference resistor since the measurement system h
117. und potential In this way both the current source and Amplifier see no significant change in voltage common mode signal between the measurements of the Reference Resistor and the SPRT 7 5 Minimising Thermal EMFs Thermal EMFs EMFs generated as a result of junctions between dissimilar metals at different temperatures are a potential source of error when working at this precision These can largely be eliminated when measuring resistance thermometers by reversing the current and averaging the measurements the offsets in the two measurements cancel each other out when the readings are averaged together However this technique cannot be used when measuring temperature with thermocouples so the thermal EMFs need to be eliminated at source For this reason we used tellurium copper gold plated as the connector SVS Page 75 of 117 Issue 1 05 contact material since this combines good mechanical properties with extremely low thermal EMFs against the copper terminations of a thermocouple In order to eliminate thermal EMFs from the measurement system already small the input connections are reversed immediately behind the input terminals Measurements made with and without the reversal are then averaged together to eliminate the thermal EMFs The limitation is then the thermal EMFs generated by the devices used to implement this reversal 7 6 Solid State Switching One of the most common sources of failure in instruments of
118. urements that rival those of a good electrical metrology laboratory For example for a 25Q SPRT a 0 1mK temperature uncertainty corresponds to 10uQ resistance uncertainty With a ImA sense current this corresponds to a voltage uncertainty of 10nV The microK has been optimised for electromagnetic compatibility minimising emissions and maximising immunity However since the microK is capable of eors Page 57 of 117 Issue 1 05 measuring to such low signal levels it is worthwhile adopting good electrical measurement practices Here are a few guidelines The most sensitive points are the inputs to the microK measuring to better than 10nV Whilst the microK will work satisfactorily with just a four wire connection to the PRT or reference resistor using the voltage sense and current terminals marked V and T respectively it is better to use a screened cable and to connect the screen to the measurement ground terminal above the input terminals Screen Measurement Ground Terminal SPRT or i OS Reference Resistor H A gt The screen should also be connected to the outer sheath of the SPRT if it is metal clad or the case of the reference resistor The use of screened cables is more important when the microK is used with thermistors which have a higher resistance than PRTs or thermocouples Keep the cables to the microK input terminals away from other cables that might be sources o
119. with the extension dat This file can be transferred to a PC and analysed using Excel see section 3 7 9 for details Tip You can perform a comparison calibration on a PRT by connecting it to channel 3 and measuring its resistance and the temperature of the reference SPRT as they are immersed in number of temperature sources fixed point cells liquid baths of block baths Using this data the calibration information for the PRT can be generated Tip In comparison calibrations any error in the value of the reference resistor causes an error in the measured resistance of the PRT to be calibrated but also causes a corresponding error in the temperature measured using the SPRT provided that the same reference resistor is used for both thermometers These correlated errors mean that the measured resistance temperature point corresponds to a valid point further up or down the PRT s resistance versus tempertaure characteristic and therefore does not cause any calibration error provided that the slope of the resistance versus temperature characteristic is the same for the PRT and SPRT Any small difference between the slope of the PRT and SPRT will lead to an error this is calculable and should be included in any uncertainty budget In effect it is only necessary to know the temperature of the SPRT and the ratio of the resistance of the PRT to that of the SPRT on order to transfer the calibration from the SPRT to the PRT It is
120. y a microprocessor connected to the rear panel RS232 interface and a GPIB port The measurement system can be controlled by SCPI commands from either of these The firmware makes no distinction between commands received on the RS232 interface and those from the GPIB and will process these in the order in which they are detected If a response is expected it will always be sent on the interface RS232 or GPIB on which the corresponding command was sent There is no direct interference between measurements made using the front panel operator interface and measurements requested using SCPI commands However measurements take some time to complete so there may be a delay in responses to SCPI commands if measurements are being made via the front panel operator interface To avoid unnecessary delays to responses to SCPI commands you can stop all measurements requested via the front panel operator interface The easiest way to do this is to restart the microK and then not press Resume in the opening window The main application that provides the user interface will then not start and no measurements will be requested 11 6 1 Measuring Resistance using SCPI Commands In order to measure the resistance of a PRT you need to set the microK to measure resistance set the sense current select the measurement range select the measurement channel select the reference channel make the measurement COC S S S amp M If you want to measure a 25
121. y work This uncertainty can be eliminated by determining the resistance of the SPRT at zero current zero power Whilst the resistance cannot be measured with zero current it is possible to measure the resistance at 2 different currents and extrapolate back to determine the value at zero current The most common way to do is this to make a measurement at the normal current and then to increase or decrease the current by a factor of V2 1 414 This changes the power by a factor of 2 and allows easy determination of the zero power resistance by subtracting the change in resistance from the first measurement Although V2 is commonly used since it makes the calculation easy any two currents can be used in the extrapolation process The microK in common with other thermometry bridges supports the ability to vary the sense current in this way in order to support extrapolation back to the zero power resistance It provides xV2 and V2 buttons to simplify the scaling of the current Uniquely the microK is able to sequence the current and generate a zero power corrected value and an uncertainty figure for this value without using any external software Each zero power measurement consists of three sets of readings taken at the normal current the alternate current and then the normal current again The Sors Page 61 of 117 Issue 1 05 number of readings taken at each current can be defined as can the settling time allowed for t
122. ypad window and enter the maximum operating temperature for the thermometer Conversion box This box contains the conversion to temperature used for the selected thermometer If you are creating a new thermometer entry use the up down buttons to select the required conversion Coefficients button This button opens a window that allows you to enter the coefficients required for the temperature conversion In the case of ITS 90 or thermocouples these are the coefficients for the deviation function the base conversion coefficients are fixed Conversion Name Conversion Type ITS90 ITS 90 R 0 01 25 4956321 Coefficients for T lt 0 01 C Coefficients for T gt 0 01 C A Be a 0 0 00029667298 fae b 0 b 2 3806071e 05 e 3 0497121e 06 d 0 A ms wes0 323 0 e eS Page 41 of 117 Issue 1 05 Conversion Name Conversion Type Type AuPt Thermocouple a AuPtThermocouple Ref Function MinT C 0 MaxT C 1000 New button Press this button to make a new thermometer entry into the microK s database Delete button Press this button to delete the selected thermometer or the current entry for a new thermometer from the database OK button Press this button to confirm the changes and close the window 3 7 2 Edit Resistors

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