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1. 4 3 2 2 Smoothing Filter 5 3 2 3 Low Pass Filter 5 3 2 4 Power Line Rejection Filter 5 3 2 5 Interface Status 5 3 3 Setup Screen 5 3 3 1 Selecting the Computer Interface 5 3 3 2 Selecting the RS 232 Baud Rate 6 3 3 3 Setting the Ethernet Parameters 6 3 3 4 Setting the Alarm Limits 7 3 3
2. 19 5 3 1 Choosing a LAN Structure 19 5 3 2 Setting the Public Network Parameters 20 5 3 3 Setting Private Network Parameters 20 5 3 4 Connecting to the Network 20 5 4 Testing the Remote Interface 21 5 4 1 Testing the RS 232 Connection 21 5 4 2 Testing the Ethernet Connection 21 5 5 Command Processing 23 5 5 1 How SCPI Commands are Structured and Executed 23 5 5 2 Sending Multiple Commands in One Command String
3. 35 5 8 5 Clearing the Event and Event Enable Registers 35 6 Theory of Operation 36 6 1 Introduction 36 6 2 Overview 36 6 2 1 Embedded Microprocessor 36 6 2 2 User Interface 36 6 2 3 Analog Data Filtering and Conversion 36 6 3 Fluxgate Magnetometer Theory 38 6 3 1 Sensor Construction 38 6 3 2 Fluxgate Operation
4. 42 APPENDIX A SPECIFICATIONS RM100 User s Manual June 2004 MEDA Inc vi Table of Figures Page Figure 2 1 Front Panel 2 Figure 2 2 Rear Panel 2 Figure 4 1 Vector representations of a magnetic field 13 Figure 5 1 Results of pinging the RM100 22 Figure 5 2 RM100 Status Register Structure 34 Figure 6 1 RM100 Block Diagram 37 Figure 6 2 RM100 Sensor Configuration 38 Figure 6 3 Fluxgate Sensor Operation 39 Figure 6 4 Block Diagram of the Fluxgate Sensor
5. 38 6 3 3 Sensor Signal Processing 40 6 4 Analog Magnetometer Circuit Configuration 40 6 4 1 Excitation Circuit 40 6 4 2 Signal Conditioner 41 6 4 3 Neutralization Circuit 41 6 5 Analog Output Filtering 42 7 Maintenance 42 7 1 Probe Precautions 42 7 2 Fuse Replacement 42 7 3 Calibration Cycle
6. 23 5 5 3 How the Computer Receives Data 24 5 5 4 How the RM100 Indicates Over Range of Invalid Data 24 5 5 5 Commands that are Protected 25 5 6 Command Summary 25 5 7 Error Message Summary 32 5 8 Status Structure 33 RM100 User s Manual MEDA Inc June 2004 v 5 8 1 Status Byte Register 33 5 8 2 Questionable Event Register 33 5 8 3 Standard Event Status Register 35 5 8 4 Operation Event Register
7. 10 3 6 2 Displaying Data Buffer Statistics 10 3 7 Selecting the Units for the Displayed Magnetic Field Measurement 10 3 8 Storing and Plotting Data 10 3 8 1 Storing Data in the Data Buffer 11 3 8 2 Plotting Data Stored in the Data Buffer 11 RM100 User s Manual June 2004 MEDA Inc iv 3 9 Saving and Recalling Data Stored in the Buffer 11 3 9 1 Saving the Data Buffer in Non Volatile Memory 11 3 9 2 Recalling Data Stored in Non Volatile Memory 12 3 10 Retrieving Error Messages 12 4 Applications 12 4 1 Magnetic F
8. 4 4 Using the Null Function to make Accurate Measurements The RM100 can be used as a null detector to achieve greater measurement accuracy This is accomplished by using the offset field to cancel null the field being detected by the sensor When the field detected by the sensor is null the value of the offset field equals the negative of the field that it is being measured The offset field has an accuracy of 0 01 of the setting and is traceable to NIST 4 4 1 Using the Null Function for a single Measurement The Null keypad function accomplishes this task automatically When the Null key is pressed the following actions take place 1 The range is set to 100 T and smoothing is turned off 2 The offset field is set to zero 3 The ambient field is measured and then the offset field is set to minus the ambient field RM100 User s Manual June 2004 MEDA Inc 16 4 The range is changed to 1 T 5 The difference between the ambient field and the offset field is measured 6 The offset field is trimmed based on the difference field measurement 7 The range is changed to 0 1 T and steps 5 and 6 are repeated This whole process takes about 3 seconds Unless the field is changing rapidly the null field should now be under 1 nT The actual field can be determined using the following equation Actual field offset field difference field The difference field accuracy is 1 of the reading 1 nT ther
9. Highlight the MASK field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new Mask address in dot decimal notation e g 255 255 255 0 If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value To set the GATE address Highlight the GATE field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new gateway router address in dot decimal notation e g 192 168 0 1 If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value To set the PORT value Highlight the PORT field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new port value the default port is 20001 The port value must be between 0 and 65536 If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value RM100 User s Manual MEDA Inc June 2004 7 3 3 4 Setting the Alarm Limits The operator can set minimum and maximum alarm limits from 99999 nT to 99999 nT The maximum alarm limit must
10. R E G I S T E R S Polarity State Off On Analog Out Data 18 bits Corner Frequency 4 bits Range 4 bits 256 x 64 Dot Vacuum Fluorescent Graphics Display 4 x 4 Membrane Keypad RCM2200 Microprocessor 512K Flash 512K RAM 8 bits Select 4 8 bit Registers 8 bits RX TX Column 4 bits Row 4 bits Power Regulation and Distribution Circuit 5 VDC 5 VDC 15 VDC 15 VDC RM100 Electronic Unit RM100 Sensor Unit Analog Output RS 232 Interface 7 5 VDC Power Input RJ45 Ethernet Interface Figure 6 1 RM100 Block Diagram RM100 User s Manual June 2004 MEDA Inc 38 6 3 Fluxgate Magnetometer Theory This section provides a brief description of how fluxgate sensors convert magnetic field into a usable voltage that represents the magnitude and direction of the magnetic field vector 6 3 1 Sensor Construction The basic fluxgate sensor configuration is illustrated in Fig 6 2 Figure 6 2 RM100 Sensor Configuration The RM100 uses the Schonstedt fluxgate sensor configuration that consists of a hollow ceramic tube around which is wound two interwoven pieces of thin Permalloy tape The excitation winding is wound in a toroidal fashion through the center and around the outside of the ceramic tube The signal winding is a solenoid centered on the ceramic tube The neutralization winding not shown is a solenoid wound on a temperature stable tub
11. RM100 NANOTESLA METER User s Manual December 2004 MEDA Inc Macintyre Electronic Design Associates Inc 22611 Markey Court Suite 114 Dulles VA 20166 RM100 User s Manual June 2004 MEDA Inc ii Warranty This instrument is warranted by Macintyre Electronic Design Associates Inc MEDA to be free from defects in materials and workmanship If a defect is discovered within one 1 year from date of purchase MEDA will service the instrument as long as the original purchaser returns it to our factory The original purchaser must prepay all transportation charges and demonstrate that the defect is covered by this warranty Model and serial number must be supplied for service If the cause of the instrument failure is found to be misuse or abnormal operating conditions repairs will be billed at cost upon authorization from the customer Under no circumstances will MEDA s liability exceed the cost to repair or replace the defective parts MEDA s liability will cease and terminate at the completion of the one year warranty period RM100 User s Manual MEDA Inc June 2004 iii Table of Contents Page 1 Introduction 1 2 Getting Started 1 2 1 Unpac
12. 16 4 5 2 Checking the Residual Field in a Magnetic Shield 17 4 6 Calibrating Helmholtz Coils and Solenoids 17 5 Computer Interface Operation 18 5 1 Introduction 18 5 1 1 Local and Remote Operation 18 5 1 2 Computer Interfaces 18 5 1 3 Single Client Operation 18 5 2 Preparing for RS 232 Operation 19 5 2 1 Setting the Communications Parameters 19 5 2 2 Connecting to a Computer 19 5 3 Preparing for Ethernet Operation
13. 28 Command Parameters Description SAMPle SAVE Equivalent to pressing the Save key Transfers the measurements stored in the data buffer to non volatile memory SENSe NULL STATe ON OFF AUTO Equivalent to pressing the Null key ON to initiate the Null function or the Shift Null key OFF to clear the offset field or Shift Offset key AUTO to initiate the Auto Null function SENSe NULL STATe Returns the null state OFF ON or AUTO SENSe NULL VALUe lt value gt MIN MAX Sets the value of the offset field to lt value gt which can range from 99999 to 99999 nT SENSe NULL VALUe Returns the current value of the offset field in nT SENSe RANGe lt value gt MIN MAX Sets the range of the displayed difference field and the analog output lt value gt represents the maximum expected signal level in uT and must be between 0 1 and 100 The RM100 selects the appropriate range for the requested value MIN 0 1 T MAX 100 T SENSe RANGe Returns the current range of the difference field display and the analog output SENSe SMOothing POINts lt value gt Sets the number of points in the smoothing filter running average lt value gt must be between 1 and 100 The RM100 selects 1 3 10 50 or 100 points based on lt value gt SENSe SMOothing POINts Returns the number of points being used by the smoothing filter running average SENSe
14. Earth s field magnitude R 1 Place the RM100 in the 100 T range 2 Rotate the sensor in the horizontal plane for a maximum field reading 3 Rotate the sensor vertically for a new maximum 4 Secure the sensor and press the Null key The RM100 will generate an offset field that nulls the field at the sensor and the display will show the difference between the offset field and the Earth s magnetic field 5 Rotate the sensor slightly until the difference field peaks then secure the sensor again 6 Press the Null key one more time 7 Record the value ignoring the sign shown in the Offset field This value is the magnitude of the Earth s magnetic field vector in nT The accuracy of the measurement using this technique is 0 01 of the value 4 3 3 Monitoring the Earth s Field Magnitude The Earth s field can change several hundred nT during a 24 hour period Use the Auto Null function to achieve the greatest measurement accuracy when monitoring the Earth s field magnitude Use the procedure described in section 4 3 2 to align the sensor with the Earth s field vector then activate the Auto Null function by pressing the Shift key followed by the Offset key The displayed field value equals the Earth s magnetic field magnitude As the Earth s field changes the Auto Null function will continuously update the nulling offset field so that the displayed value maintains an accuracy of 0 01 of the reading 0 2 nT
15. 0 OFF 1 ON The Limit function is disabled when the RM100 is in the Auto Null mode CALCulate LIMit FAIL Returns the result of the limit test 0 Pass 1 Fail CALCulate LIMit CLEar Clears the fail indicator FETch Returns the contents of the data buffer The measurements returned are delimited by commas and are in the current units Use SENS UNIT To retrieve the unit value INITiate Equivalent to pressing the Store key This starts the storage of measurements into the data buffer No new commands will be processed until the data buffer is full NULL ON OFF AUTO Equivalent to pressing the Null key ON to initiate the Null function or the Shift Null key OFF to clear the offset field or Shift Offset key AUTO to initiate the Auto Null function NULL Returns the null state OFF ON or AUTO OUTPut LPFilter lt value gt MIN MAX Sets the analog output low pass filter corner frequency lt value gt must be between 0 and 1000 The RM100 selects one of the available corners that best meets the requested corner The fixed corner frequencies are 10 50 100 500 and 1000 Hx RM100 User s Manual MEDA Inc June 2004 27 Command Parameters Description MIN 10 Hz MAX 1000 Hz OUTPut LPFilter Returns the current low pass filter corner frequency in Hz OUTPut PLReject in out Sets the analog output notch filter in or out When the notch filter is in 60 Hz sig
16. 5 Setting the Maximum Data Buffer Size 7 3 4 Offset Field Operations 7 3 4 1 Using the Null Function to Measure the Ambient Field 8 3 4 2 Using the Auto Null Function to achieve Maximum Measurement Accuracy 8 3 4 3 Manually Entering the Offset Field 8 3 4 4 Clearing the Offset Field Value 8 3 4 5 Measuring Small Changes in the Ambient Field 9 3 4 6 Calibrating the Analog Output Scale Factors 9 3 5 Enabling Disabling the Limit Alarm Function 10 3 6 Generating and Displaying Statistics 10 3 6 1 Continuously Computing Measurement Statistics
17. Basic Settings When the RM100 is turned ON after the self test finishes its settings default to the following Range RNG 100 T Units T Smoothing SMO 1 point no running average Low Pass Filter LPF 10 Hz corner frequency Power Line Rejection Filter PLR out Interface IF local The following subsections describe how the operator using the front panel keypad can change these settings To change any of these settings press the Settings key on the keypad This will cause the RNG field to be highlighted Use the up and down arrows to select a different setting Use the left and right arrows to move to another field to change Press the Escape key to return to normal operations 3 2 1 Range The RM100 has four difference field range settings 100 10 1 and 0 1 T Use the up and down arrows to cycle through the selections The difference field equals the ambient field minus the offset field The difference field value is displayed on the VFD as well as output as an analog signal through a dual banana plug connector on the rear panel RM100 User s Manual MEDA Inc June 2004 5 3 2 2 Smoothing Filter After pressing the Settings key press the right arrow until the SMO field is highlighted The RM100 has five smoothing filter setting 1 3 10 50 and 100 The smoothing filter is a running average with a length determined by this setting A setting of 1 turns averaging OFF A
18. OK key This will erase the current value and place a cursor at the beginning of the field Type in the new maximum data buffer size If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value 3 4 Offset Field Operations The RM100 sensor is surrounded by a solenoid that is used to generate an offset field The RM100 sensor measures the difference between the ambient field at the sensor and the offset field produced by the solenoid The offset field is very accurate and its accuracy is traceable to NIST The offset field function can be used to Accurately measure a static magnetic field Null neutralize the ambient field so that small changes in the field can be measured accurately Calibrate the analog output scale factors RM100 User s Manual June 2004 MEDA Inc 8 Measure fields up to 200 T 3 4 1 Using the Null Function to Measure the Ambient Field The ambient field component along the sensitive axis of the sensor can be measured accurately by pressing the Null key The RM100 will automatically apply an offset field that will null the ambient field The value of the nulling neutralizing field which is displayed in the Offset field in the middle of the screen is the negative of the value of the ambient field The value of the offset field has an accuracy of 0 01 of the re
19. String Multiple commands can be included in the command string The SCPI language uses a semicolon to separate the commands An example follows SENS NULL STAT ON SENS NULL VALUE READ This command string includes three commands separated by semicolons The first command causes the RM100 to null the ambient field The second command request that the value of the offset nulling field be returned to the computer The third command requested that the value of the difference field ambient field offset field be returned to the computer RM100 User s Manual June 2004 MEDA Inc 24 If an error occurs in executing the command the ERROR annunciator will turned on The commands up to the point of an error are executed Commands following an error are not executed There are many possible sources of errors The most common ones are syntax errors missing parameters and parameter values that are out of bounds Use the SYST ERR Command to retrieve error messages In a command string that contains multiple commands if the next command in the string is on the same level as the last substring the upper level portion of the path does not need to be included The above command could have been entered as follows SENS NULL STATE ON VALUE READ Since STATE and VALUE have the SENS NULL path in common there is no need to repeat this path information in front of the VALUE command The READ command needs a colon in front of it since it
20. The RM100 is a replacement for the obsolete Schonstedt Instrument Company HSM 2 Reference Magnetometer that has been the standard instrument used for high accuracy magnetic field measurements over the last thirty years The RM100 maintains the same accuracy but with the enhanced capabilities afforded by current microprocessor and analog to digital converter technology Some of the features of the RM100 are 0 1 nT resolution 0 01 basic accuracy traceable to NIST 0 5 ppm C stability of the offset field 200 T measurement range One button ambient field cancellation and measurement 100 10 1 and 0 1 T analog output ranges for recording and other purposes Measurement statistics such as minimum maximum and average values Data storage and on screen plotting up to 16 384 samples Remote programming and data acquisition using either RS 232 or Ethernet connections SCPI Version 1999 0 compliant remote programming National Instruments LabView drivers An alarm capability for alerting the user of signals that exceed user set limits The RM100 can be used to Screen for magnetic contamination Monitor Geomagnetic field variations Measure rock magnetism Calibrate Helmholtz coils and solenoids used to generate precision fields Check shielding effectiveness Measure the dipole moments of equipment Detect satellite stray f
21. They can also be downloaded from their web site http www scpiconsortium org 5 5 1 How SCPI Commands are Structured and Executed The SCPI language uses a tree structure similar to the file structure used in computer operating systems There is a set of top level or root commands Beneath each root level command there are associated sublevel commands and so on The complete path root gt subroot gt subsubroot etc must be specified before it can be executed An example command is shown below SENSor NULL STATe ON lt CR gt The capital letters are required The lower case letters are optional The command string is case insensitive You can use either the abbreviated or the full command name but nothing else otherwise you will generate an 113 Undefined header error In this example SENSor is the root command NULL is a subcommand of SENSor and STATe is a subcommand of NULL ON is a parameter of the STATe subcommand The lt CR gt at the end of the line indicates to the RM100 that the command is complete and to process it This command sets the state of the null condition of the RM100 to ON This causes the RM100 to null the ambient field in the same way as if the user had pressed the Null key on the front panel The colon in the front of the first command indicates that it is a root command If the root command is the first command in the string the colon is not needed 5 5 2 Sending Multiple Commands in One Command
22. alarm is initially disabled Press the Alarm key to enable the alarm The Al annunciator will be displayed when the alarm is enabled Press the Alarm key again to disable the alarm When the alarm is enabled the alarm will sound and remain active whenever the difference field is outside the specified limits The difference field equals the ambient field minus the offset field Before activating the alarm use the Null function to cancel the ambient field The limit alarm function is disabled if the RM100 is in the Auto Null mode 3 6 Generating and Displaying Statistics Measurement statistics can be computed continuously while measurements are being made or just on the data in the data buffer 3 6 1 Continuously Computing Measurement Statistics The RM100 can compute the measurement statistics on an unlimited number of data points Only the statistics are retained not the actual measurements upon which the statistics are based Press the Stats key to start continuous computation of measurement statistics The Stats annunciator is displayed the statistics variables are initialized and statistics on all future measurements begins Pressing the Stats key a second time stops the collection of measurement statistics turns off the Stats annunciator and clears all statistics variable Press the Shift key followed by the Stats key to display the current values of the measurement statistics These values will be displayed in the upper right corner of
23. an over range OVR condition will be 9 9E37 An over range condition can also generate invalid statistical data When a statistical value has invalid data associated with it the RM100 will return 9 9E37 which indicates the value is not a number NAN Commands that can return this value include READ FET CALC AVER AVER CALC AVER MIN CALC AVER MAX CALC AVER PTP SAMP AVER SAMP MIN SAMP MAX and SAMP PTP RM100 User s Manual MEDA Inc June 2004 25 5 5 5 Commands that are Protected Certain commands are protected when the RM100 is collecting statistics or storing data in order to prevent the state of the RM100 from changing thereby corrupting the data These protected commands will generate a 203 Command protected error The commands that are protected include NULL SENS RANG SENS SMO SENS NULL STAT and SENS NULL VALUE 5 6 Command Summary Table 5 3 is a summary of all of the RM100 remote commands The commands that start with are called common commands that are common to all instruments that implement the SCPI command structure The root commands are shown in red Table 5 3 Summary of remote RM100 commands Command Parameters Description CALCulate AVERage AVERage The Stats function must be active see CALC AVER STAT Returns the average value of the field since the Stats function was activated CALCulate AVERage COUNt The Stats function must be active see CALC AVER STAT
24. and the serial port parameters are identical to the RM100 settings 1 Select Call gt Disconnect from the Hyper Terminal menu to disconnect from the RS 232 interface 2 Select File gt Properties gt Configure from the Hyper Terminal menu and verify that the communication parameters agree with the RM100 settings 3 Click OK and select the Settings tab on the top of the dialog box 4 Click on the ASCII Setup button 5 Check the Send end lines with line feed and Echo typed characters locally boxes 6 Click OK twice to return to the main screen 7 Select Call from the Hyper Terminal Call main menu and then click on Call to connect to the RM100 8 Send the following command SYST REM lt CR gt The lt CR gt represents a carriage return which is generated by pressing the Return key 9 Hyper Terminal should echo the command The IF field on the front panel of the RM100 should change from loc to rem 10 Send the following command IDN lt CR gt 11 The RM100 should respond with MEDA RM100 nnnnnn n n nnnnnn is the RM100 s serial number n n is the firmware version The ERROR annunciator will be turned on if an error occurred Use the SYST ERR command to retrieve the error message describing the cause of the error section 3 10 explains how to retrieve error messages from the front panel 5 4 2 Testing the Ethernet Connection The RM100 must be reachable from the network to which the host computer is connect
25. business today where host PCs and other network enabled equipment are connected together and to the Internet through switches hubs and routers RM100 User s Manual June 2004 MEDA Inc 20 A private network is defined as a network consisting of host PCs and other network enabled equipment that is not connected to the public network or to the Internet A private network can define its own IP addresses and other communication parameters without having them assigned by an internationally recognized authority 5 3 2 Setting the Public Network Parameters The RM100 uses a static IP address to communicate over a network using the TCP IP protocol Before connecting the RM100 to the public network the user must obtain the following static IP parameters from the network administrator Host IP address Network mask Gateway router IP address Once this information is gathered refer to section 3 2 3 for a description of how to enter this information into the RM100 5 3 3 Setting Private Network Parameters The Internet Corporation for Assigned Names and Numbers ICANN assigned a set of numbers that can be used for private networks If a device with one of these IP addresses is connected to the Internet it will not cause a disruption since routers automatically filter out these addresses The following addresses are designated for private networks 10 0 0 0 through 10 255 255 255 a single Class A network
26. field measurements The field measurements have an accuracy of 0 01 of the reading 1 nT DC current can be measured to an accuracy of better than 0 001 so it is possible to measure the coil constant to the same accuracy as the field measurements 5 Computer Interface Operation 5 1 Introduction The RM100 can be controlled remotely through two different physical interfaces The commands are independent of the physical connection This section describes how to connect and use these interfaces to send commands to the RM100 5 1 1 Local and Remote Operation The RM100 has two operating modes local and remote The operating mode is displayed in the IF field on the bottom line of the display In the local mode all keypad functions are available to the user In the remote mode only the Local key function is available Pressing the Local key when the RM100 is in the remote mode will return it to the local mode In the local or remote mode the RM100 will respond to commands received through the computer interface Place the sensor in the remote mode using the SYST REM command to prevent use of the keypad except for the Local key during remote operation 5 1 2 Computer Interfaces The RM100 has two computer interfaces RS 232 and Ethernet Only one of these interfaces can be active at any one time The active interface is defined in the Setup screen see section 3 2 1 Both interfaces use the same command set The RS 232 serial con
27. input of the Phase Detector Integrator The Phase Detector synchronously switches the AC amplifier output between the two inputs of the Integrator at twice the excitation frequency This has the effect of converting the 14 kHz signal into a DC voltage at the output of the Integrator The magnitude of the DC signal is proportional to the amplitude of the sensor signal and its polarity is positive if the sensor signal is in phase with the reference signal or negative if it is 180 degrees out of phase with the reference signal The DC voltage at the output of the phase detector is amplified and fed to the positive input of the Range Amplifier The output of the Range Amplifier is feed back to its negative input forcing the negative input of the Range Amplifier to equal the output voltage of the DC Amplifier This voltage is connected through Rf to the sensor signal winding The resulting current through the sensor signal winding produces a magnetic field in the sensor that counters the magnetic field being measured The 100 10 and 1 T ranges are set by switching in different values of resistance between the output of the Range Amplifier and its negative input The amplifier following the Range Amplifier provides a gain of 2 for the first three ranges and a gain of 20 for the 100 nT 6 4 3 Neutralization Circuit The neutralization circuit produces a very accurate and precise magnetic field to the sensor A temperature stable solenoid surrounding the
28. is a root command and is not in the same branch as the SENS commands White space spaces and tabs are allowed anywhere within the command string A white space is required between a command and its associated parameters such as ON in the above example Commands that have a at the end return information to the computer 5 5 3 How the Computer Receives Data Some commands such as READ return data When a command returns data the data is followed by a lt CR gt lt LF gt combination For example the READ command would return 42192 lt CR gt lt LF gt where 42192 is the value of the field Some commands return multiple values The FETCH command is an example Each returned measurement point is separated by a comma The last measurement point is followed by a lt CR gt lt LF gt combination This is illustrated in the following example Command gt FET lt CR gt lt LF gt Response gt 14365 2 14366 0 14370 3 14371 5 14360 4 lt CR gt lt LF gt In this example five 5 measurement points were returned Another example is the SYS DATE command Command gt SYST DATE Response gt 2004 7 22 lt CR gt lt LF gt In this example 2004 is the year 7 is the month and 22 is the day White space may precede each value in the returned string between the comma and the first significant digit 5 5 4 How the RM100 Indicates Over Range of Invalid Data The data returned to the computer when the RM100 is in
29. sensor produces the field in response to currents generated by a very accurate and stable voltage to current converter The voltage to current converter utilizes a very linear and stable unipolar 18 bit analog to digital converter DAC and a low temperature coefficient TC sensor resistor to achieve this accuracy The two pole double RM100 User s Manual June 2004 MEDA Inc 42 throw switch controls the polarity of the field and the single pole double throw switch turns the field off or on 6 5 Analog Output Filtering The RM100 provides a filtered analog output that can be used to record magnetic field data The output of the analog magnetometer connects to the input of the power line rejection filter and one position of a single pole double throw switch The power line rejection filter output connects to the other position of the switch The pole of the switch connects to the input of a programmable 4 pole Butterworth low pass filter The output of the low pass filter goes to a connector on the back panel of the RM100 The low pass filter provides 24 dB per octave attenuation of frequencies beyond the 3 dB point This filter essentially eliminates any ripple signals at the sensor excitation frequency and its harmonics When connected in the filter chain the power line rejection or notch filter provides at least 40 dB of attenuation of magnetic fields produced by power line current flow The attenuation is at the fundamental frequenc
30. setting of 3 will continuously average the most recent 3 data values 1second and display the result on the front panel A setting of 10 will continuously average the most recent 10 data values 3 333 seconds and display the results on the front panel etc The smoothing filter is used to provide higher resolution measurements of static magnetic fields It is an ideal feature for calibrating precision magnetic field sources such as Helmholtz coils and solenoids but it can also be used to measure slow variations in the geomagnetic field 3 2 3 Low Pass Filter After pressing the Settings key press the right arrow until the LPF field is highlighted The RM100 has five filter settings 10 50 100 500 and 1000 Hz The low pass filter is a four pole Butterworth with a 24 dB octave roll off beyond the corner frequency The LPF filters the difference field analog signal going to the analog output connector on the rear panel 3 2 4 Power Line Rejection Filter After pressing the Settings key press the right arrow until the PLR field is highlighted The RM100 power line filter can be set to in or out The power line rejection filter provides a minimum 40 dB notch at the power line frequency of 60 Hz 50 Hz optional The PLR filters the difference field analog signal going to the analog output connector on the rear panel 3 2 5 Interface Status The far right IF field is used to indicate the remote interface status of the RM100 If the RM100
31. the screen Repeat these keystrokes to remove the measurement statistics from the screen The measurement statistics can only be displayed while the Stats annunciator is displayed 3 6 2 Displaying Data Buffer Statistics Measurement statistics on the data in the data buffer can be displayed whenever the Stats annunciator is off Press the Shift key followed by the Stats key to display the data buffer measurement statistics These values will be displayed in the upper right corner of the screen Repeat these keystrokes to remove the data buffer measurement statistics from the screen Data storage is suspended while the statistics are being computed and displayed It is best to wait until the data buffer is full before displaying the measurement statistics 3 7 Selecting the Units for the Displayed Magnetic Field Measurement The user can select the units to be used when displaying the magnetic field measurements The default unit is T To change the units of the displayed magnetic field measurement press the Units key until the desired unit is displayed The choices are T nT or mG 3 8 Storing and Plotting Data The RM100 contains an internal data buffer that can be used to store up to 16 384 data points The default value of the data buffer size is 1024 data points see section 3 3 5 to learn how to change RM100 User s Manual MEDA Inc June 2004 11 the data buffer size The data stored in the buffer can be plotted on the scr
32. to 99 999 9 nT To manually enter an offset field Press the Offset key The polarity position of the Offset field will be highlighted Use the up and down arrows to change the polarity of the offset field or to turn the field OFF blank polarity position Use the left and right arrows to move the cursor to one of the numerical fields Use the up and down arrows to change the value of the numerical field Press the Escape key to exit the offset value entry and return to normal operations The offset field minimum step size is 0 381 nT When entering values in the 0 1 nT field the actual offset field will change only for 0 4 and 0 8 nT entries The Offset keys are inhibited when the RM100 is in the Auto Null mode 3 4 4 Clearing the Offset Field Value The offset field can be cleared set to zero value and turned OFF by pressing the Shift key followed by the Null key This will change the RM100 to the 100 T range and the difference field displayed on the screen will be the current value of the ambient field RM100 User s Manual MEDA Inc June 2004 9 3 4 5 Measuring Small Changes in the Ambient Field Use the Null function to accurately measure small changes in the ambient field The analog output or the Store function can be used to record the changes To measure small changes in the ambient field Press the Null key to null the ambient field Record the value of the offset field w
33. 172 16 0 0 through 172 31 255 255 16 contiguous Class B networks 192 168 0 0 through 192 168 255 255 256 contiguous Class C networks Table 5 2 below lists the factory settings of the RM100 Ethernet communication parameters These are private network addresses and can be safely used for testing purposes or for a dedicated private network Table 5 2 Factory settings for Ethernet interface Parameter Factory Settings Host IP Address 192 168 0 2 Network Mask 255 255 255 0 Gateway 192 168 0 1 Port 20001 5 3 4 Connecting to the Network Connect the RM100 to the network using CAT5 cable with RJ45 connectors Once the RM100 is connected to the network it can be controlled by a host computer using the commands described in section 5 5 2 RM100 User s Manual MEDA Inc June 2004 21 5 4 Testing the Remote Interface After connecting the RM100 to the RS 232 or Ethernet interface test the connection to see if it is operating properly From the host computer run a terminal simulation program that can communicate with the specific interface being tested For Microsoft Windows operating systems the program Hyper Terminal which comes with the operating system can be used to test both the RS 232 and the Ethernet connections The following test procedures assume the terminal simulator is Hyper Terminal 5 4 1 Testing the RS 232 Connection The following procedure assumes that a Hyper Terminal session has been initiated
34. 4 1lists the approximate values of I H Z R and magnetic declination for several U S cities This data was determined by using a computer model available from the U S Department of Commerce The magnetic declination is the angular deviation of the magnetic North with the geodetic North If the sign is positive then the geodetic North is west of the Magnetic north If it is negative then it is east of the Magnetic north Table 4 1Earth s magnetic field components at various US cities City H nT Z nT R nT I deg Declination deg Washington D C 20 535 49 866 53 929 67 13 New York NY 19 508 51 553 55 121 69 13 Miami FL 25 721 39 768 47 360 57 3 Chicago IL 18 643 53 922 57 054 71 1 Denver CO 21 509 50 636 55 015 67 11 San Francisco CA 20 609 49 755 53 854 67 5 19 Los Angeles CA 25 283 42 260 49 246 59 14 San Diego CA 25 674 41 413 48 726 58 14 RM100 User s Manual MEDA Inc June 2004 15 Seattle WA 19 208 52 742 56 131 70 20 New Orleans LA 24 797 43 902 50 421 61 2 Boston MA 18 881 52 003 55 324 70 16 4 3 2 Accurately Measuring the Magnitude of the Earth s Field Vector The above procedure measures the components of the Earth s field vector but the computed magnitude will have errors based on how accurately you aligned the sensor along the three directions Use the following procedure to make a much more accurate measurement of the
35. C Power line reject filter frequency 60 Hz 1 2 Hz maximum 100ppm C Power line rejection filter attenuation 60 Hz 40 dB minimum 1 Full scale range full scale voltage output is 10 Volts General Specifications Digital Smoothing Type Running average Points per average 1 3 10 50 100 Sample rate 3 samples per second 20 power line cycles 60 Hz RS232 serial interface Connector 9 pin D female Baud rates 9600 19200 38400 57600 115200 Ethernet Connector RJ45 Type 10 base T Remote programming language SCPI IEEE 488 2 Version 1999 0 Supply voltage 100 240 VAC 50 60 Hz 1 5A max Display 256x64 dot graphics Vacuum Florescent Controls 16 key membrane keypad Operating environment 0 C to 50 C 10 to 80 R H Electronics unit Dimensions 264 mm x 257 5 mm x 103 mm Weight 2 5 kg 5 5 lbs Sensor Type Single axis fluxgate Dimensions 89mm x 33mm x 24mm Weight 937 g Cable length 50 feet Specifications are subject to change without notice
36. RM100 User s Manual June 2004 MEDA Inc 32 5 7 Error Message Summary Table 5 4 below lists all of the possible error numbers and associated messages Table 5 4 Error numbers and messages Error Number Error Message 101 Invalid character 102 Syntax error 103 Invalid separator 104 Data type error 109 Missing parameter 112 Program mnemonic too long 113 Undefined header 151 Invalid string data 158 String not allowed 203 Command protected 222 Data out of range 224 Illegal parameter value 230 Data corrupt or stale 350 Queue overflow 365 Time out error 522 Output buffer overflow 523 No stored data 524 ADC failure 525 Analog magnetometer failure 526 Neutralizing circuit failure 527 100 T range out of tolerance 528 10 T range out of tolerance 529 1 T range out of tolerance 530 0 1 T range out of tolerance 531 LPF output failed 532 PLR output failed RM100 User s Manual MEDA Inc June 2004 33 5 8 Status Structure The RM100 conforms to the SCPI status register structure There are three event registers with associated event enable registers that feed a Status Byte register that summarizes the status of the RM100 This structure is illustrated in Fig 5 2 5 8 1 Status Byte Register The bits in the Status Byte Register SBR indicate the state of the event registers the Output Queue and the Error Queue The SRQ bit
37. Returns the number of points that have been used in computing the statistics CALCulate AVERage MAXimum The Stats function must be active see CALC AVER STAT Returns the maximum value of the field since the Stats function was activated CALCulate AVERage MINimum The Stats function must be active see CALC AVER STAT Returns the minimum value of the field since the Stats function was activated CALCulate AVERage PTPeak The Stats function must be active see CALC AVER STAT Returns the peak to peak value of the field since the Stats function was activated CALCulate AVERage STATe OFF ON Equivalent to pressing the Stats key Activates or deactivates the Stats function If the Stats function is inactive the CALC functions will return ERR CALCulate AVERage STATe Returns the state of the Stats function 0 OFF 1 ON CALCulate LIMit UPPer lt value gt Sets the upper limit for the limit test lt value gt can range from 99999 to 99999 nT CALCulate LIMit Returns the upper limit value in nT RM100 User s Manual June 2004 MEDA Inc 26 Command Parameters Description UPPer CALCulate LIMit LOWer lt value gt Sets the lower limit for the limit test lt value gt can range from 99999 to 99999 nT CALCulate LIMit LOWer Returns the lower limit value in nT CALCulate LIMit STATe ON OFF Enables disables the limit test
38. Settings key and use the up or down arrows to select the analog output range to calibrate Press the Offset key to highlight the polarity position of the Offset field The polarity position should be blank and the value of the offset field should be zero Use the right arrow to move to the digit position representing the full scale field for the selected range e g if the range is 0 1 T then go to the 100 nT position Use the up or down arrow to set the offset field value to the full scale value of the range being calibrated Use the left arrow to return to the polarity position Press the up arrow to change the polarity of the offset field to and record the analog output voltage Press the up arrow again to change the polarity of the offset field to and record the analog output voltage Compute the scale factor using the following equation nT volts H R R SF 2 where R is the analog output voltage recorded for the positive offset field R is the RM100 User s Manual June 2004 MEDA Inc 10 analog output voltage recorded for the negative offset field and H is the value of the offset field When calibrate the 100 T range use a 99 999 nT offset field since there is no 100 000 nT offset field position 3 5 Enabling Disabling the Limit Alarm Function The limit alarm function limits are set using the Setup screen see section 3 3 4 The
39. Signal Processor 40 Figure 6 5 Block Diagram of the Analog Magnetometer Circuit 41 Table of Tables Page Table 4 1Earth s magnetic field components at various US cities 14 Table 5 1 RS 232 Communication Parameter Factory Settings 19 Table 5 2 Factory settings for Ethernet interface 20 Table 5 3 Summary of remote RM100 commands 25 Table 5 4 Error numbers and messages 32 RM100 User s Manual MEDA Inc June 2004 vii Intentionally left blank RM100 User s Manual MEDA Inc June 2004 1 1 Introduction The RM100 Nanotesla Meter is a high resolution high accuracy single axis fluxgate magnetometer that can be used to measure static magnetic fields over a range of 200 T with a resolution of 0 1 nT Measurement accuracies of 0 01 can be achieved over a range of 100 T using the neutralizing feature of the RM100
40. UNITs uT nT mG Sets the units of the displayed difference field SENSe UNITs Returns the current units of the displayed difference field SENSe TEMPerature Returns the internal temperature of the electronics unit in degrees C Resolution is 0 1 degrees RM100 User s Manual MEDA Inc June 2004 29 Command Parameters Description STATus OPERation EVENT Returns the Operation Event Register value STATus OPERation CONDition Returns the Operation Condition Register value STATus OPERation ENABle lt value gt Places lt value gt into the Operation Event Enable Register which must be an integer between 0 and 32767 STATus OPERation ENABle Returns the Operation Event Enable Register value STATus QUEStionable EVENT Returns the Questionable Event Register value STATus QUEStionable CONDition Returns the Questionable Condition Register value STATus QUEStionable ENABle lt value gt Places lt value gt into the Questionable Event Enable Register which must be an integer between 0 and 32767 STATus PRESet Clears the Operation and Questionable Event Enable registers SYSTem DATE lt year gt lt month gt lt day gt Sets the internal RM100 real time clock to the specified year month and day SYSTem DATE Returns the RM100 real time clock year month and day comma delimited SYSTem ERRor NEXT Return
41. ading 0 2 nT The offset field has a minimum step size of 0 38 nT The main measurement field displays the difference between the ambient field and the neutralizing field and the RM100 is set to the 0 1 T range 3 4 2 Using the Auto Null Function to achieve Maximum Measurement Accuracy The ambient field component along the sensitive axis of the sensor can be measured continuously at the highest accuracy by using the Auto Null feature This function is activated by pressing the Shift key followed by the Offset key In the Auto Null mode the RM100 continuously updates the offset field whenever the ambient field changes by more than 1 1 nT and the magnetic field value offset field difference field is displayed instead of the difference field This mode of operation provides the highest measurement accuracy The Limit Alarm function is disabled when the RM100 is in the Auto Null mode Also the analog output is not usable in this mode since it is continuously zeroed In the Auto Null mode the RM100 can accommodate changes up to a rate of 300 nT per second If the field should change by 100 nT the RM100 will automatically perform the Null function as if the Null key had been pressed The Auto Null function is only effective for fields up to 100 T To measure fields greater than 100 T use the standard Null function 3 4 3 Manually Entering the Offset Field The user can manually enter an offset field of any value from 99 999 9 nT
42. be greater than the minimum alarm limit When the alarm is armed the current measurement is compared to these limits and the alarm is activated while the current measurement remains outside of these limits The default MIN and MAX limits are 5 nT and 5 nT respectively To set the minimum alarm limit Highlight the MIN field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new minimum alarm limit If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value To set the maximum alarm limit Highlight the MAX field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new maximum alarm limit If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value 3 3 5 Setting the Maximum Data Buffer Size The maximum data buffer size determines how much data can be stored using the Store function The default value is 1024 points This represents 341 seconds of data at 3 samples per second The maximum buffer size can be increased to 16 384 points 91 minutes or reduced to 1 point To set the maximum data buffer size Highlight the SIZE field Press the
43. d the measurements made using this technique 4 5 Using the Alarm function There are many situations in which the user would like to see if an object has ferromagnetic properties that produce a magnetic field that exceeds some specified set of limits A Government agency may set magnetic field requirements for all packages shipped by air A spacecraft manufacturer may have a specification for the magnetic field properties of components installed on the spacecraft or for stray fields produced by the spacecraft A magnetic shield manufacturer may have a specification for the residual field within the shield An MRI machine manufacturer may require that the room in which the MRI machine is installed must have an ambient field below some magnetic field limit The RM100 Alarm function is a convenient way to check such requirements without the user constantly having to view the readings on the display 4 5 1 Screening Material for Magnetic Contamination To screen material for magnetic contamination 1 Secure the RM100 sensor to a stable non ferromagnetic surface 2 Set the alarm limits in the Setup screen see section 3 2 4 RM100 User s Manual MEDA Inc June 2004 17 3 Remove all ferromagnetic material from the vicinity of the sensor and from the person who will be handling the material 4 Use the Null keypad function to null the ambient field 5 Press the Alarm key to activate the Alarm function The Al annunciator will be disp
44. depends on the state of the SRB and the Service Request Enable SRE register The SRQ bit is controlled by the SRE register The SBR bits are logically ANDed amp with the corresponding bits of the SRE register and the results ORed to determine the state of the SRQ bit The bits in the SBR do not latch Their state 0 or 1 indicates the state of their associated event register or queue Use the STB query command to read the condition of the SBR Then read the specific event register using the appropriate query command to determine the cause of an event The query commands are listed in Table 5 3 5 8 2 Questionable Event Register The Questionable Event Register QER indicates events that compromise the measurements being made Only two events are indicated Bit 8 Calibration Error Sset if an error occurred during the self test that occurs when the RM100 is first turned on or in response to the TST command Bit 9 Over Range Set whenever the measurement results in an over range error The bits in the QER are latched until reset by reading the register or issuing a CLS command Use the STAT QUES command to read the contents of the QER The state of the QER is reported to the SBR based on the contents of the Questionable Event Enable QEE register The QER bits are ANDed with the corresponding QEE register bits and the results ORed to determine the state of the QSB bit in the SBR Enable the reporting of a QER event b
45. e 4 6 Calibrating Helmholtz Coils and Solenoids The RM100 can be used to calibrate Helmholtz coils and solenoids that are in turn used to generate accurate and known magnetic fields Helmholtz coils and solenoids have many applications including calibrating magnetometers and magnetic field sensors The procedure described below is very general and can be tailored for a specific user s application 1 If possible orient the axis of the coil being calibrated so that it is pointing East West to minimize the ambient field along the axis 2 Place the RM100 sensor at the geometric center of the coil 3 Align the sensor s sensitive axis with the axis of the coil 4 Apply a field by passing a known current through the coil 5 Press the Null key to activate the Null function Record the resulting offset field value 6 Reverse the direction of the current passing through the coil and repeat step 5 7 Subtract the two readings and divide the result by two to determine the value of the actual applied field RM100 User s Manual June 2004 MEDA Inc 18 8 Repeat this procedure for all desired field values 9 Perform a linear regression analysis with the known currents and corresponding measured field values The slope of the linear regression is the coil constant of the coil being calibrated The worst case accuracy of the coil constant measured using this technique is the sum of the accuracies of the current values and the
46. e another Use the following equations to convert from one set of components to the other H Z I X Y D Z Y X R Y X H I R Z D H Y D H X 1 1 2 2 2 2 2 tan tan sin sin cos The following subsection describes how the RM100 can be used to measure the vector components in either of these two coordinate system representations 4 3 Measuring Earth s Magnetic Field We are immersed in a static magnetic field produced by the Earth The presence of this field both helps us and hinders us in the measurement of magnetic fields We are all familiar with compasses The compass needle is itself a magnet and when placed in Earth s magnetic field it points toward the north magnetic pole which coincidentally is very near the geographic North Pole This is a useful property of the Earth s field since it allows us to orient ourselves everywhere on Earth except at the poles themselves RM100 User s Manual June 2004 MEDA Inc 14 4 3 1 Measuring the Vector Components The compass needle only provides us with directional information about the vector pointing to the magnetic north pole The RM100 can be used to measure both the direction and magnitude of the Earth s field vector as well as its North South East West and vertical vector components Follow the steps described below Make sure yo
47. e that surrounds the core signal winding and the excitation winding 6 3 2 Fluxgate Operation A fluxgate sensor converts magnetic fields into an electrical voltage by driving a highly permeable magnetic core alternately between positive and negative magnetic flux density B saturation levels This process and the associated waveforms are illustrated in Fig 6 3 RM100 User s Manual MEDA Inc June 2004 39 Figure 6 3 Fluxgate Sensor Operation An alternating current is applied through the excitation winding This creates a magnetic field that circulates toroidally around the magnetic core This magnetic field causes the flux in the Permalloy to periodically saturate first clockwise and then counterclockwise While the Permalloy is between saturation extremes it maintains an average permeability much greater than that of air When the core is in saturation the core permeability becomes equal to that of air If there is no component of magnetic field along the axis of the signal winding the flux change seen by the signal winding is zero If on the other hand a field component is present along the signal winding axis then each time the Permalloy core goes from one saturation extreme to the other the flux within the core will change from a low level to a high level According to Faraday s law a changing flux will produce a voltage at the terminals of the signal winding which is proportional to the rate of change of flux As the co
48. ed This means that the host and RM100 must have the same network address masked portion of the IP address or be connected through a router To test the network connection using a Microsoft Window operating system RM100 User s Manual June 2004 MEDA Inc 22 1 Select Start gt Run to display the Run dialog 2 Type cmd in the open edit box and press OK 3 In the command window type ping lt IP address gt lt IP address gt is the dot decimal IP address that was entered into the RM100 Setup screen The results of these actions are shown in Fig 5 1 Figure 5 1 Results of pinging the RM100 If you receive a Timeout message instead of the Reply from messages the RM100 and host computer are not able to communicate Check your connections and communication parameter settings You may need to contact your system administrator if you cannot resolve the problem yourself Once you have verified connectivity use the following procedure to test the RM100 This procedure assumes that a Hyper Terminal session has been initiated 1 Select Call gt Disconnect from the Hyper Terminal menu to disconnect from the Ethernet interface 2 Select File gt Properties from the Hyper Terminal menu and verify that the IP address and port number agrees with the RM100 settings and Connect using is TCP IP Winsock 3 Select the Settings tab on the top of the dialog box 4 Click on the ASCII Setup button 5 Check the Send end lines wi
49. een or transferred to a computer using the computer interface 3 8 1 Storing Data in the Data Buffer To store data in the data buffer press the Store key The Mem annunciator will be displayed and data storage will begin immediately Pressing the Store key clears the memory of all previously stored data before it begins storing new data Pressing the Store key a second time stops data storage and turns the Mem annunciator off The Mem annunciator also turns off when the data buffer becomes full Pressing the Shift key followed by the Plot key also stops data storage and starts data plotting Measurement statistics can be displayed while the data is been stored as well as after the data buffer is full Press the Shift key followed by the Store key to display the current measurement statistics for the data in the data buffer The measurement statistics will be displayed in the upper right corner of the screen Repeat this keystroke sequence to remove the measurement statistics from the screen The data buffer is located in volatile memory so the data is lost when the RM100 is turned off Use the Save function see section 3 9 to store the data in non volatile memory for later retrieval using the Recall function 3 8 2 Plotting Data Stored in the Data Buffer An X Y plot of the data stored in the data buffer can be displayed on the RM100 screen in slices of 210 points To plot the data in the data buffer press the Shift key followed by the Plot k
50. efore the accuracy of the actual field is 0 01 of the offset field 1 of the difference field 1 nT 4 4 2 Using the Auto Null for Continuous Measurements Use the Auto Null function to achieve the highest accuracy when making continuous measurements of a DC or slowly changing magnetic field The Auto Null function measures the difference between the ambient field and the nulling offset field three times per second The offset field is updated whenever the difference is more than 1 1 nT The displayed value is the negative of the offset field the difference field The accuracy of the displayed field measurement is 0 01 of the reading 0 2 nT Use the following procedure to make the measurements 1 Align the sensor in the desired direction and secure it 2 Press the Shift key followed by the Offset key The RM100 will first null the field and then go into the Auto Null mode The value displayed will be the measured magnetic field instead of the difference field The magnitude of the field should be within 1 nT of the offset field In the Auto Null mode the RM100 can accommodate changes up to a rate of 300 nT per second If the field should change by 100 nT the RM100 will automatically perform the Null function as if the Null key had been pressed The Auto Null function is only effective for fields up to 100 T To measure fields greater than 100 T use the standard Null function You can use the Store function to recor
51. erface type is not serial use the left or right arrow to change the type to serial 3 Use the down arrow to highlight the BAUD field 4 Use the left or right arrow to select the desired baud rate 5 Press the Escape key to save the changes and return to the main screen The new baud rate is saved in non volatile memory 5 2 2 Connecting to a Computer Connect the RM100 to the serial port of a host computer using a standard RS 232 cable with a male DB 9 connector on one end and a female DB 9 connector on the other end The male end connects to the RM100 and the female end connects to the computer The length of the cable should be less than 50 feet 15 meters 5 3 Preparing for Ethernet Operation The Ethernet interface allows the RM100 to be controlled over a local area network LAN or the Internet The user must set various network parameters before the RM100 is connected to the network These parameters are usually assigned by the system or network administrator The RM100 can also be connected directly to a computer through the Ethernet connector using a crossover cable The following sections describe how to configure the RM100 for network operation This manual assumes that the user is familiar with network architecture and operation as well as with the TCP IP protocol 5 3 1 Choosing a LAN Structure A LAN can be structured as either a private network or an public network A public network is the typical network found in
52. error numbers along with an explanation of what could cause the error 4 Applications This section describes how to use the RM100 to solve typical measurement tasks The RM100 is a single axis fluxgate magnetometer that can be used to measure both the direction and magnitude of a magnetic field vector The first two subsections provide a brief tutorial about magnetic fields The remaining subsections discuss specific measurement situations and recommended measurement methodologies 4 1 Magnetic Field Units The units commonly used within the scientific community to specify the strength of a weak magnetic field are nanotesla nT or gamma Magnetic field magnitudes are also often stated in milligauss mG or microtesla T The strength of a strong magnetic field is usually given in Gauss G Oersted Oe or Tesla T Another unit which is used is the Ampere meter A m These different units of measurement frequently cause confusion among users of magnetic field measuring instruments All of these units are interrelated Only the Oersted and the Ampere meter are proper units for specifying magnetic field strength The other units specify flux density which is related to magnetic field strength through a material property called permeability It so happens that the permeability of air is one 1 in the centimeter gram second cgs system and most measurements are made in air Under this circumstance the flux density magnitude and field
53. ey There must be data stored in the data buffer for this function to work If there is no data in the data buffer the Error annunciator will be turned on This function will also stop data collection and turn the Mem annunciator off Time is plotted along the X axis with the time between data points being 1 3 second The data value in nT is plotted along the Y axis The Y axis scale is automatically adjusted so that all data values can be displayed within the 210 point slice A cursor which is represented by a vertical arrow pointing down is located along the top of the screen The X and Y fields in the lower left corner of the screen indicate the data point and the data value at the cursor location respectively Initially the cursor is located at the start of the plot Use the left or right arrows to change the cursor position The other two fields along the bottom of the screen display the average AVG and peak to peak P P values of the data slice in nT To display the next 210 point data slice press the Shift key followed by the right arrow key To display the previous 210 point data slice press the Shift key followed by the left arrow key To return to normal RM100 operation press the Escape key 3 9 Saving and Recalling Data Stored in the Buffer The data stored in the data buffer can be saved in non volatile memory for later recall The data in the data buffer is not automatically saved in non volatile memory pr
54. hich is the negative value of the measured ambient field Press the Settings key and use the up or down arrows to change the range to the desired value based on the expected change in the ambient field Press the Escape key to return to normal operation Attach the analog output to a recording device and or press the Store key The basic accuracy of the analog output scale factor is 1 For better accuracy use the procedure in section 3 4 6 to calibrate the analog output scale factor before using the analog output to record changes 3 4 6 Calibrating the Analog Output Scale Factors The analog output scale factors for each of the four ranges can be accurately calibrated by using the offset function to generate a very accurate magnetic field The following procedure should be performed in a magnetically quiet area where the measurements will not be disturbed by moving ferromagnetic objects The measurements should be performed as quickly as practical since the Geomagnetic field is constantly changing and could affect the accuracy of the calibration To calibrate the scale factor of the analog output Reset the offset field by pressing the Shift key followed by the Clear key With the sensitive axis of the sensor in the horizontal plane point the sensor east and rotate it slowly in the horizontal plane until the measured field is less than 10 nT Secure the sensor so that it doesn t move Press the
55. ield Units 12 4 2 Vector Nature of Magnetic Fields 13 4 3 Measuring Earth s Magnetic Field 13 4 3 1 Measuring the Vector Components 14 4 3 2 Accurately Measuring the Magnitude of the Earth s Field Vector 15 4 3 3 Monitoring the Earth s Field Magnitude 15 4 4 Using the Null Function to make Accurate Measurements 15 4 4 1 Using the Null Function for a single Measurement 15 4 4 2 Using the Auto Null for Continuous Measurements 16 4 5 Using the Alarm function 16 4 5 1 Screening Material for Magnetic Contamination
56. ields 2 Getting Started 2 1 Unpacking and Inspecting the RM100 Carefully unpack and inspect the RM100 for physical damage Verify that the items received agree with the enclosed packing slip If there are any damaged parts inform the shipping service and MEDA If there are any missing parts contact MEDA RM100 User s Manual June 2004 MEDA Inc 2 2 2 Front and Rear Panels The front panel see Figure 2 1 consists of two elements a Vacuum Florescent Display VFD and a 4x4 membrane keypad The VFD displays the measured data and the RM100 s settings The keypad is used to control the functions of the RM100 The rear pane see Figure 2 2 contains the power input connector the analog output connector the sensor input connector RS 232 connector RJ45 Ethernet connector and a power input fuse DIFFERENCE FIELD OFFSET FIELD SETTINGS LINE KEYPAD STATISTICS DISPLAY Auto MACINTYRE ELECTRONIC DESIGN ASSOCIATES INC RM100 NANOTESTLA METER Settings Offset Setup 1 Alarm 2 3 4 Stats Units Null 5 6 7 8 9 0 OK BS Shift SPC Disp Error Clear Store Recall Local Plot Escape Save RNG 0 1 SMO 1 LPF 10 PLR out IF loc Offset 00 000 0 nT 99999 9 nT CNT 10800 MAX 28990 7 MIN 28711 8 PTP 278 9 AVG 28989 2 Figure 2 1 Front Panel Figure 2 2 Rear Panel RM100 User s Manual MEDA Inc June 2004 3 2 3 Connecting the Senso
57. into two positions for carrying The handle can be locked in place above the case or in front of the case To move the handle disengage it from the left side connection rotate it until it is in the desired position then reengage the handle connection 2 7 Using the Keypad All local operations are controlled using the 4x4 keypad on the right hand side of the front panel The keypad is constructed of membrane switches with tactile feedback There is also audio acknowledgement when a key has been pressed and recognized by the RM100 Some keys such as the Shift key cause an annunciator to be activated The annunciator will appear between the Offset display in the middle of the front panel screen and the settings line at the bottom of the screen The word in the upper left corner of each key indicates the key s main function The word in the lower right corner of each key indicates the key s second function which is activated by pressing the Shift key 3 Front Panel Operations This section describes how to operate the RM100 using the front panel controls Refer to Section 5 for an explanation of how to remotely control the RM100 using an RS 232 or Ethernet connection 3 1 Turn on Self Test The RM100 goes through a self test just after it turns on This test takes several minutes to perform and will cause the display to flash several times The following test sequence occurs 1 Analog to Digital converter test RM100 User s Manua
58. ior to turning the RM100 off 3 9 1 Saving the Data Buffer in Non Volatile Memory To save data stored in the data buffer press the Save key Measurement will be suspended and Saving will be displayed on the right side of the screen while the data is being transferred to non volatile memory RM100 User s Manual June 2004 MEDA Inc 12 3 9 2 Recalling Data Stored in Non Volatile Memory To recall data stored in non volatile memory press the Shift key followed by the Recall key Measurement will be suspended and Recalling will be displayed on the right side of the screen while the data is being transferred from non volatile memory into the data buffer The size of the data buffer will be adjusted based on the number of points transferred Once the data has been transferred it will be available for plotting on the screen see section 3 7 2 computing and displaying measurement statistics and transferring to a computer through the computer interface 3 10 Retrieving Error Messages If an error occurs the Error annunciator will be displayed To retrieve the errors press the Error key An error number will be displayed on the right side of the screen The errors are stored in a buffer in the order in which they occurred first in first out Continue to press the Error key until both the Error annunciator and the displayed error number turn off indicating that there are no more errors to retrieve Section 5 7 lists all of the
59. is being controlled remotely it will display rem otherwise it will display loc The RM100 is placed into the remote mode through the computer interface When in the remote mode the RM100 can be returned to the local mode by pressing the Local key 3 3 Setup Screen The Setup screen is used to set the communication parameters the alarm limits and the size of the data buffer The RS 232 baud rate and the Ethernet parameter settings are saved in EEPROM when the Escape key is pressed which also causes the RM100 to return to the normal measurement display screen The other parameter changes are not saved Press the Setup key to display the Setup screen The TYPE field will be highlighted when the Setup screen is initially displayed Use the up and down arrows to move from one field to another Use the left and right arrows to cycle through the field parameter selections Use the OK key to select those fields for change that require the operator to type in a value Only numerical values are required The numbers in the upper right corner of a key indicate the number that will be typed in when it is pressed during data entry Press the OK key after entering data into a field to indicate acceptance of the new value Press the Escape key to reject the entered value and return to the original value The following subsections describe how to change each setting 3 3 1 Selecting the Computer Interface A computer through either an RS 232 serial connectio
60. itch matrix key pad provides a front panel user interface The columns of the matrix are periodically activated and the rows read by the microprocessor The microprocessor interprets these switch closures as user commands A 256 x 64 dot vacuum fluorescent graphics display provides the user with measurement results plots and other data 6 2 3 Analog Data Filtering and Conversion A 22 bit analog to digital converter ADC converts the analog voltage from the sensor signal conditioner into a digital form that is processed by the microprocessor The signal conditioner analog output is also fed to the input of a programmable low pass filter The low pass filter output is available through a connector on the RM100 back panel The user can also insert a power line rejection filter between the signal conditioner analog output and the low pass filter to reduce unwanted power line signals An 18 bit digital to analog converter DAC generates the voltages that are converted by the neutralization circuit into a current in the neutralization winding to create the offset field RM100 User s Manual MEDA Inc June 2004 37 Excitation Circuit Signal Conditoner Neutralization Circuit 4 Channel 22 bit Analog to Digital Converter Programmable Low Pass Filter Power Line Rejection Filter Temperature Sensor E X E S I G N E U T 18 Bit Digital to Analog Converter TTL to RS232 Converter State Out In Alarm
61. king and Inspecting the RM100 1 2 2 Front and Rear Panels 2 2 3 Connecting the Sensor Probe 3 2 4 Connecting Input Power 3 2 5 Adjusting the Viewing Angle 3 2 6 Adjusting the Carrying Handle 3 2 7 Using the Keypad 3 3 Front Panel Operations 3 3 1 Turn on Self Test 3 3 2 Basic Settings 4 3 2 1 Range
62. l June 2004 MEDA Inc 4 2 Analog magnetometer test 3 Neutralization circuit test 4 100 T range test 5 0 1 T range test 6 1 T range test 7 10 T range test 8 LPF output test 9 PLR output test If an error occurs the ERROR annunciator will turn on and a three second beep will be sounded Press the Error key to determine the cause of the error s An error number will be displayed Refer to Table 5 4 for an explanation of the error The self test stops if any one of the first three tests fails If the ADC or analog magnetometer fails the instrument cannot perform any measurement functions If the neutralizing circuit fails the instrument can still be used to make measurements but any function requiring its use such as nulling will not operate properly The nulling function is used to perform the range tests so these tests will not be performed if the neutralizing circuit is not functioning properly The self test can also be initiated through the remote interface by sending TST After the test is completed a number will be returned indicating the cause of failure if any A zero indicates the RM100 passed all tests See the Troubleshooting section for tests that can be performed by the operator to further determine the nature and cause of any error While the RM100 is performing the Self Test the sensor should remain stationary and in a magnetically quiet area otherwise test errors may occure 3 2
63. layed 6 Place the object to be checked at the prescribed distance from the sensor 7 Rotate the object 360 degrees in all three axes If the alarm sounds it means a limit was exceeded 8 Press the Alarm key to deactivate the Alarm function 9 Repeat steps 4 through 7 for each object tested It may not be necessary to perform steps 4 and 8 between testing objects if the alarm limits are high enough and the ambient field is stable 4 5 2 Checking the Residual Field in a Magnetic Shield To check that the residual field in a magnetic shield is within specified limits 1 Set the alarm limits in the Setup screen see section 3 2 4 2 Place the sensor in the shield at the prescribed specification position 3 Set the RM100 range to 0 1 T see section 3 1 1 4 Press the Alarm key to activate the Alarm function The Al annunciator will be displayed 5 Rotate the sensor 360 degrees in the horizontal plane and then point it vertically If the alarm sounds at any time during these maneuvers then the residual field in the shield exceeds the specified limit 6 Move the sensor to another prescribed specification position and repeat step 5 7 Repeat steps 5 and 6 for all prescribed specification positions 8 Press the Alarm key to deactivate the Alarm function Step 3 of the above procedure assumes that the residual field limits are less than 100 nT If the limits are higher than 100 nT set the range to the appropriate valu
64. n or an Ethernet connection can control the RM100 remotely With the TYPE field highlighted use the left or right arrow to select between serial RS 232 and Ether Ethernet interface modes RM100 User s Manual June 2004 MEDA Inc 6 3 3 2 Selecting the RS 232 Baud Rate The operator can set the baud rate of the RS 232 port to one of five values 9600 19200 38400 57600 or 115200 With the BAUD field highlighted use the left or right arrow to cycle through the allowed baud rates The default baud rate is 9600 3 3 3 Setting the Ethernet Parameters The Ethernet connection uses the TCP IP protocol The RM100 requires a static IP address network mask gateway router address and port number to communicate over the network Initially these parameters are set to default values that are meant for a private network one not connected to the Internet The user must set these parameters to the values appropriate for his or her network These values are usually obtained from the Network Administrator To set the IP address Highlight the IP field Press the OK key This will erase the current value and place a cursor at the beginning of the field Type in the new IP address in dot decimal notation e g 192 168 0 2 If you make a mistake press the BS key to erase the last entry and move back one space Press OK to accept the new value or Escape to return to the original value To set the MASK address
65. nals are attenuated a minimum of 40 dB OUTPut PLReject Returns the current state of the power line rejection filter READ Returns the current value of the difference field in the current units e g 42 1473 Use SENS UNIT to determine the current units SAMPle AVERage Returns the average value of the measurements stored in the data buffer in the current units Returns 0 if the data buffer is empty and generates error 230 Data corrupt or stale SAMPle COUNt lt value gt MIN MAX DEF Sets the size of the data buffer to lt value gt MIN MAX or DEF lt value gt can range from 1 to 16 384 MIN equals 1 MAX equals 16 384 DEF equals 1024 SAMPle COUNt Returns the size of the data buffer SAMPle MAXimum Returns the maximum value of the measurements stored in the data buffer Returns ERR if data buffer is empty SAMPle MINimum Returns the minimum value of the measurements stored in the data buffer Returns ERR if data buffer is empty SAMPle POINTs Returns the number of data points stored in the data buffer SAMPle PTPeak Returns the peak to peak value of the measurements stored in the data buffer Returns ERR if data buffer is empty SAMPle RECAll Equivalent to pressing Shift Recall keys Transfers the data stored in non volatile memory into the data buffer and update the size of the data buffer accordingly RM100 User s Manual June 2004 MEDA Inc
66. nection is convenient for remote control in a single instrument application The Ethernet connection which uses TCP IP protocol is ideal for remote connection over a local area network or the Internet 5 1 3 Single Client Operation Only one client may be connected to the RM100 at a time This is easily controlled when using the RS 232 interface since it only allows for one physical connection When using the Ethernet interface it is possible for two clients to try to connect to the RM100 at the same time The first client to connect will be given exclusive access All other clients will be denied access until the current client disconnects This is done to prevent one client from overriding the commands of another client RM100 User s Manual MEDA Inc June 2004 19 5 2 Preparing for RS 232 Operation 5 2 1 Setting the Communications Parameters The communication parameters for the RS 232 interface are shown in Table 5 1 as set at the factory prior to shipment The host computer and RM100 communication parameters must match for successful communications Table 5 1 RS 232 Communication Parameter Factory Settings Parameter Factory Setting Baud Rate 9600 Parity None Number of Data Bits 8 Number of Stop Bits 1 The baud rate is the only RM100 parameter that can be changed by the user To change the baud rate 1 Press the Setup key The Setup screen will be displayed with the TYPE field highlighted 2 If the int
67. ntegrates and amplifies the base band output and then feeds back the output through a resistor to the signal winding The fed back signal produces a magnetic field inside the sensor which opposes the external field This keeps the field inside the sensor near zero and in a linear portion of the magnetization curve of the ferromagnetic core Under these circumstances the transfer function becomes almost completely determined by the ratio of the feedback resistor to the current to field coil constant of the sensor winding Both of these constants can be very well controlled The consequence of this circuit topology is a highly stable and accurate magnetometer that is insensitive to circuit component variations with temperature or time 6 4 Analog Magnetometer Circuit Configuration The analog magnetometer portion of the RM100 includes the sensor unit excitation circuit signal conditioner and the neutralization circuit Figure 6 5 is a simplified block diagram of the analog magnetometer 6 4 1 Excitation Circuit The excitation circuit consists of a 14 kHz square wave oscillator that provides a reference signal The output of the oscillator is divided by 2 and fed to the input of a power amplifier that drives the excitation winding at 7 kHz RM100 User s Manual MEDA Inc June 2004 41 Figure 6 5 Block Diagram of the Analog Magnetometer Circuit 6 4 2 Signal Conditioner The signal from the sensor is AC amplified and then fed to the
68. othing off LPF 10 Hz PLR out OFF 00 000 nT Also the data buffer is cleared and the size of the data buffer is set to the default value 1024 SRE lt value gt Places lt value gt into the Service Request Enable Register which must be an integer between 0 and 255 The values of bit one and bit six are ignored since they are not used SRE Returns the value stored in the Service Request Enable Register with bits one and six set to zero STB Returns the value stored in the Status Byte Register TST Performs a self test of the RM100 and returns a code indicating the RM100 User s Manual MEDA Inc June 2004 31 Command Parameters Description success or failure of the test The error code corresponds to the condition listed below Number Condition 0 Passed 1 ADC failure 2 Analog Magnetometer failure 3 Neutralization circuit failure 4 100 T range failed 8 10 T range failed 16 1 T range failed 32 0 1 T range failed 64 LPF output failed 128 PLR output failed If the RM100 fails any one of the first three tests the remaining tests are not performed To determine the cause or causes of the failure convert the number to binary Each binary digit corresponds to the failed component For example 48 converts to a binary number 00110000 32 16 Therefore the 1 and 0 1 T ranges failed WAI Non operational in the RM100 Recognized but not executed
69. r Probe The RM100 sensor probe connects to the RM100 through a 50 cable Connect the sensor cable to the sensor input connector on the rear panel of the RM100 The sensor must be connected to the RM100 before turning power ON 2 4 Connecting Input Power The RM100 input power is supplied using an external 7 5 VDC power adaptor The power adaptor will operate from power line voltages of 100 to 240 VAC and frequencies of 60 50 Hz The standard power cord supplied with the RM100 fits North American power outlets Other power cords are available for non North American use Plug the power adaptor into the power line outlet With the RM100 power switch in the OFF position connect the adaptor output into the RM100 power input connector Turn the RM100 power switch into the ON position to turn the RM100 on 2 5 Adjusting the Viewing Angle The RM100 is equipped with two legs on the bottom near the front that can be rotated into the vertical position to tilt the front of the meter up slightly The carrying handle attached to the left side of the case can be rotated downward and under the RM100 to achieve a greater viewing angle Pull the handle along the direction indicated by the handle arrow on the left side of the case until it becomes disengaged Rotate the handle clockwise until it is below the bottom of the case then release the side connection until it reengages 2 6 Adjusting the Carrying Handle The RM100 carrying handle can be placed
70. re permeability alternates from a low value to a high value it produces a voltage pulse at the signal winding output The amplitude of this voltage pulse is proportional to the magnitude of the external magnetic field and its phase indicates the direction of the field The frequency of the signal is twice the excitation frequency since the saturation to saturation transition occurs twice each excitation period RM100 User s Manual June 2004 MEDA Inc 40 6 3 3 Sensor Signal Processing The signal from the fluxgate is an amplitude modulated suppressed carrier signal that is synchronous with the second harmonic of the excitation signal A simplified schematic of the fluxgate sensor signal processor is shown in Fig 6 4 The circuitry to the left of the sensor is called the excitation circuit It consists of an oscillator tuned to twice the excitation frequency a flip flop which divides the oscillator frequency by two and a power amplifier which is driven by the flip flop and in turn provides the excitation current to the excitation winding OSCILLATOR FLIP FLOP PA AMP AMP SYNCHRONOUS DEMODULATOR Rf F C R EXC SIG 2F SENSOR Vo Figure 6 4 Block Diagram of the Fluxgate Sensor Signal Processor The circuitry to the right of the sensor is called the signal channel circuit It amplifies the output from the fluxgate signal winding synchronously demodulates the AC signal using the oscillator signal as a reference i
71. rward while turning clockwise to remove the holder Remove the old fuse and replace it with a Littlefuse 312003 3A fuse or equivalent Reinsert the fuse holder into the fuse case and turn counterclockwise while pressing the folder forward until it locks in place 7 3 Calibration Cycle The RM100 should remain with specifications for at least one year MEDA recommends that the instrument be calibrated annually The RM100 must be returned to MEDA for calibration The special equipment required to calibrate the RM100 is normally not available from a standard calibration laboratory APPENDIX A SPECIFICATIONS RM100 User s Manual June 2004 MEDA Inc Accuracy Specifications Function Range Resolution Accuracy 25 C 5 C Temp Co 0 C 50 C 1000 hrs 25 C 5 C Absolute field 200 T 0 1 nT 0 01 of reading 0 25 of difference 1 nT See offset and difference specification See offset and difference specification Offset field 100 T 0 1 nT 0 01 of reading 0 2 nT 0 5ppm C 10ppm Difference field 100 T 10 T 1 T 100 nT 0 1 nT 0 25 of reading 1 nT 0 25 of reading 1 nT 0 25 of reading 1 nT 1 0 of reading 1 nT 5 0ppm C 25ppm Analog output scale factor 10 Volts FSR 1 1 50ppm C 100ppm Analog output voltage range 10 Volts Low pass filter cutoff frequency 10 50 100 500 1000 Hz 2 of cutoff frequency 100ppm
72. s the error number and short text message of the error stored in the error buffer Error numbers are stored in the error buffer in first in first out order The NEXT is optional SYSTem LOCal Places the RM100 into local mode SYSTem REMote Places the RM100 into remote mode and locks the keypad except for the Local key SYSTem TIME lt hour gt lt minute gt lt second gt Sets the internal RM100 real time clock to the specified hour minute and second SYSTem Returns the RM100 real time clock RM100 User s Manual June 2004 MEDA Inc 30 Command Parameters Description TIME hour minute and second comma delimited SYSTem VERsion Returns the SCPI version to which the RM100 conforms CLS Clears all event registers summarized in the Status Byte Register ESE lt value gt Places lt value gt into the Event Status Enable Register which must be an integer between 0 and 255 ESE Returns the value stored in the Event Status Enable Register ESR Returns the value stored in the Event Status Register and clears the register IDN Returns the RM100 identity string MEDA RM100 nnnnnn n n Where nnnnnn is the serial number and n n is the firmware version OPC Sets the Operation Complete bit in the Standard Event Status Register when parsed OPC Returns an ASCII 1 when parsed RST Resets the RM100 to its power on default state RNG 100 T SMO 1 point smo
73. setting the corresponding bit in the ESE to 1 Use the ESE command to set the bits in the ESE register see Table 5 1 5 8 4 Operation Event Register The Operation Event Status OES register bits correspond to the following events Bit 0 through Bit 7 Unused Bit 8 Filter Settled Indicates that the running average filter has settled Bit 9 Lower Limit Failed Set when the lower limit test fails Bit 10 Upper Limit Failed Set when the lower limit test fails Bit 11 through Bit 15 Unused The bits in the OES register are latched until reset by reading the register or issuing a CLS command Use the STAT OPER command to read the contents of the OES register The state of the OES register is reported to the SBR based on the contents of the Operation Event Status Enable OESE register The OES register bits are ANDed with the corresponding OESE register bits and the results ORed to determine the state of the OSB bit in the SBR Enable the reporting of an ESR event by setting the corresponding bit in the ESE to 1 Use the STAT OPER ENAB command to set the bits in the OESE register see Table 5 1 5 8 5 Clearing the Event and Event Enable Registers The event and event enable registers are cleared when the RM100 is first turned on These registers can be cleared programmatically using the following commands CLS Resets all bits in the Standard Operation and Questionable Even
74. strength magnitude are the same and are sometimes reported using the units interchangeably The relationships between the units are given below 1 nT 1 1 G 105 1 A m 4 x 10 3 Oe 1 T 104 G 1mG 0 1 T The RM100 allows the user to select nT T or mG as the unit of magnetic field strength to display RM100 User s Manual MEDA Inc June 2004 13 4 2 Vector Nature of Magnetic Fields Magnetic fields are vectors At any point in space a magnetic field has a magnitude and a direction This is illustrated in Fig 4 1 z R y x H Z Y X D I Figure 4 1 Vector representations of a magnetic field A vector is usually represented graphically by an arrow which indicates the direction of the vector and has a length which is proportional to the vector magnitude A magnetic field vector can be separated into three vector components X Y Z which are at right angles to one another These are called the rectangular components of the vector The magnitude R of the vector is determined by squaring the component vector magnitudes summing the squares and then taking the square root of the sum The magnetic field vector can also be represented in polar coordinates by two angles I and D and a magnitude R In Fig 4 1 H is the component of the magnetic field vector in the X Y plane which is usually chosen to be the horizontal plane The rectangular and polar components of the vector are related to on
75. t Registers STAT PRES Resets all bits in the Operation and Questionable Event Enable Registers ESE 0 Resets the Event Status Enable Register RM100 User s Manual June 2004 MEDA Inc 36 6 Theory of Operation 6 1 Introduction This section provides a description of how the RM100 works The first subsection gives an overview of the RM100 Subsequent sections go into greater detail The objective is to provide sufficient detail for you to understand how best to use the RM100 in your applications 6 2 Overview Figure 6 1 is a block diagram of the RM100 The RM100 is divided into two major components the Sensor Unit SU and the Electronics Unit EU The SU contains the fluxgate sensor that includes three windings the excitation winding the signal winding and the neutralization winding The EU contains the circuitry needed to excite the sensor process the sensor signal display the results to the user and respond to user front panel and remote command 6 2 1 Embedded Microprocessor An RCM2200 microprocessor controls the RM100 functions It responds to front panel keypad commands and commands received through either the RS 232 serial interface or the Ethernet interface The RM100 firmware is stored in a 512 K flash memory The flash memory is also used to store buffer data in response to the Store command A 512K RAM is used to store temporary data 6 2 2 User Interface The front 4 x 4 membrane sw
76. th line feed and Echo typed characters locally boxes 6 Click OK twice to return to the main screen 7 Select Call from the Hyper Terminal Call main menu and then click on Call to connect to the RM100 Connected will appear on the message bar at the bottom of the Hyper Terminal screen 8 Send the following command SYST REM lt CR gt The lt CR gt represents a carriage return which is generated by pressing the Return key 9 Hyper Terminal should echo the command The IF field on the front panel of the RM100 should change from loc to rem RM100 User s Manual MEDA Inc June 2004 23 12 Send the following command IDN lt CR gt The RM100 should respond with MEDA RM100 nnnnnn n n nnnnnn is the RM100 s serial number n n is the firmware version The ERROR annunciator will be turned on if an error occurred Use the SYST ERR command to retrieve the error message describing the cause of the error section 3 10 explains how to retrieve error messages from the front panel 5 5 Command Processing The following sections describe how the RM100 processes commands received through the computer interface and what it sends back to the computer interface in response to the command The RM100 uses version 1999 0 SCPI Standard Commands for Programmable Instruments syntax described in the SCPI Consortiums standards These standards can be obtained from SCPI Consortium 2515 Camino del Rio South Suite 340 San Diego CA 92108
77. u are outside and at least twenty feet away from any magnetic object anything made from iron or steel 1 Tape a piece of paper to a level surface made from non magnetic material Place the probe on the paper 2 Set the RM100 on the 100 T range and rotate the probe for a zero reading Reduce the range to 0 1 T and fine tune the angular position by rotating the sensor for the lowest reading possible 3 Draw a straight line on the paper along the edge of the probe 4 Use a protractor or right angle triangle to draw a line at 90 degrees to the first line Align the probe edge along this line with the probe arrow pointing approximately north press the Null key and record the RM100 offset reading This is the negative value of the horizontal component H of the Earth s field 5 Orient the probe in the vertical direction with the end flat against the surface where the two lines cross Press the Null key and record the RM100 offset reading This is the vertical component Z of Earth s field 6 Compute the total field magnitude 2 2 Z H R 7 Compute the inclination of the field H Z I arctan radians The first line drawn on the paper is the East West direction The second line is the North South direction The Inclination angle is the angle between the Earth s magnetic field vector and the horizontal plane A positive reading when measuring H indicates the direction of the north magnetic pole Table
78. y The standard rejection frequency is 60 Hz 50 Hz is optional 7 Maintenance The RM100 requires very little maintenance There are no user adjustments When the RM100 is turned on it performs a self test to determine the health of the instrument This self test can also be initiated remotely through the RS 232 or Ethernet connection using the TST command The RM100 should be in an area that is magnetically static during the test to prevent false error indications In the event of a failure the instrument should be returned to MEDA for diagnostics and repair with a list of all error codes that were returned by the RM100 after the self test 7 1 Probe Precautions The health of the probe is very important for the reliable and accurate performance of the RM100 Do not expose the probe to fields greater than 500 T 5 Gauss The sensor could be magnetized causing a shift in zero field readings that will affect instrument accuracy The internal structure of the probe is fairly rugged but it does contain some structure that can be damaged by physical abuse This damage can affect sensor alignment and neutralization field performance The probe is not waterproof and should not be place in water The probe should be protected from moisture penetration if measurements are to be made in inclement weather 7 2 Fuse Replacement The RM100 has one fuse that is accessible from the rear panel If the fuse needs to be replaced press the fuse holder fo
79. y setting the corresponding bit in the QEE to 1 Use the STAT QUES ENAB command to set the bits in the QEE see Table 5 1 RM100 User s Manual June 2004 MEDA Inc 34 Figure 5 2 RM100 Status Register Structure RM100 User s Manual MEDA Inc June 2004 35 5 8 3 Standard Event Status Register The Standard Event Status ESR register bits correspond to the following events Bit 0 Operation Complete OPC Indicates that all pending operations are complete This bit is set only in response to the OPC command Bit 1 Not used Bit 2 Query Error Not used Bit 3 Device Dependent Error Not used Bit 4 Execution error Set if there was an error in executing a command Bit 5 Command Error Set when there was an error in the command sent to the RM100 Bit 6 User request Not used Bit 7 Power On PON This bit indicates that the RM100 was turned off and then back on since the last time this register was read The bits in the ESR are latched until reset by reading the register or issuing a CLS command Use the ESR command to read the contents of the ESR The state of the ESR is reported to the SBR based on the contents of the Standard Event Status Enable ESE register The ESR bits are ANDed with the corresponding ESE register bits and the results ORed to determine the state of the ESB bit in the SBR Enable the reporting of an ESR event by

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