hp3478a multimeter - University of California, Berkeley
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1. HEWLETT PACKARD HP 3478A Digital Multimeter Service Manual 478A U SECTION Ill OPERATION 3 1 INTRODUCTION 3 2 This section has the information and instructions for the operation of the 3478A Multimeter showing front panel and remote operation The information is an abbreviated description of the operation and is writ ten for a Service Trained Person rather than an Operator For more complete operating instructions refer to the 3478A s Operators Manual To familiarize yourself with the front and rear panel features or for a review of instrument operations refer to Figure 3 1 3 3 The Operation Section is separated into the follow ing major areas General Information Front Panel Operation Shifted Operation Miscellaneous Opera tion and Remote Operation HP IB It is suggested that you read the Remote Operation Chapters last since you need to know the other operations to understand the remote operations The major areas are as follows a General Information paragraph 3 4 Title Paragraph AC Power Operation 3 5 Turn On 3 7 Display 3 10 Input Terminals 3 12 Input Terminals Cleaning 3 15 b Front Panel Operation paragraph 3 17 Title Paragraph DC Volts Measurements 3 18 AC Volts Measurements 3 22 Resistance Measurements 3 26 DC Current Measurements 3 30 AC Current Measurements 3 34 Ranging 3 38 Triggering 3 43 c Shifted Operation paragraph 3 50 Title Paragraph General 32. 3 22 AC Volts Measurements 3 23 The 3478A uses a True RMS AC to DC Converter to measure ac voltages from 1uV to 300V in four ranges 300mV 3V 30V and 300V The response of the con verter is from 20Hz to 100KHz on all ranges to 300KHz on the 30V Range only All ranges are protected from input voltages up to 450V peak Select the AC Volts Function for ac volts measurements by pressing the v button 3 24 The AC to DC Converter changes the ac input voltage to dc volts which is then measured by the 3478A s A D Converter All ranging is done in the AC to DC Converter applying the same voltage value to the A D Converter for all full scale inputs 3 25 When the AC Volts Function is selected the right side of the display shows MVAC or VAC depen dent on the range selected The reading can be displayed either as a 54 4 or 3 digit reading dependent on the selected Number of Digits Displayed see paragraph 3 54 A 6 second delay is also applied in the ACV Function before a reading is taken also during a range change Refer to Table 1 1 or Table 4 1 for the AC Volts Function s accuracy specifications 3 26 Resistance Measurements 3 27 The 3478A is able to make resistance measurements from 0001 ohms to 30M ohms in seven ranges The ranges extend from the 30 ohm to the 30M ohm range All ranges are protected from input voltages up to 350V peak Resistance measurements can be made using either the 2 Wir
3. display can also show alphanumeric messages sent remotely The four characters to the right show the function and to a certain extent the range and the 8 characters to the left show the reading e g 12 3657 MVDC An OVLD is displayed if the input is out of range for the selected range and function 3 12 Input Terminals 3 13 The 3478A has one set of Input Terminals on the front panel and one set on the rear panel The front panel terminals consist of an INPUT HI INPUT LO Q SENSE HI Q SENSE LO and A Amps terminal Except for the A terminal the rear panel has the same set of terminals The two sets of ter minals are selected by the Front Rear Switch located on the front panel The front terminals are selected with the switch out and the rear with the switch in 3 14 The INPUT HI and LO Terminals are used for measuring dc volts ac volts and resistance in the 2 Wire Ohms configuration Refer to Figure 3 2 for a typical connection The Q SENSE HI and Q SENSE LO Terminals in conjunction with the INPUT Terminals are used in the 4 Wire Ohms configuration Refer to Figure 3 4 for a typical ohms connection The A Amps Terminal with the INPUT LO Terminal is used to N SENSE INPUT OO OO 3A 250Y Figure 3 2 Typical Input Measurement Connection N SENSE INPUT 4 WIRED 2 WIRE Figure 3 3 Typical Current Measur
4. 2 or 3 1 2 digit reading dependent on the selected Number Of Digits Displayed see paragraph 3 54 Refer to Table 1 1 or Table 4 1 for the AC Current Function s accuracy specifications 3 38 Ranging 3 39 The 3478A has two range modes Manual and Autorange Manual ranging is selected by pressing the AUTO MAN button if the 3478A is in Autorange or by pressing either the 4 gt or X gt buttons The M RNG annunciator on the display then turns on The following explains the different range modes 3 40 Uprange The 3478A upranges to the next higher range each time the gt button is pressed The highest selectable range depends on the function selected e g 300V for the AC Volts and DC Volts Functions If a function is selected with its highest range lower than the previous range the multimeter defaults to the new highest range 3 41 Downrange The 3478A downranges to the next lower range each time the X gt button is pressed The lowest selectable range depends on the function selected e g 30mV for the DC Volts Function If a function is selected with its lowest range higher than the previous function the multimeter defaults to the new lowest range 3 42 Autorange The 3478A selects the optimum range when this mode is selected The mode is selected when the 3478A is first turned on or by pressing the AUTO MAN button if in Manual Range If Autorange is enabled the 3478A upranges when the reading is at or above
5. 3478A Addressing 3 93 HP IB requires that each device on the Bus needs to be identified as a Listener or a Talker in order to ex ecute the Bus Messages and commands Because of this each device has its own unique listen and talk ad dress The address of the 3478A is set by the Address Switch on its rear panel Setting the 3478A s Listen Ad dress also sets its Talk Address 3 94 The address switch is an eight section DIP switch with five sections used for addressing The switch is shown in Table 3 5 The allowable address settings are also listed in Table 3 5 The factory address setting of the 3478A is decimal 23 refer to Section II of this manual for the switch setting 3 95 Instrument address commands sent by the con troller are usually in this form universal unlisten device talk device listen The universal unlisten com mand removes all listeners from the Bus to allow only the addressed listener s to receive data The data is sent by a talker which is designated by the device talk com mand 3 96 Talk Only Mode No Controller 3 97 The 3478A s Talk Only Mode allows the multimeter to send measurement data to an external device like a printer without a Bus controller The multimeter is placed into the Talk Only Mode by setting the five address switches on the rear panel DIP switch to 1 set only the five address switches to the up position Measurement data is the
6. dd is the address code of the instrument 3 9 Once the Self Test is completed the 3478A goes to its turn on state which is FUNCTION 2 2052 a aces DCV RANGE 2 2202 geet a AUTO TRIGGER INTERNAL AUTOZERO 2 005 ON NUMBER OF DIGITS DISPLAYED 5 3 10 Display 3 11 The Display is a 12 character alphanumeric Liq uid Crystal Display LCD with 12 annunciators The display is normally used to show readings however the 3 1 Operation 3478A 3478A DIGITAL MULTIMETER HEWLETT PACKARD N SENSE INPUT 4 WIRE 2 WIRE ES Eiza be gt NGEZN I Ea a I ag HAN AUTO a TEST gs 4 WIRE S EA Gates Lak Ce be Al ALL TERM 500V HAX al WARNING FoR PROTECTION FROM ELECTRICAL SHOCK POWER CORD GROUND N SENSE 4 WIRE INPUT 2 WIRE OMO IVT Oe HEWLETT PACKARD CO MADE IN USA MUST NOT BE DEFEATED BT TRI G Vv oe un 2619A34899 ALL TERM 5 0Vpk MAX poe i 1 V 120V 220V 240V O oO jei eige4el leone 1 5 Hz 6 604z 250mAT 125mAT Use the measurement keys along the top row to select the type of measurement you want to make The 12 character alphanumeric display includes 12 dedicated annunciators The display is read directly in engineering units i e MV for
7. milli volts MOHM for Meg ohm resistance etc If the blue key is pressed before another key the function shown above that key is executed These terminals are used for the voltmeter sense leads when making 4 wire ohms measurements These terminals are the voltmeter and 2 wire ohms input 4 wire ohms source current terminals This is the Amps input terminal and is used with the INPUT LOW terminal 3 Amp fuse protected Oo When this switch is out the front panel input terminals are selected If the switch is in the rear panel terminals are used 3478A 3 1 These keys are used to select special operating features of the 3478A The blue shift key allows for selecting the SHIFTED functions of the bottom row of keys The Internal Trigger is selected by this key In this mode the 3478A triggers itself Autozero is a function that allows you to enable or disable the in ternal zero correction circuitry Pressing the Single Trigger key causes the 3478A to take one reading and wait for the next trigger impulse This impulse can come from either the Single Trigger key or the External Trigger input rear panel BNC The Test Reset key performs an internal self test then resets the 3478A to its turn on state Any errors in the seif test are noted in the display The front panel SRQ Service Request key is an HP IB opera tion that enables you to manually interrupt the controller This key is enabled by s
8. 303099 and downranges at or below 027000 delete one or two zeroes from the numbers for the 4 1 2 and 3 1 2 Digit modes respec tively The numeric range points are irrespective of decimal placement Refer to Figure 3 5 for the autorange points the example is for the DCV Function other functions are similar 3 43 Triggering 3 44 The 3478A has three local trigger modes Inter nal Single and External In addition to these a Hold 3 5 Operation a aM 1 N 1 1 DOWNRANGE POINTS i 1 i 1 i 1 1 D 1 1 yn H L i i i H H i i INPUT LEVEL 3478 3 5 Figure 3 5 Autoranging Points and a Fast trigger mode can be selected but only over the HP IB remote operation When the multimeter is triggered the right most digit on the display blinks showing that the display is updated The following paragraphs explain the trigger modes 3 45 Internal Trigger In this mode the measurement cycle is internally initiated and the 3478A makes the measurements at the maximum reading rate The Inter nal Trigger is selected at instrument turn on or by press ing the INT TRIG button 3 46 Single Trigger In this mode a measurement cycle is initiated each time the SGL TRIG button is pressed When the button is initially depressed the 3478A in itiates a measurement cycle and then places the multimeter in the Single Trigger Mode If the button is pressed during a measurement cycle while in the Single Tr
9. 51 Number Of Digits Displayed 3 54 Autozero 3 57 Self Test Reset Operation 3 60 Calibration 3 63 d Miscellaneous Operation paragraph 3 66 Title Paragraph Voltmeter Complete 3 67 e Remote Operation paragraph 3 69 Title Paragraph General 3 70 3478A Response to Bus Messages 3 74 3478A Addressing 3 92 Talk Only Mode No Controller 3 96 3478A HP IB Programming 3 98 Advanced programming 3 117 3 4 GENERAL INFORMATION 3 5 AC Power Operation 3 6 Before connecting ac power to the 3478A make sure the power source matches the power requirement of the multimeter as marked on the rear panel If the in strument is incompatible with the power source refer to Section II of this manual for power requirement modification 3 7 Turn On 3 8 When the 3478A is first turned on the multimeter goes through an Internal Test routine During the test the instrument displays SELF TEST and when the test is completed and it passes the instrument displays SELF TEST OK If the Self Test fails refer to Section VII of this manual for troubleshooting information For more information on the Self Test refer to paragraph 3 60 NOTE For 3478As with serial numbers 2301A03760 and below or any instruments that have the Revision B ROM U502 installed the instru ment displays its remote HP IB address for about one second instead of SELF TEST OK The address is displayed as HPIB ADRS dd where
10. Register as a true condition They will not cause the SRQ Message to be output For example suppose the Front Panel SRQ condition is the only one set in the SRQ Mask If the Data Ready condi tion is true but not Front Panel SRQ no SRQ Message 7 e s oa Jus 2 br oo Power On u Service Request Bit Invalid Calibration Front Panel SRO Data Ready Bit Always O Syntax Error Internal Error Figure 3 6 Status Byte Operation Table 3 4 Status Byte Definitions Octal Decimal Definitions Code Code Data Ready Indicates to the con troller that measurement data is ready to be output The Require Ser vice Message and bit is cleared when the controller begins to accept the data or when the reading is no longer available See paragraph 3 114 This bit is always at O O high Syntax Error This shows that an in valid Program Code s has been sent to the 3478A e g F9 Internal Error Shows that a failure inthe 3478A is detected This may be a failure in the Self Test Routine see paragraph 3 60 the A D Con verter or a checksum error in the Calibration RAM checked every time a reading is taken More infor mation can be obtained by reading the 3478A s error register See paragraph 3 120 Front Panel SRQ This bit is set when the 3478A s Front Panel SRO button is pressed See paragraph 3 115 Invalid Calibration When this bit i
11. automatically set except bit 6 when any corresponding require service condition is true For example you wish to know if the multimeter has received an incorrect program code Syntax Error or has an internal failure Internal Error If the condi tions are true bits 2 and 3 of the Status Byte are set but no Require Service Message is output The message will not be output until the SRQ Mask is set to the cor responding bits of the Status Byte which are are bits 2 and 3 Since the mask is to be set in octal the resultant code for the bits is 14 The mask is set by sending Mdd where dd is the octal code for the bits This is shown in the following example U 7 M14 universal unlisten command set mask controller talk address where 14 is the 3478A listen address octal code for bits 2 and 3 3 104 Only bits 0 to 5 can be set by programming the SRQ Mask Bit 6 of the Status Byte is set whenever the Require Service Message is output and bit 7 is set by the Power On SRQ switch on the rear panel see paragraph 3 106 Because of this only a two digit octal code 00 3 11 Operation Table 3 6 3478A Program Codes Program Description Code DC Volts AC Volts 2 Wire Ohms 4 Wire Ohms DC Current AC Current Extended Ohms see paragraph 3 118 FUNCTION most sensitive range on any func tion 30mV DC or most sensitive range on any other function 300
12. case letters generate characters which do not resemble the letters Commas periods and semicolons can go between characters The ASCII characters can be sent in two different modes The following paragraphs explain the two modes 3 108 In one display mode the display is continuously updated This is enabled by program code D2 e g D23478A DMM where 3478A DMM is the message displayed In this mode the annunciators con tinue to be updated If more than 12 characters are sent to the display the extra characters are ignored until a control character is received If the control character is different than HT Horizontal Tab VT Vertical Tab LF Line Field CR Carriage Return or FF Form Feed a Syntax Error is generated A D2 code locks the display until a D1 Selects Normal Display is sent a CLEAR message is sent an error condition oc curs or a front panel button is pressed 3 109 The other display mode is selected by sending code D3 This mode is the same as the previous mode except the display is not updated and all annun ciators are turned off The text on the display remains on for about 10 minutes and then the display goes blank The display can be restored by sending any of the display codes D1 D2 or D3 or by pressing the LOCAL button if not disabled by the LOCAL LOCKOUT Message 3 110 Home Commands The Home Commands when sent to the 3478A over th
13. e 4 1 2 or 3 1 2 Digit mode the 5th and or 6th digits will be output as zeroes An overload condition whether plus or minus will be output as 9 99999E 9 If a different output is re quested Binary Front Rear Switch position etc the other output supercedes the reading If a data transfer is interrupted while being output the 3478A continues the output wherever it left off when addressed again This partial output or any output can be disabled by a Group Execute Trigger GET Clear Message DCL or SDC sending any valid program code or pressing the LOCAL Shift and TEST RESET buttons on the front panel 3 113 Front Rear Switch Position The 3478A s Front Rear Switch position can be remotely determined by sending program code S to the multimeter and then reading its output If 0 CR LF is output the switch is set to Rear and if 1 CR LF is output the switch is set to Front 3 114 Data Ready Feature The Data Ready feature of the 3478A when enabled outputs a Require Service Message SRQ after each completed measurement cy cle Before the message can be output bit 0 of the SRQ Mask must be set This is done by sending program code MO1 bit 0 of the Status Byte and Status Register When the Require Service Message is sent the front panel SRQ annunciator turns on and bit 0 of the Status Byte is set The SRQ condition remains until the data is read by t
14. e HP IB are used to set the 3478A into a predefined operating state The pro gram code is Hn where n is the number which 3478A defines the state The following lists the home com mands and the corresponding operating states a HO Command The instrument state for this com mand is as follows FUNCTION c cece eee eee nn DCV F1 Rangere ens 30mV Auto R 2RA Trigger Hold T4 Number of Digits Displayed 4 1 2 N4 AULOZETO ccc cece cece eee een On Z1 In addition the 3478A s External Trigger is disabled and the instrument is set into the lowest range R 2 before Autorange is selected Also any data reading output to the Bus or the front panel is erased when the home command is sent The corresponding program codes of the instrument state are FIT4R 2RAZIN4 b Hl Command DCV This command is the same as the HO command except a trigger occurs and the resultant output can be read The corresponding pro gram codes are F1R 2RAZ1N4T3 c H2 Command ACV The same as the H1 command except the selected function is AC Volts The corresponding program codes are F2R 2RAZINAT3 d H3 Command 2 Wire Ohms Same as the H1 command except the selected function is 2 Wire Ohms The corresponding program codes are F3R 2RAZIN4T3 e H4 Command 4 Wire Ohms Same as the H1 command except the selected func
15. e or 4 Wire ohms configuration which are selected by the 2 WIRE Q and 4 WIRE Q but tons respectively Refer to Figure 3 4 for the correct ohms connections 3 28 Resistance measurements are made by applying a known current generated by the 3478A to the unknown resistance The resultant voltage drop is then measured by the 3478A s dc circuitry Input Circuitry and A D Converter In the 2 Wire Ohms Function the voltage drop is measured across the HI and LO INPUT Terminals In the 4 Wire Ohms Function the voltage is measured across the HI and LO Q SENSE Terminals The Ohms Current Source generates the known current which is applied to the unknown resistance in both 3 4 3478A UNKNOWN RESISTANCE Rx 3A 250V i FUSE 2 WIRE OHMS MEASUREMENT UNKNOWN RESISTANCE Rx 4 WIRE OHMS MEASUREMENT Figure 3 4 Ohms Connections ohms functions from the HI INPUT Terminal The current values are as follows Range Current 30 ohm 1mA 300 ohm ImA 3K ohm ImA 30K ohm 100uA 300K ohm 10uA 3M ohm 1uA 30M ohm luA 3 29 When an Ohms Function is selected the right side of the display shows either OHM KOHM or MOHM dependent on the range selected In addi tion the 2 Q annunciator is on for the 2 Wire Ohms Function and the 4 Q annunciator is on for the 4 Wire Ohms Function The ohms reading can be displayed either as a 5 1 2 4 1 2 o
16. ement Connection measure ac or dc current Refer to Figure 3 3 for a typical current connection 3 15 Input Terminals Cleaning 3 16 The high input impedance of the 3478A requires that the area surrounding the multimeter s Input Ter minals front or rear must be free of leakage causing paths e g dirt fingerprints etc The paths can be removed by using a soft cotton swab dipped in isopropyl alcohol 3 17 FRONT PANEL OPERATION 3 18 DC Volts Measurements 3 19 The 3478A is able to make dc volts measurements from luV to 300V in five ranges 30mV 300mV 3V 30V and 300V All ranges are protected from input voltages up to 450V peak Select the DCV Function for dc volts measurements by pressing the v button 3 20 In the DC Volts Function ranging is done in the Input Circuitry of the 3478A The result is that the input to the A D Converter which changes the voltage to digital information has the same value in all ranges for 3 3 Operation all full scale inputs e g 10V input to the A D for 30mV 300mV 3V etc inputs to the 3478A 3 21 When the DC Volts Function is selected the right side of the display shows MVDC or VDC depen dent on the range selected The reading can be displayed either as a 5 1 2 4 1 2 or 3 1 2 digit reading depen dent on the selected Number Of Digits Displayed see paragraph 3 54 Refer to Table 1 1 or Table 4 1 for the DC Volts Function s accuracy specifications
17. erations shifted and unshifted An unshifted operation AUTO MAN INT TRIG etc is normally selected by pressing a single button A shifted operation is done by first pressing the blue SHIFT button on the right end of the upper row of buttons and then pressing one button on the lower row To select a new shifted operation press the blue Shift button again and the button for the new operation Table 3 1 lists the shifted operations and corresponding buttons The shifted operations are also shown in blue lettering above the buttons 3 53 When the blue Shift button is pressed the SHIFT annunciator on the display is on The annun ciator remains on until a different button is pressed Table 3 1 Shifted Operations Shifted Select Description Of Operation Button Operation 3 Digit Disp AUTO MAN Selects 3 Digits Displayed see paragraph 3 54 AN Selects 4 Digits Displayed see paragraph 3 54 Selects 5 Digits Displayed see paragraph 3 54 Turns Autozero on or off see paragraph 3 57 Places the 3478A into its Internal Test Mode see paragraph 3 61 Displays the 3478A s cur rent HP IB Address Code see paragraph 3 92 Places the 3478A into the calibration mode see Sec tion IV of this manual 4 Digit Disp 5 Digit Disp Sr Az INT TRIG Test Reset SGL TRIG Adrs SRQ Cal LOCAL 3 54 Number Of Digits Displayed 3 55 The 3478A can display readings in either 5 1 2 4 1 2 or 3 1 2 dig
18. etting the SRQ mask Figure 3 1 3478A Front and Rear Panel Features 3 2 3478A 3478A The 3478A HP IB Address is displayed when the Address key is pressed The Local key returns the 3478A to front panel control from the REMOTE mode The 3478A features total electronic calibration The Cal key is used as part of that procedure See Section IV 8 The range keys are used to select the proper range for the measurement Press any of the keys to select the manual range mode Note the M RNG annunciator in the display The Auto Man key will return the meter to autorange 10 The SHIFTED functions of the range keys are used to select alternate numbers of display digits Operation The Rear Input Terminals are only used in the DC Volts AC Volts and Ohms Functions They are selected with the werner Front Rear Switch in the in position 12 The External Trigger connector is used to externally trigger the 3478A when in the Single Trigger mode 3 HP IB Connector The Voltmeter Complete Connector outputs a pulse after each measurement cycle 1 The Fuse is 250mA for the 100V and 120V operation or 125mA for the 220V and 240V operation 18 The Option Label shows the instrument s power option M These switches select the 3478A s HP IB Address the Power On SRQ feature and correct power line frequency 50Hz 60Hz Figure 3 1 3478A Front and Rear Panel Features cont d
19. h 3 119 Calibrate see Section IV of this manual Read the Error Register See paragraph 3 120 Clears Status Register Set SRQ Mask Mdd where dd is the octal code of the bits Front Rear Switch Position O Rear 1 Front 3478A 77 can be sent to program the mask The mask can be cleared by sending M00 Remember the mask is on ly set to output a Require Service Message not the Status Byte for a certain SRQ condition 3 105 Clearing Status Register Status Byte Bits 2 through 5 and 7 of the register can be cleared by sending program code K and by a device CLEAR message Bit 0 Data Ready is not cleared since it represents the 3478A s current status the bit is cleared when the 3478A outputs its reading Bit 6 is the SRQ bit which can be cleared by a Serial Poll or if the SRQ Mask is set to 00 3 106 Power On SRQ This feature is enabled by set ting the Power On SRQ switch to On switch 3 on the rear panel in the up position When the feature is en abled the 3478A Requires Service generates an SRQ each time power is cycled or a reset condition is generated by the instrument e g due to an instrument failure or selecting the Self Test 3 107 Sending Data to the Display Up to 12 ASCII characters can be displayed at a time by the 3478A s display The legal characters are decimal 32 through 95 of the 128 ASCII characters Only upper case letters and numbers can be displayed Lower
20. has failed its internal RAM self test U C ROM FAIL The 3478A has failed its internal ROM self test indicating an error in the ROM CAL RAM FAIL An attempt to write to the Calibration CMOS RAM was unsuccessful UNCALIBRATED The Calibration CMOS RAM has an incor rect checksum showing that calibration is needed A D LINK FAIL The internal CPU A D Controller is unable to communicate with the A D Converter A D SLOPE ERR The A D Converter is unable to do a proper conversion A D TEST FAIL The A D Converter has failed its self test 3 63 Calibration 3 64 The 3478A does not have any adjustments to calibrate the instrument calibration is done elec tronically A known good calibration source is applied to the multimeter and the value of the known source is entered into the instrument A reading is then taken and compared with the value entered A Calibration Cons tant is calculated from the entered value to correct the reading to the known value and then stored into memory The correct readings are calculated using the constants and then displayed 3 65 There are two steps in calibrating the 3478A First the front panel Calibration Switch has to be set to 3 7 Operation CAL ENABLE Second the blue Shift button and the LOCAL CAL button have to be pressed for each calibration step e g press the buttons for the DC Volts Function s zero calibration and pre
21. he 3478A must be in remote and listen to receive the codes the RMT and LSTN annunciators are on when the 3478A is in remote and listening An example is as follows Operation CMD MODE DATA MODE U7 F1 RA T3 universal unlisten command controller talk Single Trigger address Autorange 3478A listen address DCV Function 3 102 The Program Codes are a series of 7 bit ASCII characters the parity bit is ignored All lower case characters spaces commas and semicolons are ignored they may be used with the codes as separators All null characters carriage return line feed form feed vertical tab and horizontal tab characters are also ignored Other characters which are not included in Table 3 6 cause a Syntax Error bit 2 in the Status Register set In addition a Syntax Error is caused if the characters are sent in a different order than shown in the table e g 1F causes a Syntax Error Do not send program codes W and or X to the 3478A These codes can under certain conditions uncalibrate the instrument The letters W and X can however be sent behind program codes D2 or D3 which are used to send text to the display see paragraph 3 107 3 103 Programming the SRQ Mask The SRQ Mask must be set for the 3478A to output a Require Service Message Setting the SRQ Mask will not set the bits in the Status Byte these bits are
22. he controller or a Serial Poll is done 3 115 Front Panel SRQ The Front Panel SRQ feature of the 3478A outputs a Require Service Message SRQ each time the Front Panel SRQ button is pressed Before the message can be output bit 4 of the SRQ Mask must be set This is done by sending program code M20 bit 4 of the Status Byte and Status Register Once this is done the Require Service Message will be output and the front panel SRQ annunciator turns on whenever the SRQ button is pressed The SRQ condi tion remains until a Serial Poll is done by the controller 3 13 mm Operation 3 116 Fast Trigger This trigger mode can only be selected over the HP IB It is the same as the Single Trigger except the delays in the AC Volts Function AC Current Function and the high Ohms Ranges are omit ted The mode can be selected by sending program codes T5 3 117 Advanced Programming 3 118 General The following paragraphs have ad vanced programming information for the 3478A It in cludes Extended Ohms Operation Reading the Binary Status Byte and Reading the Error Register 3 119 Extended Ohms Operation This operation or function is only available over the HP IB and is used to measure resistance above 30M ohm The function is selected by sending program code F7 or H7 Home Command see paragraph 3 110 The 3478A is set to the 2 Wire Ohms Function and the 30M ohm Range A 10M ohm resistor is connected i
23. igger mode the 3478A starts a new measurement cy cle When the cycle is completed a new cycle can then be initiated by pressing the Single Trigger button 3 47 External Trigger This mode is selected by press ing the SGL TRIG button and operates the same as the Single Trigger mode The difference is that the 3478A can be triggered from the External Trigger input on the rear panel The input is TTL logic compatible and the trigger pulse should be at least 100nS wide The 3478A is triggered on the negative edge of the TTL pulse 3 48 Trigger Hold In this mode no triggering is done by the 3478A no measurement cycle is initiated This mode can only be selected using the 3478A s remote operation 3 49 Fast Trigger This trigger is the same as the Single Trigger except the delays in the ACV and ACI Func tions and high Ohms Ranges are omitted This trigger can only be selected using the remote operation NOTE When the 3478A is in the Single Trigger mode and an attempt is made to change 3 6 3478A range or function the left portion of the display goes blank except for the decimal point until another reading is taken instru ment triggered 3 50 SHIFTED OPERATION 3 51 General 3 52 The Shifted Operation of the 3478A is used to ex pand the capabilities of the multimeter using the same number of front panel pushbuttons This is done by us ing the bottom row of front panel buttons for two dif ferent op
24. isten if Addressed to Talk No Extended Listener No Extended Talker Service Request Capability Remote Local Capability with Local Lockout No Parallel Poll Capability Device Clear Capability Device Trigger Capability No Controller Capability 3A 76 Data The Data Message is used to transfer infor mation between the 3478A and the controller f a The message is used to send data to the multimeter fand consists primarily of set up information e g DC olts 30V Range etc The 3478A is the Listener and ithe controller is the Talker b The message is also used by the controller to receive data from the 3478A This includes the multimeter s output readings and status information f In this case the 3478A is the Talker and the controller is f the Listener 3 77 Trigger GET Group Execute Trigger The f Trigger message causes the 3478A to initiate a measure ment cycle It is an HP IB Trigger and triggers the multimeter in any trigger mode since it has priority over the other trigger modes If the 3478A is triggered during a measurement cycle the cycle is aborted and a new cy cle is initiated There may be a delay up to 5 sec if a cycle is in progress when the trigger is received The multimeter has to be programmed to listen to execute the trigger 3 78 Clear DCL or SDC Device Clear or Selective Device Clear A Clear places the 3478A into its turn on routine
25. its The 5 1 2 4 1 2 and 3 1 2 digits can be selected by first pressing the blue Shift button and then either the AUTO MAN gt or lt gt button respectively 3 56 The Number Of Digits Displayed affects the reading rate of the multimeter This is because the number of digits determines the integration time of the A D Converter In the 4 1 2 digit mode the integration 3478A time is 1 60 second or 1 50 second for the 50Hz op tion which is called 1 PLC Power Line Cycle In the 3 1 2 digit mode the time is 1 600 second or 1 500 sec ond for the 50Hz option which is 1 PLC In the 5 1 2 digit mode the 3478A takes 10 readings using the 4 1 2 digit mode and averages them together for an extra digit of resolution This takes a time of 1 6 second or 1 5 second in the 50 Hz option which is 10 PLC For more information on run up time and the A D Converter refer to this manual s Section VII Service Group F A D Converter theory of operation 3 57 Autozero 3 58 The Autozero Function of the 3478A is used to compensate for offsets that may be present in the multimeter s internal circuitry DC Ohms Input Amplifier A D Converter etc The method used is to temporarily connect the input of the amplifier to ground the INPUT LO Terminal and make a measurement the INPUT HI Terminal is open at this time The off set reading is then stored into the 3478A s internal memory After that the short is removed and a
26. mV DC 300mV AC 300mA DC 300mA AC or most sensitive range on any other function 3V DC 3V AC 3A DC 3A AC or most sensitive range on any other function 30V DC 30V AC 30 Ohm or most sensitive range on any other func tion 300V DC 300V AC 300 Ohm or least sensitive range on any other function 3K Ohm or least sensitive range on any other function 30K Ohm or least sensitive range on any other function 300K Ohm or least sensitive range on any other function 3M Ohm or least sensitive range on any other function 30M Ohm or least sensitive range on any other function Autorange DIGITS DISPLAYED 3 1 2 Digits Displayed 4 1 2 Digits Displayed 5 1 2 Digits Displayed TRIGGER Internal Trigger External Trigger Single Trigger Hold Trigger Fast Trigger see paragraph 3 116 AUTOZERO Autozero Disabled Autozero Enabled DISPLAY Normal Display Operation Display Text and update Annun ciators Display Text and turn off Annun ciators HOME COMMAND Equivalent to F1T4R 2RAZ1N4 Equivalent to F1R 2RAZ1N4T3 Equivalent to F2R 2RAZ1N4T3 Equivalent to F3R 2RAZ1N4T3 Equivalent to F4R 2RAZ1N4T3 Equivalent to F5R 2RAZ1N4T3 Equivalent to F6R 2RAZ1N4T3 Equivalent to F7R 2RAZ1N4T3 MISC COMMANDS Read Status of the 3478A in Binary See paragrap
27. mple bits 0 and 5 are true which results in octal 41 the maximum value is 77 Refer to Table 3 7 byte 4 for the definitions of the bits The Error Register is also cleared by sending program code E 3 14 Table 3 7 Binary Status Byte Definition Bits Function Range and Number Of Digits True Displayed XXXXXX01 5 1 2 Digits Displayed XXXXXX10 4 1 2 Digits Displayed XXXXXX11 3 1 2 Digits Displayed XXX001XX 30mV DC 300mV AC 30 Ohm 300mA AC or DC or Extended Ohms Ranges XXXO010XX 300mV DC 3V AC 300 Ohm 3A AC or DC Ranges XXX011XX 3V DC 30V AC 3K Ohm Ranges XXX100XX 30V DC 300V AC 30K Ohm Ranges XXX101XX 300V DC 300K Ohm Ranges XXX110XX 3M Ohm Range XXX111XX 30M Ohm Range 001XXXXX DC Volts Function O10XXXXX AC Volts Function O11XXXXX 2 Wire Ohms Function 100XXXXX 4 Wire Ohms Function 101XXXXX DC Current Function 110XXXXX AC Current Function 111XXXXxX Extended Ohms Function Bit 1 Instrument Status Bits o Internal Trigger Enabled Autorange Enabled Autozero Enabled 3478A set for 50Hz Operation Front Rear Switch in Front Position Calibration RAM Enabled External Trigger Enabled Always Zero not true SRQ Mask Data Ready SRQ for every available reading to the HP IB Not used Syntax Error SRO if Syntax Error oc curs Internal Error SRO if Hardware Error occurs Front Panel SRQ SRQ if SRO button is pressed Calibra
28. n output after each trigger Function and range settings are selected from the front panel allel the pller ica om The ote eeds i ex is ad ress Ad IP 39 itch are of this nly sent the nal he ing P up ach 3478A Table 3 5 3478A Address Codes INSTRUMENT ADDRESS Shown at Factory Default Address 23 This number is called the Primary Address ASCII Code Character 5 bit Decimal Code OMNONNO AWN Q IT N lt XS lt CHVPIPVOZZTrA IONMIOHD 2 2 2 gt 0000000000000000 0000 2 0000 0000 0000 00 00 00 00 00 00 00 00 oo gt O0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 22 2 2 00000000 2 2 00O000000 3 98 3478A HP IB Programming 3 99 General The following paragraphs explain how to program the 3478A over the HP IB The information is given using the HP IB format rather than controller dependent language If the information is desired using controller dependent language refer to the 3478A s Operator s Manual 3 100 Programming the 3478A is done by DATA messages Set up information Range Function etc is DATA sent by the controller and is done using program codes The DATA received by the controller from the 3478A is measurement data and other data like the Status Byte and the five bytes from the Output Binary Status Byte 3 101 Program Codes All the program codes for the 3478A are listed in Table 3 6 T
29. n parallel with the input Measure the resistance first and then measure the unknown resistance The unknown resistance can then be calculated by this formula Ri Rt Rx Ri Rt where Rx is the unknown resistance Ri is the measured 10M ohm resistor and Rt is the measured value of the parallel combination 3 120 Reading the Binary Status Byte The current status or state of the 3478A can be determined by reading its Binary Status Byte The total number of bytes is five with each byte 8 bits wide The bytes can be read by sending program code B to the 3478A and then reading its output A small program to read the output using the hp Model 85 Personal Computer is as follows 10 OUTPUT 723 B 20 ENTER 723 USING 5 1B B1 B2 B3 B4 B5 The bytes are in variables Bl B2 B3 B4 and B5 The bytes and corresponding meanings of the bits when true are in Table 3 7 Program Code B clears the Er ror Register byte 4 see Table 3 7 3 121 Reading the Error Register Besides using Binary Status Byte 4 see previous paragraph the status of the Error Register can also be determined by sending pro gram code E to the 3478A and then reading its out put The output is a two digit octal number followed by a carriage return and line feed The number shows which bit s of the register is true a two digit number can be used since only 6 bits are used by the register For exa
30. ndependent of all other HP IB activity and is sent on a single line called the SRQ Line Its state is either true or false low true and high false The 3478A must be programmed to send the SRQ Message This is done by programming the SRQ Mask see paragraph 3 103 The front panel SRQ annunciator is on when the 3478A requires service 3 84 Since more than one device on the same Bus can output the SRQ Message the devices can be polled by the controller by a Serial Poll to determine if the 3478A or another device requires service The 3478A then outputs a Status Byte see paragraph 3 85 which shows for what reason the multimeter requires service 3 85 Status Byte The Status Byte is output by the 3478A in response to a Serial Poll The message has the same information as the 3478A s Status Register see next paragraph and sets the corresponding bit true for any true SRQ condition shown in Table 3 4 whether the SRQ Mask is set or not The bit is represented in Figure 3 6 3 86 The 3478A can require service if any condition in Table 3 4 is true Since the SRQ Mask must be set to output the Require Service Message except for bit 7 which is set by the Power On SRQ switch the 3478A s Status Register is used to monitor the conditions This way only the condition that is set by the mask outputs the SRQ Message Other true conditions that can cause an SRQ Message but which are not set by the SRQ Mask remain in the Status
31. on the range selected The readings can be displayed either as a 5 4 or 3 digit reading depending on the selected Number of Digits Displayed see paragraph 3 54 Refer to Table 1 1 or Table 4 1 for the DC Current Function s accuracy specifications NOTE Current inputs of greater than about 1 amp may cause the current shunt s 1 ohm Resistor value to change slightly due to self heating This may cause inaccuracies in the measurement Sufficient time should be allow ed for the circuitry to settle after the measure ment is complete and before other critical current measurements are made 3 34 AC Current Measurements 3 35 The 3478A can make ac current measurements from 1uA to 3A in two ranges 300mA and 3A The fre Operation quency response is from 20Hz to 20KHz The ranges are protected from excessive currents and voltage by a 3A fuse Select the AC Current Function to measure ac cur rents by pressing the a button 3 36 The AC Current Function is similar to the DC Current Function see paragraph 3 30 a voltage drop across a resistor is measured The difference is that the resultant ac voltage is changed from ac to dc using the AC to DC Converter Similar to the AC Volts Function all ranging is done in the converter 3 37 When the AC Current Function is selected the right side of the display shows MAAC or AAC dependent on the range selected The readings can be displayed either as a 5 1 2 4 1
32. owing lists the different 3478A remote operations a 3478A Response to Bus Messages paragraph 3 74 Title Paragraph Data 3 76 Trigger GET 3 77 Clear DCL or SDC 3 78 Remote 3 79 Local 3 80 Local Lockout 3 81 Clear Lockout and Set Local 3 82 Require Service SRQ 3 83 Status Byte 3 85 Status Bit 3 89 Pass Control 3 90 Abort 3 91 b 3478A Addressing paragraph 3 92 and Talk Only Mode paragraph 3 96 c 3478A HP IB Programming paragraph 3 98 Title Paragraph General 3 99 Program Codes 3 101 Programming the SRQ Mask 3 103 Clearing Status Register Status Byte 3 105 Power On SRQ 3 106 Sending Data to the Display 3 107 Home Commands 3 110 Reading Data from the 3478A 3 111 Front Rear Switch Position 3 113 Data Ready Feature 3 114 Front Panel SRQ 3 115 Fast Trigger 3 116 d Advanced Programming paragraph 3 117 Title Paragraph 3 118 3 119 General Extended Ohms Operation Reading the Binary Status Byte 3 120 Reading the Error Register 3 121 3 74 3478A Response to Bus Messages 3 75 The following paragraphs explain the 3478A s response to Bus Messages The multimeter s Bus capabilities are in Table 3 3 Table 3 3 3478A s Bus Capabilities Mnomonie Interface Function Name Source Handshake Capability Acceptor Handshake Capability Talker Basic Talker Serial poll Talk Only Mode Unaddressed to Talk if Addressed to Listen Listener Basic Listener Unaddressed to L
33. r 3 1 2 digit reading 478A he 3478A dependent on the selected Number Of Digits Displayed see paragraph 3 54 A 03 second or a 3 second delay is also applied before each reading in the 3M ohm and 30M ohm Ranges respectively Refer to Table 1 1 or Table 4 1 for the Ohms Function s accuracy specifica tions NOTE To insure 4 Wire Ohms accuracy when using long leads it is suggested to keep the lead resistance as follows 1 Ohms Sense Lead lt 10K ohms on all ranges 2 Ohms LO Source Lead lt 1 30 ohms of full scale on all ranges 3 Ohms HI Source Lead lt 1 30 ohms of full scale on the 3K through 30M ohm ranges and lt 3K ohms on the 30 and 300 ohms ranges 3 30 DC Current Measurements 3 31 The 3478A can make dc current measurements from luA to 3A in two ranges 300mA and 3A The ranges are protected from excessive currents and voltages by a 3A 250V fuse Select the DC Current Function to measure dc currents by pressing the A button 3 32 In the DC Current Function the current is ap plied between the INPUT LO and A Terminals Since a known value resistor 1 ohm is connected between the terminals a voltage proportional to the unknown cur rent and the resistor is generated This voltage is measured by the 3478A s dc circuitry Input Circuitry and A D Converter 3 33 When the DC Current Function is selected the right side of the display shows MADC or ADC dependent
34. regular input measurement is made The offset reading is then subtracted from the input reading and the compensated reading is displayed 3 59 The Autozero Function is enabled when the 3478A is turned on and after doing a Self Test see paragraph 3 60 The feature can be disabled by press ing the blue Shift button and then the INT TRIG but ton The AZ OFF annunciator on the display will light showing that the function is off After the func tion is turned off the multimeter immediately takes an offset reading and stores it into memory This last reading is then subtracted from the input measurements that follow Since no more offset readings are taken the reading rate of the 3478A is faster up to twice as fast If a range function or digit change is made or an at tempt is made to calibrate the 3478A a new offset reading is taken With Autozero off the 3478A s input circuitry remains in a static state This is useful when making measurements in extremely high impedance cir cuits where the internal switching transients of the 3478A may affect the reading accuracy NOTE The 3478A s long term stability may be af fected if the Autozero feature is disabled 3 60 Self Test Reset Operation 3 61 The 3478A uses an Internal Self Test to check its display and internal circuitry The multimeter goes through the test at turn on and also when the Self Test is selected The test can be selected by pressing the blue Shift b
35. s set an attempt to calibrate the 3478A has failed This is the SRQ bit This bit is true only if a Require Service Message is output Power On SRQ Shows that a power on reset has occurred See paragraph 3 106 Note More than one bit in the Status Byte can be true see paragraph 3 87 is output the Status Register s Data Ready bit is true The only way the SRQ Message is output is if the Front Panel SRQ condition is true 3 87 More than one bit in the Status Byte Message can be true For example bit 0 2 and 4 are true remember bit 6 is true for any SRQ condition if the SRQ Mask is set for the condition making the resultant Status Byte look like the following b7 bO oT TOP forty oft NOTE A 1 in this example shows a true condi tion 3 10 3478A 3 88 The byte is output as shown in the previous exam ple with the corresponding octal number of the example at 125 shown as follows 01 010 101 mm 3 89 Status Bit The 3478A does not respond to a Parallel Poll The Status Bit is used only for Parallel Poll and should not be confused with the bits in the Status Byte Message 3 90 Pass Control The 3478A does not have controller capabilities 3 91 Abort Interface Clear All HP IB communica tion is terminated including the 3478A s Bus com munication Control is returned to the controller The Abort Message does not remove the 3478A from remote control 3 92
36. see paragraph 3 7 In addition the multimeter s address switch see paragraph 3 92 is read and the SRQ Mask is set to zero or octal 200 if the Power On SRQ switch is on see paragraph 3 106 If during the turn on routine an error is detected the hard ware error bit in the serial poll register is set 3 79 Remote The Remote Message allows the 3478A to be controlled over the HP IB In remote the front panel buttons except the LOCAL and Front Panel SRQ but tons are disabled The Local and Front Panel SRQ but tons are only disabled when the 3478A is in remote and local lockout see paragraph 3 81 The instrument state in remote is determined by the local state before being placed in remote The RMT annunciator on the display will also be on with the 3478A in remote 3 80 Local This message clears the remote operation of the 3478A and enables its front panel operation Pressing the front panel LOCAL button also places the multimeter in the local state if the button has not been Operation disabled by the Local Lockout Message see next paragraph 3 81 Local Lockout All the front panel buttons are disabled with this message if the 3478A is in remote The message is in effect until cleared over the HP IB or power is cycled 3 82 Clear Lockout and Set Local This message plac ed the 3478A into local and the Local Lockout Message is cleared 3 83 Require Service SRQ The Require Service Message SRQ Message is i
37. ss the buttons again for the function s full scale calibration Refer to Sec tion IV of this manual for the calibration procedures NOTE The CAL ENABLE Switch on the front panel should not be in the CAL ENABLE position under normal use It should only be in that position to calibrate the instrument 3 66 MISCELLANEOUS OPERATIONS 3 67 Voltmeter Complete 3 68 The Voltmeter Complete connector is aBNC con nector which outputs a signal at the end of the A D cy cle The signal is a negative going TTL compatible pulse with a time period of approximately 14S The Voltmeter Complete connector is located on the rear panel 3 69 REMOTE OPERATION 3 70 General 3 71 The following paragraphs gives device dependent information necessary to remotely operate the 3478A over the Hewlett Packard Interface Bus HP IB Directions for mechanical interface connections to the HP IB are given in Section II of this manual Familiarize yourself with the front panel operation local before attempting to use the multimeter in remote HP IB NOTE HP IB is Hewlett Packard s implementation of IEEE Std 488 1978 Standard Digital Interface for Programmable Instrumenta tion and ANSI MC 1 1 3 72 A general description of the HP IB is in this manual s Appendix A Refer to the appendix for any non 3478A related HP IB information It is assumed in the following paragraphs that you are knowledgeable about the HP IB 3 73 The foll
38. tion Error SRQ if CAL pro cedure failed Always Zero not true Power On SRQ PON SRQ switch on last time power was turned on or DCL message was received Internal Error Information Set if any of the Calibration RAM loca tions have incorrect checksums or if a range with an incorrect checksum is selected The Main CPU RAM Self Test has failed The Control ROM Self Test has failed An A D Slope Error was detected The A D has failed its Internal Self Test A failure in the A D link between U403 and U462 Always Zero Always Zero A D DAC Value A decimal value between O to 63 represents the setting of the internal Digital to Analog Converter DAC Refer to this manual s Section VII for
39. tion is 4 Wire Ohms The corresponding program codes are F4R 2RAZINAT3 f HS Command DCI Same as the H1 com mand except the selected function is DC Current The corresponding program codes are F5SR 2RAZINAT3 g H6 Command ACI Same as the H1 com mand except the selected function is AC Current The corresponding program codes are F6R 2RAZINAT3 h H7 Command Ext Ohms Same as the H1 com mand except the selected function is Extended Ohms see paragraph 3 119 The corresponding program codes are F7R 2RAZIN4T3 3 111 Reading Data from the 3478A Data in the form of readings can be output by the 3478A over the HP IB other data that can be output is discussed in later paragraphs To output a reading if available the 3478A has to be addressed to talk The readings are output using 13 ASCII characters and are in the follow ing form Operation amp D DDDDDE D CR LF EON Polarity of reading a is sent for ac readings Reading expressed in scientific notation D is a decimal digit Carriage Return Line Feed with End or Identify Line set 3 112 Each character in the output statement except EOD is one byte which adds up to 13 The exponent will be in engineering notation E 3 E 0 E 3 or E 6 and the mantissa will always have 1 2 or 3 digits before the decimal point D DDDDD DD DDDD or DDD DDD If the 3478A is in th
40. utton and then the SGL TRIG button When the test is selected from the front panel all the segments of the display are on except are on as long as the test but ton is pressed After that SELF TEST will be Operation displayed during the time of the test When the test is completed SELF TEST OK will be displayed if the test passes The 3478A then resets to its turn on state see paragraph 3 9 not the previous state before the test was selected For 3478As with serial numbers 2301 A03760 and below or any instruments that have the Revision B ROM U502 installed the instrument turns on all the segments in the display for about five seconds The display then may show a certain message for about 1 4 second When the Self Test is completed the multimeter s displays its remote HP IB address for about one second The address is displayed as HPIB ADRS dd where dd is the address code of the instrument 3 62 If the Self Test fails an error message will be displayed indicating the type of failure If there are multiple failures only one failure will be displayed The 3478A then attempts to operate normally even if a test fails If another failure is noted while trying to operate normally the new failure will be displayed This con tinues until the test s passes or the instrument is taken out of the Self Test mode Table 3 2 3478A Error Messages Error Message Definition U C RAM FAIL The 3478A
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