Resistance Measurement, Wire Ohms | Fluke 8842a manual

8842A

Instruction Manual

3.Allow the displayed reading to settle.

4.Press the OFFSET button.

5.Remove the resistor.

6.Proceed with the desired measurement.

Example:

Measure a 1.5V source with 1 MΩ source impedance, correcting for input bias current.

1.Connect a 1 MΩ resistor between the INPUT HI and INPUT LO terminals.

2.Select the VDC function and the 2V range.

3.Allow the display to settle.

4.Press OFFSET. (This zeroes the input bias current error.)

5.Remove the 1 MΩ resistor.

6.Measure the voltage of the circuit under test.

Note that this procedure does not correct for circuit loading error. Also note that if input bias current error is not corrected for, it may be added to the circuit loading error.

4-5. RESISTANCE MEASUREMENT

The 8842A allows you to measure resistance in both 2-wire and 4-wire configurations. Each has its benefits.

4-6. 2-Wire Ohms

Two-Wire ohms measurements are simple to set up and yield good results for most measurement conditions. Measurements are made as shown in Figure 4-3. An internal current source (the "ohms current source") passes a known test current (Itest) through the resistance being tested (Runknown). The 8842A measures the voltage drop across Runknown, calculates Runknown using Ohm’s law (Runknown = Vtest/Itest), and displays the result.

f4-03.wmf

Figure 4-3. Wire Ohms Measurement

4-4

Image 95

Fluke 8842a instruction manual Resistance Measurement, Wire Ohms

Contents

8842A Page Table of Contents Remote Programming 8842A Measurement Tutorial Maintenance List of Replaceable Parts Schematic Diagrams List of Tables 805-7 List of Figures 805-8 IEEE-488 Interface PCA, Option True RMS AC PCA, Option Xii Introduction and Specifications 8842A Digital Multimeter Options and AccessoriesIntroduction Specifications True RMS AC Voltage Option 8842A-09 Peak NM SignalRate Filter For Inputs FrequencyFundamental Frequency Crest Factor ½ Digits CurrentFull Scale 5½ Digits Through Unknown Range Full Scale Resolution Current ½ Digits Hours 23±1C Function Rate Power Line FREQUECNCY1Automatic Settling Time Delay Autoranging Conversion Time ms 50 Hz 60 Hz 400 Hz External Trigger Timing Characteristics General Power Operating Instructions Connecting to Line Power InstallationInstalling the Power-Line Fuse Rack Mounting Kits Adjusting the Handle Front and Rear Panel Features Operating FeaturesPower-Up Features Operating Features Local button causes the 8842A to display its Rear Panel Features Error Messages Display Features Meaning Error Code Error Code Autorange Diagnostic Self-TestsOverrange Indication Ranging Triggering Continuous Trigger ModeExternal Trigger Mode Manual Range Sample Complete Output Option -05 Only Automatic Settling Time DelayExternal Trigger Input Option -05 Only Measuring Current Making MeasurementsInput Overload Protection Limits Measuring Voltage and Resistance Offset Measurements Measuring Voltage and Resistance External Cleaning 8842A Remote Programming Measurement Data Overrange Indication Error Messages Capabilities BUS SET-UP Procedure IEEE-488 Address Selection AN Overview of Remote Operation AN Overview of Remote Operation ExampleExplanation DEVICE-DEPENDENT Command SET DEVICE-DEPENDENT Command SET Device-Dependent Command Set Dn Display Commands Bn Offset CommandsCn Calibration Commands Get Commands Fn Function Commands Meaning Command Output String 14. G2 Get Calibration Prompt 12. G0 Get Instrument Configuration13. G1 Get SRQ Mask 16. G4 Get Calibration Status 15. G3 Get User-Defined Message 18. G6 Get YW Status 19. G7 Get Error Status17. G5 Get IAB Status 20. G8 Get Instrument Identification Numeric Entry CommandPut Commands 23. P0 Put Instrument Configuration 25. P2 Put Calibration Value 24. P1 Put SRQ Mask 26. P3 Put User-Defined Message Rn Range CommandsSn Reading Rate Commands Trigger Selection Logic Diagram Tn Trigger Mode Commands 33. Z0 Self-Test Command Wn Terminator Commands31. X0 Clear Error Register Command Yn Suffix Commands Input Syntax Device-Clear Command35. ? Single-Trigger Command Input Processing Definitions Interface Messages ERROR-PRODUCING CharactersDEVICE-DEPENDENT Messages Incorrect example Syntax Rules Loading Output Data Output Data Measurement Data Numeric Data and Error MessagesOverrange Indication Error Messages Types of Output Data Output Priority Error MessagesOverrange Indication Status Data Serial Poll Register Service Requests Set SRQ Mask Address Messages Universal CommandsInterface Messages Addressed Commands TALK-ONLY Mode Timing Considerations Immediate Mode CommandsRemote Calibration Example Programs Immediate-Mode Commands for Various Controllers Example Programs 10. Example Program Taking Readings with Local Control 11. Example Program Using the Serial Poll Register 12. Example Program Record Errors During Selftest 13. Example Programs Using the IBM PC 14. Example Programs Using the IBM PC F3-1402.wmf F3-1403.wmf F3-1404.wmf F3-1405.wmf F3-1406.wmf F3-1407.wmf F3-1408.wmf F3-1409.wmf F3-1410.wmf F3-1411.wmf ASCII/IEEE Std 488-1978 Bus Codes 8842A Measurement Tutorial DC Voltage Measurement Circuit Loading Error Measuring Input Bias Current Error Input Bias Current Error Resistance Measurement Wire Ohms Correcting for Test Lead Resistance in 2-Wire Ohms Full Scale Voltage Test Current Applications of the Ohms Functions Testing DiodesTesting Electrolytic Capacitors Precision Current Source DC Current Measurement Reducing Thermal Voltages Burden Voltage Error Calculation Waveform Comparison AC Voltage and Current MeasurementTrue RMS Measurement AC Voltage and Current Measurement AC-Coupled AC Measurements Crest Factor Bandwidth Zero-Input VAC ErrorCombined AC and DC Measurements 20Ω Ranges Reduction of Zero-Input Error 10. Shielding for Low Voltage Measurements Making Accurate HIGH-RESISTANCE Measurements 12. Leakage Resistance in High Resistance Measurement Theory of Operation True RMS AC Option VAC Scaling MA AC Scaling Overall Functional Description DC Scaling Detailed Circuit Description DC Scaling DC Scaling VDC and mA DC VDC Scaling Analog Filter VDC ProtectionMA DC Scaling Track/Hold Amplifier TRACK/HOLD Circuit TRACK/HOLD Circuit Timing Diagram for One A/D Cycle Track Configuration Precision Voltage Reference Settling ConfigurationHold Configuration Pre-Charge Configuration Ohms Current Source Ohms Current Source Ohms Functions Ohms Protection Ohms Scaling 20. A/D Converter Analog-to-Digital Converter Precision DAC Timing/Data Control 23. A/D Amplifier Bootstrap SuppliesDisplay Digital Controller Keyboard 13. Digital Controller Block Diagram In-Guard Microcomputer 14. Read/Write Timing Diagrams for Internal Bus Calibration Correction Slow Medium Fast Power Line FrequencyFunction and Range Control 30. A/D Control and Computation Guard-Crossing Communication Troubleshooting ModesGuard Crossing Keyboard/Display Control Power Supply Bus Interface Circuitry IEEE-488 Interface OptionOut-Guard Microcomputer Guard Crossing VAC Scaling Signal ConditioningIEEE-488 Interface Power Supply True RMS AC-to-DC Conversion MA AC ScalingFrequency Response Trimming Static awareness Dow Chemical Maintenance External Trigger Polarity Selection Option -05 Only Instrument Type Minimum Specifications Recommended Model Frequency Range Minimum Required Accuracy All Ranges Performance Test DC Voltage Test Slow Medium Fast MIN MAX Step Range Input Voltage Frequency AC Voltage Test Option -09 Only New Offset must be stored for each new range selected Resistance Test Fast MIN MAX DC Current TestDisplayed Reading Slow Medium MIN MAX Input Current Frequency CalibrationAC Current Test Option -09 Only Step Number Range Initial Procedure Basic Calibration Procedure Calibration Functions 12. A/D Calibration Step Input L O W a B L E ErrorStep Displayed Prompt Displayed Prompt VDC VAC1 Offset and Gain CalibrationStep HIGH-FREQUENCY AC Calibration Step Displayed PROMPT1,2 Advanced Features and Special ConsiderationsStoring Variable Inputs Verifying Calibration Procedure Function LOW Prompt High PromptCalibrating Individual Ranges Tolerance Check Erasing Calibration Memory Tolerance AC Calibration AT Other FrequenciesOptimizing USE of the 5450A Calibration Optimizing Use of the 5450A Remote Calibration Comments Front Panel FeatureCorresponding Command 8842A Timing Considerations Example Calibration Program Remote Erasure Example A/D Calibration Program Disassembly Procedure Case Removal A Disassembly F6-062.wmf F6-063.wmf F6-064.wmf Main PCA Removal True RMS AC PCA Removal Option -09 OnlyIEEE-488 Interface PCA Removal Option -05 Only Maintenance Front Panel Disassembly Reassembly Procedure Reassembly Procedure Front Panel Disassembly Removing the Display Window Initial Troubleshooting Procedure Internal Fuse ReplacementTroubleshooting Troubleshooting 16. Overall State Table T6-162.wmf 17. Circuitry Tested by the Analog Self-Tests Diagnostic Self-Tests Test Point Voltage Self-Test DescriptionsTest Number Maintenance 8842A IN-GUARD Microcomputer System Digital Controller Troubleshooting In-Guard Microcomputer Address Latch U219 Display System Calibration Memory U220 Display Control U212 To-8 Strobe Decoder U213 Analog Control Signals Device REF. DES Evaluating Static Signals 21. Analog Control Logic States DC Scaling Troubleshooting Evaluating Dynamic Signals Supply Voltage PIN or Device Ohms Current Source Troubleshooting Track/Hold Troubleshooting 13. Typical Output Waveforms for Track/Hold Circuit TP103 Precision Voltage Reference Troubleshooting 14. Output of A/D Amplifier TP101 66. A/D Converter Troubleshooting 15. Waveforms at U101-24 and U101-25 For fire protection, use exact fuse replacement only Power Supply Troubleshooting 17. Waveforms at TP102 for Several Inputs on 2V DV Range Minimum Maximum Test Point Diagnostic Program IEEE-488 Interface Troubleshooting OptionService Position Switches Configuration Troubleshooting Port BIT True RMS AC Troubleshooting Option Defective Stage Major ProblemsDefective Ranges Voltage AT TP802 Input VoltageVoltage AT TP801 More Obscure Problems Cleaning Printed Circuit Assemblies Internal CleaningGuard Crossing Troubleshooting 21. Guard Crossing Test Waveforms Cleaning After Soldering 8842A List of Replaceable Parts 8842A Manual Status Information HOW to Obtain Parts Newer Instruments Service Centers Revision Level Assembly Fluke Part noREF of Option no F7-011.wmf F7-012.wmf F7-013.wmf F7-014.wmf A1 Main PCA CABLE, Display HEADER,1 ROW,.156CTR,6 PIN 8842A F7-03.wmf A2 Display PCA F7-03.wmf Supply Codes for Manufacturers Supply2.wmf Service Centers Service2.wmf 8842A Options and Accessories 8842A Number Option ModelDescription Accessories High Voltage Probes 80K-6 and 80K-40 Current Shunt 80J-10Current Probes Y8100, Y8101, 80i-400 8842A Option -05 IEEE-488 Interface 805-2 External Controls List of Replaceable Parts MaintenanceProgramming Instructions List of Replaceable Parts 805-6 805-7 805-8 Option -09 True RMS AC 809-2 Option -09 True RMS AC Operating Instructions 809-5 Option -09 True RMS AC PCA 809-7 809-8 Schematic Diagrams 8842A Schematic Diagrams F9-012.wmf Main PCA, A/D Converter F9-022.wmf Main PCA, Ohms Current Source F9-032.wmf Main PCA, Digital F9-042.wmf Main PCA, Power Supply F9-052.wmf Display PCA F9-062.wmf F9-071.wmf F9-072.wmf IEEE-488 Interface PCA, Option IEEE-488 Interface PCA, Option -08