MA AC Scaling, Frequency Response Trimming | Fluke 8842a manual

8842A

Instruction Manual

U806A, U806B, and a voltage divider (R804 and R805) provide gain which is selected for each range by the analog switches in U804. The configuration for each range is shown in Figure 5-17. (In this figure, the CMOS analog switches are represented by mechanical switches.) When U806A is not used, its non-inverting input is grounded by Q804. When U806B is not used, its non-inverting input is connected to the CURRENT SENSE line.

5-45. mA AC Scaling

The mA AC function uses the same current shunt and protection network which is used for dc current. In the mA AC function, Q802 switches the CURRENT SENSE line to the non-inverting input of U806B, which provides a gain of 10.

5-46. Frequency Response Trimming

The frequency response is trimmed by software calibration using a digitally controlled one-pole low-pass filter (R832 and a combination of C826, C827, C828, and C829). The analog switches in U808 configure the four capacitors to select one of 16 possible RC constants. The input of the digitally controlled filter is buffered by voltage follower U801A. The individual gain stages are also provided with fixed frequency compensation.

5-47. True RMS AC-to-DC Conversion

U801B buffers the input to rms converter U802. U802 computes the rms value of the scaled input voltage as shown in Figure 5-18. Rather than explicitly squaring and averaging the input, U802 uses an implicit method in which feedback is used to perform an equivalent analog computation.

f5-18.wmf

Figure 5-18. True RMS AC-to-DC Converter

The filter averages the divider output signal. This filter consists of U809A, C813, R815, and the internal 25 kΩ resistor and op amp between pins 8 and 9 of U802. The output is further filtered by a three-pole post-filter comprised of U809B and associated resistors and capacitors. This output is then switched into the Track/Hold Amplifier of the dc front end via U302 pins 15 and 14. The Track/Hold Amplifier is set up for unity gain on all ac ranges.

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Fluke 8842a instruction manual MA AC Scaling, Frequency Response Trimming, True RMS AC-to-DC Conversion

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 Options and Accessories Introduction8842A Digital Multimeter Specifications True RMS AC Voltage Option 8842A-09 Peak NM SignalRate Filter For Inputs FrequencyFundamental Frequency Crest Factor Current Full Scale 5½ Digits½ 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 Installation Installing the Power-Line FuseConnecting to Line Power Rack Mounting Kits Adjusting the Handle Operating Features Power-Up FeaturesFront and Rear Panel 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 Automatic Settling Time Delay External Trigger Input Option -05 OnlySample Complete Output 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 Bn Offset Commands Cn Calibration CommandsDn Display Commands Get Commands Fn Function Commands Meaning Command Output String 12. G0 Get Instrument Configuration 13. G1 Get SRQ Mask14. G2 Get Calibration Prompt 16. G4 Get Calibration Status 15. G3 Get User-Defined Message 19. G7 Get Error Status 17. G5 Get IAB Status18. G6 Get YW 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 Rn Range Commands Sn Reading Rate Commands26. P3 Put User-Defined Message Trigger Selection Logic Diagram Tn Trigger Mode Commands 33. Z0 Self-Test Command Wn Terminator Commands31. X0 Clear Error Register Command Yn Suffix Commands Device-Clear Command 35. ? Single-Trigger CommandInput Syntax Input Processing Definitions ERROR-PRODUCING Characters DEVICE-DEPENDENT MessagesInterface 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 Universal Commands Interface MessagesAddress Messages Addressed Commands TALK-ONLY Mode Immediate Mode Commands Remote CalibrationTiming Considerations 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 Testing Diodes Testing Electrolytic CapacitorsApplications of the Ohms Functions Precision Current Source DC Current Measurement Reducing Thermal Voltages Burden Voltage Error Calculation AC Voltage and Current Measurement True RMS MeasurementWaveform Comparison AC Voltage and Current Measurement AC-Coupled AC Measurements Crest Factor Zero-Input VAC Error Combined AC and DC MeasurementsBandwidth 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 VDC Protection MA DC ScalingAnalog Filter 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 Bootstrap Supplies Display23. A/D Amplifier 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 Signal Conditioning IEEE-488 Interface Power SupplyVAC Scaling MA AC Scaling Frequency Response TrimmingTrue RMS AC-to-DC Conversion 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 L O W a B L E Error Step Displayed PromptStep Input Offset and Gain Calibration StepDisplayed Prompt VDC VAC1 HIGH-FREQUENCY AC Calibration Advanced Features and Special Considerations Storing Variable InputsStep Displayed PROMPT1,2 Procedure Function LOW Prompt High Prompt Calibrating Individual RangesVerifying Calibration Tolerance Check Erasing Calibration Memory Tolerance AC Calibration AT Other FrequenciesOptimizing USE of the 5450A Calibration Optimizing Use of the 5450A Remote Calibration Front Panel Feature Corresponding CommandComments 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 True RMS AC PCA Removal Option -09 Only IEEE-488 Interface PCA Removal Option -05 OnlyMain PCA Removal Maintenance Front Panel Disassembly Reassembly Procedure Reassembly Procedure Front Panel Disassembly Removing the Display Window Internal Fuse Replacement TroubleshootingInitial Troubleshooting Procedure Troubleshooting 16. Overall State Table T6-162.wmf 17. Circuitry Tested by the Analog Self-Tests Diagnostic Self-Tests Self-Test Descriptions Test NumberTest Point Voltage 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 IEEE-488 Interface Troubleshooting Option Service PositionDiagnostic Program Switches Configuration Troubleshooting Port BIT True RMS AC Troubleshooting Option Major Problems Defective RangesDefective Stage Input Voltage Voltage AT TP801Voltage AT TP802 More Obscure Problems Internal Cleaning Guard Crossing TroubleshootingCleaning Printed Circuit Assemblies 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 Assembly Fluke Part no REF of Option noRevision Level 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 Model DescriptionNumber Option Accessories Current Shunt 80J-10 Current Probes Y8100, Y8101, 80i-400High Voltage Probes 80K-6 and 80K-40 8842A Option -05 IEEE-488 Interface 805-2 External Controls Maintenance Programming InstructionsList of Replaceable Parts 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