Detailed Circuit Description, DC Scaling | Fluke 8842a instruction

8842A

Instruction Manual

5-3. DETAILED CIRCUIT DESCRIPTION

The following paragraphs give a detailed circuit description of each of the functional blocks in Figure 5-1. For clarity, measurement ranges are referred to as r1, r2, r3, etc., where r1 is the lowest possible range, r2 the next higher range, and so on. Pins are designated by the respective integrated circuit (e.g., U101-7 for U101 pin 7).

5-4. DC SCALING

The DC Scaling circuit scales all in-range dc inputs so that the output of the Track/Hold (T/H) amplifier (U307) is within +/-2V. In addition, the DC Scaling circuit provides input protection and analog filtering. Additional scaling is provided by the the T/H Amplifier.

The following paragraphs describe the configuration of the DC Scaling circuit in the DCV and mA DC functions and also describe the analog filter. The ohms functions are described under a later heading because the T/H Amplifier provides additional input switching for these functions.

5-4

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Fluke 8842a instruction manual Detailed Circuit Description, DC Scaling

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