Fluke 2680A Service Manual page 8

268XA
Service Manual
2 Theory of Operation........................................................................... 2-1
Introduction ....................................................................................................... 2-3
Main Power Supply....................................................................................... 2-5
Secondary Supplies ....................................................................................... 2-5
Out-Guard Overview..................................................................................... 2-5
Microprocessor ......................................................................................... 2-6
FPGA ........................................................................................................ 2-7
Other Bus Devices .................................................................................... 2-8
Serial Devices ........................................................................................... 2-9
Trigger In/Out, Master Alarm................................................................... 2-9
PCMCIA Interface PCA (2686A-4041) ............................................................ 2-10
Backplane PCA (268XA-4001)......................................................................... 2-10
Display Interface ........................................................................................... 2-11
Module Interface ........................................................................................... 2-11
Module Power Supply PCA (268XA-4031)...................................................... 2-11
Digital Input/Output PCA.................................................................................. 2-11
Microcontroller ............................................................................................. 2-12
Data Input Threshold..................................................................................... 2-12
Digital Input Buffers ..................................................................................... 2-13
Digital Output Drivers................................................................................... 2-13
Relay Output Drivers .................................................................................... 2-13
Totalizer Input............................................................................................... 2-14
Totalizer Enable ............................................................................................ 2-14
A/D Theory of Operations................................................................................. 2-14
A/D Converter PCA Block Description ........................................................ 2-14
Analog Measurement Processor ............................................................... 2-15
Input Protection......................................................................................... 2-15
Input Signal Conditioning......................................................................... 2-15
Analog-to-Digital (a/d) Converter ............................................................ 2-15
Inguard Microcontroller............................................................................ 2-15
Channel Selection ..................................................................................... 2-15
Open Thermocouple Check ...................................................................... 2-16
Analog Input PCA Block Description........................................................... 2-16
20-Channel Terminals............................................................................... 2-16
Reference Junction Temperature .............................................................. 2-16
A/D Converter PCA Circuit Description ...................................................... 2-16
Stallion Chip ............................................................................................. 2-18
Input Protection......................................................................................... 2-18
Input Signal Conditioning......................................................................... 2-18
Function Relays ........................................................................................ 2-18
Channel Selection Circuitry...................................................................... 2-19
DC Volts and Thermocouples Measurement Circuitry............................. 2-19
Ohms and RTD Measurement Circuitry ................................................... 2-20
AC Volts Measurement Circuitry. ............................................................ 2-22
Frequency Measurements ......................................................................... 2-23
Active Filter (ACV Filter) ........................................................................ 2-24
Voltage Reference Circuit ........................................................................ 2-24
Analog/Digital Converter Circuit ............................................................. 2-24
Autozero ................................................................................................... 2-24
Integrate .................................................................................................... 2-25
Deintegrate1.............................................................................................. 2-25
Deintegrate2.............................................................................................. 2-27
Overhead................................................................................................... 2-27
Inguard Digital Kernel Circuitry............................................................... 2-27
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