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CPU – The micro-controller processes the data received by the ADC’s and sends
a ohms reading to the display. Also from the data received from the keypad, the
micro-controller selects the current range, activates the LEDs and sends data out
from the rs-232 port.
Current Range Selector – The current range selection occurs within the micro-
controller. According to the data received from the keypad, a signal is sent to
activate the appropriate relay on the current source circuitry.
RS-232 – The RS-232 data is also sent and received by the micro-controller.
Display
– This is the visual interface to the user. The display receives its data directly
from the micro-controller.
Keypad Board (4176-701)
– This section of the ohmmeter contains the keypad and the
LED indicators for the TCM and HLC function.
Keypad – The keypad is used to send commands to the micro controller.
HLC LEDs – These LEDs indicate the result of the HLC comparison.
TCM LEDs – These LEDs indicate the status of the temperature compensation
mode.
10.4 Troubleshooting
Use the following guidelines to determine in which circuitry that fault originates:
•
If the fault occurs on one range only then the fault is probably in the current
source section. Connect the source binding post to an ammeter that can measure
up to 1Amp and has a resolution of at least 1
µ
A. Switch through the ranges and
check the value of the test current. If any given range does not output current,
check the relay for that specific range, or check if one of the range resistors is
open. If the value of the test current is outside of the specified tolerance, check
the potentiometer for that specific range.
•
If the fault is display related (e.g., missing segments, non-numeric data, etc.), the
first thing to do is reboot the instrument. If the problem persists, most likely the
fault can be traced to the display it self, the display cable or the micro-controller
board.
•
If the fault occurs on all ranges, you should verify that the micro-controller’s
ADC is working correctly. Select the 20m
Ω
range and apply 10mV to the sense
terminal. The display should read 10.000m
Ω
. Select the 100m
Ω
range and apply
