Fluke Biomedical 945A - Manual (Page 34)

Auto Zero Failure
If the preamplifier zero offset correction is near its limit, the preamplifier notifies the UDR. Error code
E0012 is displayed. The zero offset correction is related to the value of the auto zero counter which can
be displayed by setting the FUNCTION switch to position 8. A value of 0 to 255 is possible. A value that
is significantly different from 128 indicates that an auto zero adjustment on the electrometer board, in the
preamplifier, is needed.
High Voltage Failure
The preamplifier checks the ion chamber integrity approximately every four (4) minutes by pulsing the
high voltage and checking the response. This operation has no effect on the dose rate reported to the
UDR. If the integrity test fails, the failure is reported to the UDR, and the UDR will display E0011.
This failure generally indicates a loss of continuity in the ion chamber or bad connections between the ion
chamber and the preamplifier (cable failure). This failure will also occur if the high voltage drops to a
level such that 100% collection at full scale cannot be achieved by the ion chamber. If the detector is
disconnected for the purpose of inputting a test signal into the electrometer, the high voltage failure will
be detected. To prevent an unwanted FAIL alarm, during testing, the Maintenance Mode previously
described should be used.
Loop Failure
If the UDR does not receive a valid message from the preamplifier in ten seconds, a loop failure is
detected and an E0007 code is displayed.
The loop failure can originate from bad seating of the serial communications board in the UDR, bad
connections in the preamplifier, bad connections at the P2 connector of the UDR, a baud rate mismatch
between the setting on the serial board and that in the preamplifier, an invalid address setting on the
serial board, or blown loop fuses.
The baud rate of the preamplifier can be set to 300 or 4800 baud. SW3-1 on the 977 interface board
selects 300 when in the OFF position and 4800 in the ON position. 4800 baud is the normal factory
setting. The address of the serial board must be set 4040. If the wiring of the serial option board to the
P2 connector is suspected, a loop test can be performed as described in "Loop Test Mode". The
instruction manual for the communications loop option board (P/N 942-200-80-1) contains details on how
to set up the serial board in the UDR.
Power Failure
If power is lost to the UDR, the bargraph, alarm indicators, and the display are blanked (turned off). The
HIGH, WARN, and FAIL relay coils de-energize.
MPU Failure
If the fail timer circuit, which monitors the MPU function, is allowed to time out (because of a hardware
failure), a failure condition will be true.
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