Chapter Eleven: Troubleshooting The Dia
nostics Feature
299
Code 7x: Response Time for Fail-Safe Feature
The x in the code represents the Auxiliary Output board relay letter (C or D).
Relays C and D on the Auxiliary Output board are associated with the 146 instrument’s Fail-Safe
feature. When the 146 unit is powered on, the Fail-Safe feature is activated. When Code 7x is
used, the processor sends a relay setup command to relays C, D, and then checks to see if the
relays have responded. If the relays do not respond, the abbreviation
Err
(for Error), appears
in the main display. If the relays do respond, the Fail-Safe feature continues, and the Code 7x
function determines the Fail-Safe system response time.
The Fail-Safe feature includes a timed hardware reset. The hardware reset causes relays C and D
to go to default positions. During normal operation of the 146 unit, the processor prevents the
timed hardware reset from executing by sending out an interrupt pulse every 10 milliseconds. If
the 146 unit’s software crashes, the interrupt pulse stops and the timed hardware reset executes,
causing relays C and D to go to default positions.
Code 7x is used to determine if the Fail-Safe system is operating, and its response time. The
response time is the amount of time which passes between when an interrupt pulse is received by
the hardware reset, and when relays C and D can be set to default. The response time should be
about 12 msec. ± 1 msec.
1. Press the [7/a] key, followed by either [9/
C
] (for Relay C), or [0/
D
] (for Relay D).
The system responds by displaying the Fail-Safe feature response time in milliseconds.
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