Allen-Bradley ClutchBrake PLC-5 Series - Troubleshooting with Snapshot Status Bits

Troubleshooting with Fault Codes, Operator Prompts, and Snapshot Status Bits C–9
Publication 65566.5.1 - October 1996
The primary means of troubleshooting the clutch/brake control
system is by means of reading fault codes and operator prompts as
presented earlier in this appendix or in the Operator’s Guide,
publication 6556-6.9.1 for PLC processors.
We present the following troubleshooting strategy as an alternative.
Whenever the processors turn off outputs to the main clutch/brake valves
such as due to detecting a fault, the control program takes a snapshot of
the bit logic controlling the press the instant the outputs are turned off.
You can use this information to troubleshoot the cause of the shutdown.
Do this by comparing the status of the snapshot bits with what the status
should have been according to your ladder logic. Start at the last rung
controlling main valve outputs and work backwards until you find all
discrepancies.
The snapshot status of bit logic is stored in file N167:21 as follows:
(The processor substitutes actual status for illustrated bit status 0000.)
Realtime Storage 15 Snapshot Status 0
N168:
0
N167:
0
0000 0000 0000 0000
1 1
0000 0000 0000 0000
2 2
0000 0000 0000 0000
:
:
:
:
9 9
0000 0000 0000 0000
N160:
0 10
0000 0000 0000 0000
1 11
0000 0000 0000 0000
2 12
0000 0000 0000 0000
:
:
:
:
19 29
0000 0000 0000 0000
20 30
0000 0000 0000 0000
21 31
0000 0000 0000 0000
Troubleshooting with
Snapshot Status Bits