Troubleshooting Your Input Modules; Input Circuit Operation - Allen-Bradley SLC 500 User Manual

Troubleshooting Your Input
Modules
Allen-Bradley PLCs
The following will assist you in troubleshooting your input modules.

Input Circuit Operation

An input circuit responds to an input signal in the following manner:
1. An input filter removes false signals due to contact bounce or
electrical interference.
2. Opto-electrical isolation protects the input circuit and backplane
circuits by isolating logic circuits from input signals.
3. Logic circuits process the signal.
4. An input LED turns on or off indicating the status of the
corresponding input device.
Input
Input
Conditioning
Opto-Electrical
Logic
Isolation
Circuits
Publication 1747-UM011C-EN-P - December 2001
Troubleshooting 10-19
Backplane
LED