CCST 24 — Safety Category Levels

Briefing

Write a dual-channel E-stop circuit: two NC contacts ESTOP_CH1 and ESTOP_CH2 must BOTH be open to drop the output (Category 3 / PLd pattern). A discrepancy latch CHANNEL_FAULT fires if one is open but not the other.

Objectives

• SAFE_OUTPUT requires both channels to be de-energised to shut down
• CHANNEL_FAULT latches if CH1 ≠ CH2 for more than one scan
• Normal run: SAFE_OUTPUT := NOT ESTOP_CH1 AND NOT ESTOP_CH2 (both NC: both TRUE at rest means safe)

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Safe when both NC contacts closed

   Safe when both NC contacts closed

2. #2Both trip drops output

   Both trip drops output

3. #3One channel discrepancy flags fault

   One channel discrepancy flags fault