Pro
12 min
CCST 19 — Diagnose: Intermittent Output Fault
ccstdiagnosticsintermittentscan
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Briefing
A pump output flickers intermittently. Root cause: an internal BOOL BIT_NOISE is being read before it is written each scan. Rewrite the logic to compute PUMP deterministically in a single rung.
Objectives
- Identify the scan-order dependency causing BIT_NOISE to be stale
- Rewrite to compute PUMP directly from sensor inputs without an intermediate bit
- Verify PUMP is stable
Hints
- Compute PUMP directly: PUMP := FLOAT_SWITCH AND NOT HIGH_LIMIT
- Avoid reading a bit that is written LATER in the scan
I/O Table
Inputs
FLOAT_SWITCHFloat switch (water present)
BOOL · %I0.0
HIGH_LIMITHigh-level limit switch
BOOL · %I0.1
Outputs
PUMPPump output
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1Pump on when float and not high
Pump on when float and not high
- #2Pump off at high limit
Pump off at high limit
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