Runnable simulator field guide
Pump alternation PLC scenario: test checklist
Direct answer
The learner can explain when duty changes, prove that only eligible equipment is selected and recover from a failed lead without losing demand control.
Written for pLC and process learners implementing lead rotation for two pumps with demand, availability, run proof, failover, minimum timing, alarms and manual controls.
Scenario setup
Process demand, start and stop thresholds, hysteresis, duty state, alternation trigger, pump availability, command, run and flow proof, minimum on and off time, failover, alarm, manual mode and restart.
I/O and state map
Level, pressure or schedule demand through hysteresis and duty selection to pump command, starter or drive response, run and flow feedback, process change, alarm and next-duty memory.
Normal run
Successive completed demand cycles alternate available pumps while each start obtains proof and each stop returns to a known state.
Boundary run
Failed duty, unavailable standby, simultaneous demand, sensor chatter, no-flow proof, short cycling, manual override, alarm reset and power return.
Injected fault
A demand, threshold, duty-memory, availability, selection, command, starter, pump, feedback, process, alarm or restart mismatch.
Target check
The sequence verified with target PLC, actual hydraulic system, equipment constraints, protection and approved operating and functional-test procedures.
How do you alternate two pumps with a PLC?
Retain a duty state, change it at a declared event such as successful cycle completion, skip unavailable equipment and require command and process proof.
What happens if the duty pump fails?
A defined sequence should remove or alarm the failed command, confirm standby eligibility, start the standby when permitted and preserve evidence of the initiating failure.