Runnable simulator field guide
Level-alarm stack PLC scenario: test checklist
Direct answer
The learner can apply stable thresholds, preserve first useful evidence, silence annunciation without hiding active alarms and reset only from permitted conditions.
Written for pLC and process-control learners building high-high, high, low and low-low alarms with distinct active, latched, acknowledged and shutdown behavior.
Scenario setup
Scaled level and quality, four thresholds, hysteresis, delay, active state, latch, priority, horn, lamp, acknowledgement, shutdown and reset permissive.
I/O and state map
Level signal through scaling and quality, alarm evaluation, retained state, annunciation, operator action, protective request and return-to-normal evidence.
Normal run
Each boundary enters and leaves predictably, higher priority is visible, acknowledgement silences without clearing and reset requires normal process state.
Boundary run
Rapid level movement, noisy threshold, bad quality, simultaneous alarms, acknowledge during active state, reset while active, restart, stale display and new alarm after acknowledge.
Injected fault
A signal, scale, quality, threshold, timer, latch, priority, acknowledge, output, shutdown or reset mismatch.
Target check
The design reviewed against the approved alarm philosophy, process limits, human-factors needs and independent protective layers.
How should high-high and high level alarms differ?
They should have distinct purposes, thresholds, priorities and responses; high-high may request protective action, while high provides earlier operator response time.
Should acknowledgement clear a level alarm?
No. Acknowledgement records operator recognition and may silence the horn. Active or latched indication should follow the declared return-to-normal and reset rules.