Runnable simulator field guide
TON delay-on PLC scenario: test checklist
Direct answer
The learner can predict the timer state before, at and after the preset and explain what happens when the enabling condition changes.
Written for pLC beginners learning enable, elapsed time, done state, reset and scan effects through one observable delay-on task.
Scenario setup
Target timer semantics, enabling condition, instance, preset and units, accumulated or elapsed value, done output, reset condition, task period, output use and initial state.
I/O and state map
Input transition through rung truth, timer instance update, elapsed comparison, done state, downstream command and visible process response.
Normal run
Enable held long enough to reach the preset once, command the expected output and reset cleanly when false.
Boundary run
Just below preset, exact preset, one scan above, brief dropout, repeated enable, task-period change, skipped call, reset and power return.
Injected fault
An enable, instance, time-base, scan, comparison, reset, downstream-owner or restart mismatch.
Target check
The case repeated in the exact target timer instruction and task with measured elapsed behavior.
What does a TON timer do in a PLC?
A delay-on timer measures how long its enabling condition remains true and asserts its completion state according to the target-specific preset and execution rules.
Does a TON keep timing when its rung goes false?
A conventional nonretentive TON resets when disabled, but exact accumulator and status semantics must be checked on the selected platform.