PLC / PLC Programming, Timing & State Logic
Diagnose a PLC one-shot that never triggers or triggers unexpectedly
An edge detector depends on its input history and instance lifecycle. Reinitializing or conditionally calling it can change behavior.
Environment and inputs: Industrial PLC / automation guidance · Verify the exact controller, module, firmware, engineering tool and machine documentation. Linked vendor examples apply to their stated products and library versions; observation, state changes and physical work require distinct authorization.
Observe and record
Observe the source signal, detector call context, instance ownership and resulting pulse using supported monitoring without writing values.
Interpret the evidence
A one-cycle output is relative to the calling task, not necessarily visible at a slower HMI refresh. Different library blocks have documented startup semantics.
Resolve and verify
Use the matching library definition and test transitions, startup and reset cases in an offline or controlled environment before deployment.
Machine and data safeguards
Do not use a sampled HMI button as a substitute for required high-speed or safety-related event capture.