Industrial Engineer · phase 6 of 16
Discrepancy Time
Maximum allowed time difference between the expected state changes of paired safety channels.
The Explain card
- Plain English
- Discrepancy time is how long two channels of a safety input are allowed to disagree before the controller calls it a fault. It exists because two real contacts never change at exactly the same instant.
- Example
- A door switch's channels are set to a 50 millisecond discrepancy. One contact opens, the other follows 8 milliseconds later, and the input is treated as a clean open. If the second one never follows, the input faults.
- Why it matters
- Too short and healthy switches fault on every slow actuation, too long and a real wiring failure hides for that long. The value is a judgement about the device, and the vendor's number is the place to start.
- Hook
- How long the two witnesses may argue.
Where it sits in the deck
Phase 6: PLC Operating Modes, Safety, and Diagnostics
Run, program and fault: what a controller does when something goes wrong, and the safety functions that decide how much that costs.
