Instrumentation (INS) Practice Test

OSR is a one-shot rising pulse in PLC programming. It watches the input and, when it detects a transition from off to on, it outputs true for exactly one PLC scan. Even if the input stays high after that, the OSR output resets to false on the next scan, producing a single, punctual signal for each rising edge. This edge-triggered behavior lets you trigger actions only once per activation—perfect for starting a timer, incrementing a counter once per press, or feeding another element with a single pulse. It’s different from a normal contact, which remains true as long as the input is on, and it isn’t describing a timer function or a sensor or status report.