In PLC terminology, an OSR (one-shot rising) is true for how long?

• A. It resets the PLC when triggered.
• B. It is functionally equivalent to a latch.
• C. It stays true for only one PLC scan.
• D. It activates on every scan.

Answer: (C)

One-shot rising generates a brief pulse on a rising edge. When the input switches from off to on, the OSR output goes true for exactly one PLC scan and then returns to false, even if the input remains high. This makes it ideal for triggering something once per transition rather than for the duration the input is high. Since it pulses only on the rising edge, it won’t be active on every scan, and it isn’t a reset or a latch that holds state. If the input goes low and then high again, a new pulse occurs.