What would you use in a PLC-controlled system to learn the total accumulated time a motor has been running?

What would you use in a PLC-controlled system to learn the total accumulated time a motor has been running?

• A. Nonretentive timer
• B. Retentive timer
• C. Pulse counter
• D. Up-down counter

Answer: (B)

To learn the total accumulated running time of a motor, you need a timer that keeps its accumulated value across runs. A retentive timer does exactly that: it preserves the elapsed time in its accumulator even when the motor stops or power cycles, so the ET (elapsed time) value continues to grow with every on period. This lets you see the overall running time accumulated over multiple cycles, not just the current run. In contrast, a nonretentive timer resets its accumulated time when the input goes false or after a power event, so it only measures the current on‑time. Pulse counters and up-down counters track counts or position, not elapsed time, so they aren’t suitable for total running time.

To learn the total accumulated running time of a motor, you need a timer that keeps its accumulated value across runs. A retentive timer does exactly that: it preserves the elapsed time in its accumulator even when the motor stops or power cycles, so the ET (elapsed time) value continues to grow with every on period. This lets you see the overall running time accumulated over multiple cycles, not just the current run. In contrast, a nonretentive timer resets its accumulated time when the input goes false or after a power event, so it only measures the current on‑time. Pulse counters and up-down counters track counts or position, not elapsed time, so they aren’t suitable for total running time.