What does the Count Up (CTU) instruction do in a PLC counter?

What does the Count Up (CTU) instruction do in a PLC counter?

• A. Increases the instruction tag's Accumulated value by one each time the rung containing the instruction goes from false to true.
• B. Decreases the instruction tag's Accumulated value by one each time the rung containing the instruction goes from false to true.
• C. Resets the Accumulated value to zero when the rung becomes true.
• D. Sets the Done bit immediately when scanned.

Answer: (A)

Count Up increments the accumulated value by 1 on every rising edge of the rung's truth. In other words, when the rung goes from off to on during a scan, the accumulator increases by one. If the rung stays true across scans, it does not keep counting each time; it only counts when the input transitions from false to true. The counter also uses a preset to determine when the Done bit is set, signaling the count has reached the target. This edge-triggered, single-increment-on-rise behavior is exactly what defines a Count Up counter.

Count Up increments the accumulated value by 1 on every rising edge of the rung's truth. In other words, when the rung goes from off to on during a scan, the accumulator increases by one. If the rung stays true across scans, it does not keep counting each time; it only counts when the input transitions from false to true. The counter also uses a preset to determine when the Done bit is set, signaling the count has reached the target. This edge-triggered, single-increment-on-rise behavior is exactly what defines a Count Up counter.