What does the PLC Counter Instruction do?

What does the PLC Counter Instruction do?

• A. It disables outputs
• B. It counts elapsed time
• C. It stores a preset
• D. It sets and resets the Done bit after it has been turned on and off a predetermined number of times

Answer: (D)

A PLC counter instruction counts discrete events, such as input transitions, rather than measuring time. It watches an input and increments its count each time the input changes (for example, a rising edge). The counter has a preset value that represents how many events to count. When the accumulated count reaches that preset, the Done bit is asserted, indicating the target number of events has occurred. If the counter is reset, counting starts again, so the Done bit can be set again after another cycle of on/off events. This behavior—tracking how many times a condition has happened and signaling completion with the Done bit after reaching the preset count—is why this option is correct.

A PLC counter instruction counts discrete events, such as input transitions, rather than measuring time. It watches an input and increments its count each time the input changes (for example, a rising edge). The counter has a preset value that represents how many events to count. When the accumulated count reaches that preset, the Done bit is asserted, indicating the target number of events has occurred. If the counter is reset, counting starts again, so the Done bit can be set again after another cycle of on/off events. This behavior—tracking how many times a condition has happened and signaling completion with the Done bit after reaching the preset count—is why this option is correct.