Which instruction increases the accumulated value by the amount of time it is de-energized?

The correct response to this question is that the instruction which increases the accumulated value by the amount of time it is de-energized is the timer-off instruction, commonly referred to as TOF (Timer Off).

This instruction is utilized in programmable logic controllers (PLCs) to monitor how long a certain device or condition remains in an off state. When a TOF instruction is implemented, it begins counting the time once the control input is de-energized, allowing the system to track the duration the input stays off. The accumulated value it produces indicates the total time that the condition has been inactive or de-energized.

In practical applications, the TOF function is particularly valuable for scenarios where knowing the duration of inactivity is critical for control processes or for initiating subsequent actions after a specific period of de-energization has elapsed. This differentiates from other instructions that either count when energized or perform different counting operations related to counting up or down states.