Which type of timer accumulates total time and retains this value even during de-energization?

A retentive timer is designed specifically to accumulate total time and retain that value even when the system is de-energized. This feature makes retentive timers particularly useful in applications where it is important to keep track of elapsed time across power cycles. When the power is restored, the timer continues counting from where it left off, rather than resetting to zero, which allows for accurate monitoring of time-dependent processes.

In contrast, non-retentive timers reset their accumulated time to zero when de-energized. This means that any time counted before the de-energization is lost, which limits their application in scenarios where continuous time tracking is necessary.

On-delay timers and off-delay timers are specific types of timers that control the activation and deactivation of outputs based on preset time intervals but do not inherently retain their count when power is lost. Their primary function is related to the timing of events when the condition changes, rather than the accumulation and retention of total time.

Thus, for scenarios requiring the retention of accumulated time despite interruptions, a retentive timer is the appropriate choice, underscoring its value in programming contexts where historical timing data is critical.