Fundamentally, both timers are similar in that they provide a delay period that the relay remains energised for from an initial trigger. However, the trigger method for both is different.
True Delay Off – This timer utilises storage capacitors internally which retain their charge when the power is removed to the timer. This is sufficient to allow timing periods of up to 10 minutes to be achieved. Operation is straight forward in that power is applied to the timer and the internal relay energises. As soon as power is removed, timing starts but the relay remains energised. When the timing period has elapsed, the relay will de-energise.