Digital timers keep track of timing; to trigger an action, to start timing once triggered by an action, or both. Some products are programmable while others may be fixed at a set internal time and function. In addition to the number and type of functions, these devices differ in terms of time range settings.
Suppliers of digital timers offer meter, delay-on, delay-off, one-shot, recycle, and interval delay timers.
- Timer meters, indicators, or totalizers are used in applications for display of elapsed process time or tracking running time of factory machinery.
- Delay-on timers require a predetermined period of time to pass between when the timer receives its input signal and when the output is energized. At the end of the time delay, the contacts open or close. If the contact is normally open (NO), then the load energizes at the end of the time delay. If the contact is normally closed (NC), then the load de-energizes after the time delay. Removing power resets the time delay and output. This capability is also called on-delay, delay on make, delay-on operate, operate delay, pre-purge delay, and delay-on energization.
- Delay-off timers start their timing functions when the power supply is interrupted. When the power is initially supplied, the output relay contacts react immediately. When the power supply is removed, the output relay contacts remain in the activated position and the time period starts. When the time has elapsed, the output relay contacts release. This capability is also called delay on release, delay on break, release delay, post-purge delay, and delay on de-energization.
- One shot timers are designed so that when power is applied to the timer, the contacts change position immediately and remain changed for the set period of time after the timer has received power. After the set period of time has passed, the contacts return to their normal position. These devices are also called pulse formers.
- Interval delay timers are the opposite of delay-on devices in that the relay is energized immediately upon application of the supply or closure of the switch input, and goes off at the end of the period. Interval delay is sometimes called delay pulse.
- Recycle timers act so that the closing of the control switch starts the cycling function. The load continues to turn ON and OFF at regular time intervals as long as the control switch is closed. The cycling function stops when the control switch is open. This function is sometimes called a flasher, or pulse generator.
Other important functions of digital timers include delay cycles, position indicators, preset counters, arithmetic functions, controllers, and counter and timer combinations.
Digital timers have both common consumer uses and large industrial uses. Timers are used in process control equipment to assist in process regulation, they are installed in industrial equipment to record its use and age, and they are used as consumer electronics for household use and recreational use.