10 Basic Timer Control: On-delay and off-delay

Types of Time-delay timer relays

- On-delay - Off-delay

Common timing mechanisms

- Pneumatic timers - Solid-state timers - Motor driven Timers

Time-Delay Relay components

- coil - Contacts - Timing mechanism

Application of an On-Delay Timer Relay

A centrifugal air compressor, which needs the compressor motor to start without a load. Contacts remain in their normal states until the timer has finished it's time delay. when the preset time has been reached, the contacts are moved to their energized state, causing the motor to be engaged to it's load.

Time-delay Function

A type of control relay that changes the state of it's contacts after a predetermined time has elapsed.

One common method of unloading the compressor motor during start up is to use a _________________ with a timer relay.

Control Circuit

Application of Time-Delay Relay

Electric washers and dryers

On-Delay Timer Relay Reset

If the push-button is released before the timer times out, the coil will de-energize and the timer of the relay will reset to zero.

N.C.T.O.

Normally closed time open

N.O.T.C.

Normally open time closed

Application of an Off-Delay timer delay

The cooling fan on an overhead projector. When the projector lamp is turned on, the timer coil is energized causing the times contacts to move to their energized positions and turn the fan on. The timed contacts remain in their energized state while the timer is running. the fan remains on, cooling the hot projector bulb. When the preset time is reached, the contacts are allowed to return to their normal states, turning the cooling fan off.

Function of an On-Delay Timer Relay

When it's coil is energized, the relay's timing mechanism begins to run but it's contacts remain in their normal state. once a preset time delay is reached, the contacts move to their energized states. The contacts remain in there energized states until the coil is de-energized.

Function of an Off-Delay Timer Relay

When it's coil is energized, the timer's contacts immediately move to their energized states. However, the timing mechanism does not operate until the coil is de-energized. Once the timer is de-energized, the timer starts running, during which time contacts remain held in their energized state.

Operation of On-Delay Timer Relay

When the coil 1 TR is de-energized the timer relay contacts are in their normal states and the internal clock is reset to zero. Next, the coil 1TR is energized this causes the timers internal clock to run but the contacts remain in their normal states.

May On-Delay and Off-Delay timers contacts have N.O. and N.C.?

Yes