How an Off Delay Timer Works

off delay timer

How an Off Delay Timer Works

An off delay timer is used to control devices or systems. Unlike interval-on timers, which start timing when the input voltage is applied, off delay timers only begin after the voltage has been removed.

They have capacitors in their circuits which charge when the power is available to them. Once the power is withdrawn, the capacitors discharge and the timer contacts change over from NC to NO or vice versa.

Setting interface

An off delay timer is a type of time relay that can be used to control a wide range of devices and circuits. It has an on and off setting, and can be set by a button or knob. These types of timers are often used to control air-conditioning blower motors, coin-operated dryers in laundries, and gas valves. They can also be used for other applications, such as elevator door controls.

Off delay timers have a unique triggering mode. These timers have power applied all the time, but when they receive a signal, their contacts will transfer and the timer cycle will start. When the timing cycle ends, the contacts will return to their original state. Off delay timers can be triggered by a variety of events, but the most common is loss of power.

The OFF Delay Timer instruction is a ladder logic instruction that delays turning off an output by accumulating downward from a preset value toward 0 and then turning OFF the output. This is useful for a variety of industrial control applications and automation systems, such as a fan that must remain running for a few seconds after the compressor turns off. This is similar to the TON command, which is used to turn on a machine after another machine has turned off.

Coil energized

When an off delay timer is energized the coil starts counting the preset time. Once hot swap controller ic the accumulated time has reached the pre-set time the timer contacts change state from open to closed. The timer remains in this state until it loses power.

This type of timer is commonly used in star-delta starters and capacitive load starters. It is also a common component in industrial control systems. Unlike the other types of timing relays, these do not have instantaneous contacts that change state once the coil is energized. In order to initiate the timer, the input supply has to be applied continuously for a specified period of time.

The specifications of each off delay timer will tell you how long the coil can remain energized before the count stops and the contacts change over. These values will vary between manufacturers but it is recommended to keep the supply as close to the maximum value as possible.

Another specification to look out for is the minimum turn off voltage. This will tell you how low a voltage the coil can be before it must no longer remain energized. This is to ensure that the internal capacitors will charge correctly and that the timer performs as intended. The minimum turn off voltage is normally 1.2 VDC. Anything less and the relay will not be able to operate properly.

Contact changeover

When the off delay timer is energized, its contacts change state from open to closed. They remain in this state until the elapsed time set by the user is reached. These times can range from milliseconds to hours and days. In industrial control systems, they are commonly used to provide a delay before de-energizing an output signal or shutting down a process.

Unlike the older pneumatic off delay units, solid-state time delay relays do not require input voltage to be maintained while their contacts are changing state. This makes them more reliable and less expensive than pneumatic time delay units. They also have a number of additional functions not available on the pneumatic version.

On-delay timers are a common part of a star delta starter, where they are used to delay the switching of a delta contactor. In addition, they are used in air-conditioning systems to hold a blower motor for a specific period after the thermostat is activated. They can also be used to control electrical devices and motors for a specified time period, such as coin-operated dryers in laundries.

When the timer coil is energized, it starts counting down the preset delay time. This count is known as the accumulated time. When the accumulated time reaches the preset light driver time, the timer contacts change state; those that were open when the coil was not energized will go closed and those that were closed will switch to an open position. The timer will stay in this changed state until the coil is de-energized, which will cause its contacts to return to their initial positions.


An off delay timer works on the principle of capacitors. When it is powered on, the capacitors charge up to a certain level. On removing power, the timer continues to discharge its capacitors at a predetermined rate. This state is called the reset state. The timer will continue to operate until the time it is set for has elapsed.

Off delay timers are used in control applications where a specific action is to be initiated after a rung input goes false. This can help prevent overloading or damage to equipment, and it also reduces energy consumption. It can also prevent uncontrolled shutdown of equipment, reducing the risk of fires or explosions.

These timers can be programmed to a specified duration using adjustable settings. They are also available in a wide range of models and sizes. They can be triggered either with a switch or with an external pulse. They can be connected to any type of sensor and are suitable for a variety of applications.

The retentive timer has a MR pin, which is internally connected to VDD through a pull-up resistor (R MR). If the logic signal controlling MR is driven low, the RESET bit is asserted. Alternatively, the MR pin can be connected to GND to disable RESET. If RESET is asserted, the retentive timer’s accumulated value will be reset to zero.

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