Time relays setting explained

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Time relays are used in control switching operations involving time delay. Most of these time relays have multiple time setting ranges and most of them are explained below.


Time Delay Definition

Time relays perform either on-delay or off-delay timing. An arrow is used to denote the function of the timer. An arrow pointing up indicates an on-delay timing action, while an arrow pointing down indicates an off-delay timing action.

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On-delay and off-delay timers can turn their connected loads on or off, depending on how the timer’s output is wired into the circuit. The term “on delay” indicates that a preset time must pass after the timer receives a signal to turn on before the timer’s contacts change state.

The term “off delay” indicates that a preset time must pass after the timer receives a signal to turn off before the timer’s contacts change state.

 

On-Delay, Timed Closed Timer

The following illustration shows an example of an on-delay, timed closed timer, also called a normally open, timed closed (NOTC) timer. In this example, The timing relay (TR1) has been set for an on delay of 5 seconds.

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When S1 is closes, timer TR1 begins timing. After 5 seconds, TR1 contacts close, and pilot light PL1 turns on. When S1 opens, timer TR1 de-energizes, and TR1 contacts open immediately, turning off pilot light PL1.

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On-Delay, Timed Open Timer

The following illustration shows an example of an on-delay, timed open timer, also called a normally closed, timed open (NCTO) timer. The timing relay (TR1) has been set for an on delay of 5 seconds.

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When S1 closes, timer TR1 energizes. After 5 seconds, TR1 contacts open, and pilot light PL1 turns off. When S1 opens, timer TR1 de-energizes, and TR1, contacts close immediately, turning on pilot light PL1.

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Off-Delay, Timed Open

The following illustrations shows an example of an off-delay, timed open timer, also called a normally open, timed open (NOTO) timer. The timing relay (TR1) has been set for an off delay of 5 seconds.

When S1 closes, open TR1 contacts open immediately, and pilot light PL1 turns on.

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When S1 opens, timer TR1 begins timing. After 5 seconds, TR1 TR1 contacts open, and pilot light PL1 turns off.

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Off-Delay, Timed Closed

The following illustraton shows an example of an off-delay, timed closed timer, also called a normally closed, timed closed (NCTC) timer. The timing relay (TR1) has been set for 5 seconds.

When S1 closes, TR1 contacts open immediately, and pilot light PL1 turns off.

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When S1 opens, timer TR1 begins timing. After 5 seconds, timer TR1 contacts close, and pilot light PL1 turns on.

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Instantaneous Contacts

Timing relays can also have normally open or normally closed instantaneous contacts. In the following example, when switch S1 closes, TR1 instantaneous contacts close immediately, and pilot light PL1 turns on.

After a preset time delay, TR1 timing contacts close, and pilot light PL2 turns on.

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