Using Time Delay Relays to Cycle a Traffic Signal

Wednesday: December 19, 2018 : Time Delay Relays


Issue:

I have an old traffic signal that I would like to cycle through the Green-Yellow-Red lights. Can this be done with time delay relays?

Solution/Resolution:

This simple solution can be done with one Interval ON (TD1) & two Single Shot (TD2 & TD3) time delay relays. Wire the three time delay relays & traffic signal per the following diagram and the system will operate as described below. Set the time delay period t1 on each timer to the same value. NOTE: With this circuit, the traffic signal lights & time delay relays must use the same voltage:

How It Works

  • Upon application of the input voltage, TD1 (Interval ON) will energize and turn on the GREEN light. This light will remain ON for the t1 period of TD1.
  • When TD1 times out & de-energizes, the GREEN light is turned OFF. This also re-closes the relay contact between Pins 5 & 8 from TD1, which acts as the trigger switch to TD2 (Single Shot), energizing TD2 & turning on the YELLOW light. This light will remain ON for the t1 period of TD2.
  • When TD2 times out & de-energizes, the YELLOW light is turned OFF. This also re-closes the relay contact between Pins 8 & 11 from TD2, which acts as the trigger switch to TD3 (Single Shot), energizing TD3 & turning on the RED light. This light will remain ON for the t1 period of TD3.
  • When TD3 times out & de-energizes, the RED light is turned OFF and Input Voltage will be re-applied to TD1, starting the cycle all over again.

NOTE: This circuit will only work when using Single Shot time delay relays where applying Input Voltage after the Trigger Switch has been closed will NOT energize the relay. Therefore, the following Macromatic Single Shot time delay relays can be used in this application: TR-515 (with Date Codes 1138 or later), TR-615 (with date Codes 1707 or later), TR-681 (multi-function set up as a Single Shot), TD-781 (multi-function set-up as a Single Shot) and TD-881 (multi-function set-up as a Single Shot). A TR-515 or a TR-615 product with Date Codes earlier than just listed WILL NOT WORK.

Using Time Delay Relays to Cycle a Traffic Signal

For additional information, please contact Macromatic Technical Support at 800-238-7474.

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