Understanding Delay Relay Functions
What is the difference between On Delay, Off Delay, Single Shot, Interval On and all other time delay functions?
Understanding the differences between all the functions available in time delay relays can sometimes be a daunting task. When designing circuits with time delay relays, you must ask questions such as what starts the time delay relay, whether timing starts from applying or releasing voltage, when the output relay is energized, etc.
Delay relays are just control relays with built-in delays. Their purpose is to control events based on time. The difference between relays and time delay relays is when the output contacts open and close: on control relays, it happens when voltage is applied and removed from the coil; on time delay relays, the contacts can be delayed for a certain amount of time before or after on or off.
Typically, time-delay relays are activated or triggered by one of two methods:
Application of input voltage
Turn the trigger signal on or off
These trigger signals can be one of two designs:
Control switches (dry contacts), i.e. limit switches, buttons, float switches, etc.
Voltage (commonly known as power trigger)
NOTE: Any time delay relay designed to use a dry contact to control the switch trigger actuation may be damaged if voltage is applied to the trigger switch terminals. Only products with a "power trigger" can use voltage as a trigger.
To aid understanding, some definitions are important:
Input Voltage Control voltage is applied to the input terminals. Depending on the function, the input voltage will start the device or make it ready to start when triggered.
Trigger Signal - On some timing functions, a trigger is used to start the device after an input voltage is applied. As mentioned above, this trigger can be a control switch (dry contact switch) or a power trigger (voltage).
Output (Load) - Each time delay relay has an output (mechanical relay or solid state) that will turn on and off to control the load. Note that the user must provide voltage to power the load switched by the output contact of the time delay relay.
Below are written and visual descriptions of how common timing functions work. The timing diagram shows the relationship between the input voltage, flip-flop (if present), and output. If you cannot find a product that matches your requirements or have any questions, Future Hi-Tech application engineers can provide technical information as well as product selection and application assistance. Email or call us for assistance.
Operation Delay After the input voltage is applied, the time delay (t) begins. At the end of the delay (t), the output is energized. The input voltage must be removed to reset the time delay relay and disconnect the output.
Interval After the input voltage is applied, the output is energized and the time delay (t) begins. At the end of the delay (t), the output is de-energized. The input voltage must be removed to reset the delay relay.
turn off delay
Power-off delay After the input voltage is applied, the delay relay is ready to be triggered. When the trigger is applied, the output is energized. After the trigger is removed, the time delay (t) begins. At the end of the delay (t), the output is de-energized. The application of any flip-flop during the delay resets the delay (t) and the output remains energized.
Momentary Interval After the input voltage is applied, the time-delay relay is ready to be triggered. After triggering, the output energizes and begins the delay (t). During the time delay (t), the trigger is ignored. At the end of the delay (t), the output is de-energized and the delay relay is ready to accept another trigger.
(Off first) After the input voltage is applied, the time delay (t) begins. At the end of delay (t), the output energizes and remains in this state for delay (t). At the end of the time delay (t), the output is powered down and the sequence repeats until the input voltage is removed.
(Turn on first) When the input voltage is applied, the output is energized and the time delay (t) begins. At the end of time delay (t), the output de-energizes and remains in this state for time delay (t). At the end of the time delay (t), the output powers up and the sequence repeats until the input voltage is removed.
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