Important questions to ask.
Understanding the differences between all the functions available in time delay relays can sometimes be a daunting task. When designing circuits using time delay relays, several questions must be asked.
- What initiates a time delay relay?
- Does the timing start with the application or release of voltage?
- When is the output relay energized?
WHAT IS THE DIFFERENCE BETWEEN A CONTROL RELAY & A TIME DELAY RELAY?
Time delay relays are simply control relays with a time delay built in. Their purpose is to control an event, based on time. The difference between relays and time delay relays is when the output contacts open and close:
- With a control relay, the output contacts open and close when voltage is applied and removed from the coil
- With a time delay relay, the contacts can open or close before or after some time delay
A time delay relay needs a trigger.
Typically, time delay relays are initiated or triggered by one of two methods:
- Application of input voltage
- Opening or closing of a trigger signal
These trigger signals can be one of two designs:
- A control switch (dry contact), i.e., limit switch, push button, float switch, etc.
- Voltage (commonly known as a power trigger)
CAUTION:
Any time delay relay that is designed to be initiated with a dry contact control switch trigger could be damaged if voltage is applied to the trigger switch terminals. Only products that have a “power trigger” should be used with voltage as the trigger.
Useful definitions
Input Voltage – control voltage applied to the input terminals. Depending on the function, input voltage will either initiate the unit or make it ready to initiate when a trigger is applied.
Trigger Signal – on certain timing functions, a trigger is used to initiate the unit after input voltage has been applied. As noted above, this trigger can either be a control switch (dry contact switch) or a power trigger (voltage).
Output (Load) – every time delay relay has an output (either mechanical relay or solid state) that will open and close to control the load.
Note: The user must provide the voltage to power the load being switched by the output contacts of the time delay relay.
Learn more about Macromatic’s Time Delay Relays functions.