What is a Timer Relay? Working Principle and Selection

Most of those dealing with electrical work know what a time relay is. It is a very popular and well-known device in the energy market. Timer relay has been known since 1929 for its reliable designs that provide long service lives with low maintenance costs. With the effective operating principle, the timer relay gives you the option of choosing among functions and time delay ranges to ensure that you receive the perfect timer to fit your needs.

Keep reading to understand the main types, applications and selection parameters of timer relays.

What is a Timer Relay?

A timer relay is an electrical component that controls the on and off cycles of a device by using a timed switch. It is often used to automate processes and control power to devices in various applications. Timer relays can be set to activate and deactivate at specific times or intervals and can be controlled by manual inputs or triggered by external events.

Timer relays typically allow the user to set the time delay which can range from a few milliseconds to several hours or even days depending on the application requirements. They can also be programmed to repeat the timing cycle automatically or triggered by an external signal.

Timer relays can be pneumatic, solid-state, or motor-driven mechanisms. Solid-state timers are normally incorporated within so-called programmable controllers (PCs) which can be programmed to give the desired cycling period to any number of contacts.

How Does a Timer Relay Work?

The operation principle of a timer relay is as follows:

First, the supply voltage is applied to the timer relay.
Second, the microprocessor starts booting.
In the next step, the microprocessor reads the information from the interface. The interface consists of different adjustment possibilities on the front face of the timer. There the time function, time range and the fine adjustment of the desired delay time have to be set through rotary switches and potentiometers.
In the fourth step, the microprocessor reads the information of the control inputs such as the control input for starting the delay. This information for the timer is to start the operation and it is called the ‘start impulse’ or the ‘trigger’.
Now the timer operates.
When the selected time delay is complete, the output relay energizes/de-energizes.
After the energization of the output relay, the load current powers the connected device like a contactor.

Time relays — *Rail-mounted timer relays*

Timer Relay Functions

Timer relays provide a wide range of selectable functions so that users can customize their specific machine operations. There are several timing functions for timer relays. Some of them are:

1. On delay

When the supply voltage is applied and the delay time is over, the output contact changes the position. (For example, a fan starts working) And when the supply voltage breaks down, output contact returns to the first position. (And the fan stops)

2. Off-delay

Output contact changes the position when the supply voltage is applied. (For example, The fan starts working immediately) But when the supply voltage breaks down, output contact returns to the first position for the defined time. (The fan keeps working for the defined time)

3. Multifunction

A multifunctional time relay is a type of timer with various types of timing functions. Different controlling functions can be selected and applied by using a multifunctional timer. It is perfect for many applications from basic to industrial controls.

Below you can see all the timing functions of timer relays. These functions should be checked from the catalogs of the manufacturers.

Time relay types and functions — *List of timer relay functions*

Timer Relay Selection Parameters

When selecting a timer relay, these parameters should be considered:

Supply voltage.
Timing functions. (such as off delay, on delay, multifunction, etc..)
The number of output contacts.
Timing ranges. (For example 0.05 s – 100 h, 05 s – 10 min)
Indication of operational states. (LED indication)
Special features like voltage-related triggering, volt-free triggering and remote potentiometer connection.
Contact rating
Mounting style

These features we have listed are general. Features may vary from brand to brand. The manufacturer catalogs and user manuals should be checked before making a selection.

Technical Definitions

Input voltage: The input voltage of a timer relay is the control voltage applied to the A1-A2 terminals. The input voltage will either initiate the relay or make it ready to start as soon as a trigger signal is applied.

Trigger signal: A trigger signal is used to initiate the relay after the input voltage has been applied.

Output: Every time delay relay has an internal relay (usually mechanical) with contacts that open & close to control the load.

There are three types of output contact

CO: When the coil is de-energized, it closes the circuit between the common point C and NC contact. When the coil is energized, it closes the circuit between the common point C and the NO contact.

NC: A contact that is closed without being actuated is called a normally closed contact.

NO: A contact that closes when actuated is called a normally open contact.

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