Timer Relay: Working Principle, Applications, Basics

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. Time relay has been known since 1968 for its reliable designs that provide long service lives with low maintenance costs. With the effective operating principle, timer relays give you the option of choosing among functions and time delay ranges to ensure that you receive the perfect timer to fit your needs.

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

What is a timer relay?

A timer relay, following the energization of its coil, changes the status of its contacts cyclically. Usually, the time period during which the contacts could remain closed or open is externally adjustable, and the cycling period can vary from some milliseconds to several hundred hours. The number of controlled contacts and the cycling period depends on the design of the timer.

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 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 is powering the connected device like a contactor.

Timer relay types

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

On delay timer relay

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

Off delay timer relay

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 turns back to the first position for the defined time. (The fan keeps working for the defined time)

Multifunction timer relay

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.

Timer relay applications

Timer relays are suitable for a wide range of applications, including:

• Machines: single machine, star-delta motor starting, industrial automation and processes
• Buildings: lighting control, automatic doors, car park barriers, roller shutters
• Water segment: pump controls and irrigation systems
• HVAC: fans and centralized water systems

Other application examples:

Cyclic switching of machinery, for example, the weekly startup of a fan to prevent them from sticking or the flushing of pipes to keep them clear.

Lighting control, for example, the delayed switching of multiple rows of lamps in production facilities or green-houses.

Time-controlled start-up or shut down of machinery equipment, for example, the delayed switch-off of conveyor belts or the successive shut down of a plant.

Alarm triggering in case of fault detection, for example, to allow the flashing of a lamp in industrial applications or rolling stock.

Star-delta motor starting, For example, to reduce starting current with changeover delay to prevent interphase short-circuits.

Pushbutton for crosswalks, for example, when you push the button for a walk signal, the signal light changes from don’t walk to walk after a delay.

Car wash, For example, the car wash operates for five minutes when money is inserted.

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.

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.