What is a timer? Structure, operating principle and classification of timer

What is a timer?

A timer (time relay) is a device whose contacts (closed or opened) are slower than the time when a control signal is received. This device can adjust the RTG time delay. The timer is used in protection and automation schemes, in systems that control technological processes. The timer also has the function of creating the required maintenance time when transmitting signals from one device to another.

What is the composition of the timer?


Including voltage coil 12, the circuit from static 11, steel core 10 and springs 9. It receives voltage from the operating power source. That means the power supply is controlled.

Time mechanism

Includes drive gears (23) rigidly connected to the brake unit (4). This gear is driven by springs (18) and transmits the motion to the gears (22) to rotate the contact point (21). The main part of the time mechanism is a system of gears (16), (15), (13) connected to the rotating contact shaft by friction wheels (17). It rotates gear 3 to transfer motion to the pendulum mechanism consisting of ratchets (14), hook (1) and vibrator (2). The pendulum mechanism to keep the rotation speed of dynamic contact is uniform, similar to that of a clock mechanism.

Main contact

Includes static contact head (22) and dynamic contact head (21). In addition, it has two auxiliary contacts closed, cutting spacetime: positive contacts (5-8) and negative contacts (5-7).

Cấu tạo của timer

Structure of a timer

What is the working principle of the timer?


When powering the ON DELAY timer coil, the impact contacts do not take into account instantaneous state transitions. (The contacts are often opened, often closed.) Impact contacts have a constant time. After a predetermined period of time, time-sensitive contacts will transition. That state will remain in this state.

When stopping supplying power to the coil, all contacts immediately return to their original state.

Time-sensitive contact symbols:

  • Contact normally open, close slowly, open quickly.
  • Contact normally closed, opened slowly, closed quickly.


When powering the OFF DELAY timer coil, the contacts act immediately and maintain this state.

When the coil is stopped, all contactors do not take the time to return to their initial state. After a predetermined period of time, timed impact contacts will return to their original state.

The Contacts are normally open, close fast, open slowly.
The contacts are normally closed, opened quickly, closed slowly.

Distinguish the type of timer?

Currently, in the market you can easily find the following types of time relays:

  • Electronic timer

Timer điện tử

Electronic timer

  • Mechanical timer

Timer cơ autonics

Autonics mechanical timer

24h timer: the 24-hour circulating timer series has a simple feature. Therefore, this device is used a lot in lighting systems and many other applications.

Timer 24h

24h timer

-> Buy Genuine Idec Timer: HERE

Applying off delay to control lighting public areas for high-rise buildings

Public areas such as apartment corridors, stairs are places that everyone has the right to share. So the lighting system must operate 24/24. So the problem here is how to control the lights in this area. From there, it can be both economical and convenient.

Currently, most of the constructions in Vietnam have no reasonable solution for these public areas. Some ways the lights work are:

  • These area lights are now turned on 24/24.
  • There are switches at the position of corridors, stairs for people to control themselves.
  • Building management will turn on and off these lights at certain times.
  • Use a motion sensor to turn on / off the light….

All these measures have shortcomings. For example, waste of electricity, time and effort … So the best solution to solve all these problems is to use Delay-off in combination with motion sensors in several locations. This is both convenient and energy-saving, but the installation cost is not high.

> Learn more: What is HMI?

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