Time relay is a kind of voltage relay with delay contact, which has two kinds of delay characteristics: power on delay and power off delay; The contact also has two kinds of instantaneous action and time delay action. The time relay is generally used as an auxiliary element in various protection and automatic devices, so that the action of the controlled element can get the required time delay.
According to the delay mode, it can be divided into the following two categories:
1. Power off delay type. This relay is opposite to the former. When the input signal (power on) is obtained, the executive part outputs the signal immediately. When the input signal disappears, the relay can recover to the state before action after a certain delay. The time from the coil power off to the contact reset is the power off delay time.
2. Power on delay type. When the relay coil obtains the input signal (or is powered on), it immediately starts to delay. After the delay, its executive part (i.e. contact) outputs the signal (i.e. action). When the input signal disappears, the relay will return to its original state. The action condition, that is, the time (T) from the coil power on to the contact action, is called the power on delay time.
The time relay can be divided into the following two types according to the operation principle:
1. Electrical time relay. It can be divided into electric type, counter type, thermistor type and resistance capacitance type (including electromagnetic type and electronic type).
2. Mechanical time relay. It can also be divided into four types: damping type (including oil damping type, air damping type or air bag type, electromagnetic damping type), mercury type, clock type and bimetallic plate type.
At present, electromagnetic damping type, air damping type, motor type and electronic time relay are widely used.