Characteristics and working principle of digital time relay
Features of digital time relay
1. Air damped digital time relay is also called air bag type digital time relay. It delays according to the resistance caused by air compression. Its simple structure, cheap price and large delay range (0.4 ~ 180s) But the delay is low.
2. The electromagnetic digital time relay has a short delay time (0.3 ~ 1.6s), but its structure is relatively simple, and it is usually used in power-off delay occasions and DC circuits.
3. The principle of the electric digital time relay is similar to that of a clock. It uses the internal motor to drive the reduction gear to obtain a delay. This relay has high delay accuracy and a wide delay range (0.4 ~ 72h), but its structure is complicated and the price is very expensive.
4. Transistor-type digital time relay is also called electronic digital time relay. It uses delay circuit to delay time. This relay has high precision and small size.
How digital time relays work
Air-damped digital time relays are often used in AC circuits, which use the principle of air throttling through small holes to obtain time-delayed action. It consists of an electromagnetic system, a time delay mechanism and contacts.
Digital time relays can be divided into two types: on-delay and off-delay.
The air-damped digital time relay has a large time delay range (0.4 to 60s and 0.4 to 180s). It has a simple structure but low accuracy.
When the coil is energized (ac380v, ac220v or dc220v, dc24v, etc.), the armature and the pallet are attracted by the core and moved down momentarily to make the instantaneous action contact turn on or off. However, the piston rod and lever cannot fall with the armature at the same time, because the upper end of the piston rod is connected to the rubber film in the air chamber. When the piston rod starts to move downward under the action of the release spring, the rubber film is then concave downward, and the top The air in the air chamber becomes thinner and the piston rod is damped and slowly descends. After a certain period of time, the piston rod is lowered to a certain position, and the delayed contact action is pushed by the lever to open the break contact and close the close contact. The delay from the coil to the completion of the delay contact is the delay time of the relay. The length of the delay time can be changed by adjusting the size of the air hole of the air chamber with screws. After the attraction coil is de-energized, the relay is restored by the action of a recovery spring. The air is quickly exhausted through the air vents.