Time relay, which is very common as an actuator in electrical equipment control systems, starts to record the time according to the set time after the coil is connected, and the normally open contact is closed at the end of the time, and the normally closed contact is disconnected to perform the next step.
In the circuit, it mainly has the functions of delay closing, delay disconnection, and cyclic action.
In the mine flameproof feeder switch electronic control system, the role of the time relay is to delay the closure, that is, after the feeder switch from closing to opening, the next closing cannot be carried out immediately, and it must go through a certain time delay buffer to prevent continuous impact on the closing coil, resulting in burnout of the closing circuit.
In the star-delta step-down starting circuit of the motor, the time relay plays the role of delayed disconnection, that is, pressing the closing button, starting the return route to let the motor star solution run, the delay ends, the contact is disconnected, and the switch becomes the triangle solution, and the power runs for a long time.
Air conditioning systems, water supply and drainage systems, lighting systems, and reciprocating systems for machine tools all use the cyclic action of time relays.
The working principle of the time relay is divided into air damping type, electronic type and electric type according to the accuracy of use.
There are many electricians who can't tell whether the time relay is delayed closed or delayed when looking at the electrical schematic, in fact, there is a trick to identify: whether the semicircle is in front or behind, the direction of the semicircle mouth is the direction of the delay contact action.
The working principle of the time relay is divided into air damping type, electric type and electronic type according to the accuracy of use.
Air damped.
It is mostly used in machine tool control, and the structure is mainly composed of electromagnetic coils, iron cores, springs, and rubber films.
The operating principle of the delayed disconnect air damping time relay is that when the coil of the relay is energized, the iron core drives the spring to act, quickly compresses the rubber film air chamber, and closes the contact instantaneously through the lever.
When the coil loses power, the core moves under the action of the spring, and the rubber film in the air chamber is slowly deflated to reach the lever balance point, so that the contact is disconnected, and the control point is disconnected.
The action principle of the delayed closing type air damping time relay is the opposite of that of the delayed disconnect type, after the coil is energized, the spring action compresses the rubber film of the compressed air chamber and slowly inflates it to reach the lever balance point and the contact is closed.
When the coil loses power, the core acts, and the rubber film in the air chamber is also quickly filled with gas, so that the lever is instantly unbalanced and the contact is disconnected.
According to the above introduction, it can be seen that the delay effect of the air damping time relay is mainly determined by the degree of inflation and deflation of the rubber film, of course, the adjustment of the delay time is controlled by adjusting the throttling degree of intake and exhaust.
This kind of time relay has a simple structure, low cost, and a relatively large delay range, which is suitable for equipment with low control accuracy requirements.
Electric. The electric time relay has a complex structure, mainly relying on the motor to drive the gear to rotate, just like the washing machine timer, to reach the node of the gear rotation, and the cam pushes the trip mechanism to achieve the corresponding delay closure or delay disconnection.
This kind of time relay has high delay accuracy and a wide range of time adjustment.
Electronic. Electronic time relay, small size, long life, no mechanical structure, wide adjustment range and high precision, is widely used in pumps, boilers, etc.
The time relay is drawn differently in the circuit schematic due to the different direction of the delay action, but the symbols are all unified as KT.
With the development of industrial technology, time relays are gradually replaced by industrial control PLC software-level time relays.
As the saying goes: when the times abandon you, they will not say goodbye to you.
The industrial technology of relay control is gradually being eliminated, and we, as coal mine electricians, should follow the trend of the times and strive to learn new knowledge and new skills. to cope with the unknown future, are you right!