2 working principle and characteristics
When the input quantity (such as voltage, current, temperature, etc. ) reaches the specified value, the relay opens or closes the controlled output circuit. Input can be divided into two categories: electrical quantities (such as current, voltage, frequency, power, etc. ) and non-electric quantities (such as temperature, pressure, speed, etc. ). The relay has the advantages of fast action, stable operation, long life and small size. Widely used in power protection, automation, sports, remote control, measurement and communication equipment.
3 working principle and characteristics of electromagnetic relay
Electromagnetic relay generally consists of iron core, coil, armature and contact reed. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, thus generating an electromagnetic effect. Under the attraction of electromagnetic force, the armature overcomes the pulling force of the return spring and attracts the iron core, thus driving the moving contact of the armature to attract the stationary contact (normally open contact). When the coil is powered off, the electromagnetic attraction disappears, and the armature will return to its original position under the reaction of the spring, so that the moving contact and the original static contact (normally closed contact) are disengaged. In this way, it is attracted and released, so as to achieve the purpose of making and breaking the circuit. For the normally open contacts and normally closed contacts of relays, we can distinguish them as follows: the static contacts that are disconnected when the relay coil is not energized are called "normally open contacts"; Static contacts in the on state are called "normally closed contacts". Relays generally have two circuits, namely, a low-voltage control circuit and a high-voltage working circuit.
4.■ Relay classification ■
There are many classification methods of relays, which can be classified according to the operating principle, overall size, protection characteristics, contact load, product use and so on.
First of all, according to the principle of action
1. electromagnetic relay
A relay that generates a predetermined response through the relative movement of mechanical parts under the action of current in the input circuit.
It includes DC electromagnetic relay, AC electromagnetic relay, magnetic latching relay, polarization relay, reed relay and energy-saving power relay.
(1) DC electromagnetic relay: an electromagnetic relay whose control current is DC in the input circuit.
(2) AC electromagnetic relay: an electromagnetic relay whose control current is AC in the input circuit.
(3) Magnetic latching relay: Magnetic steel is introduced into the magnetic circuit. After the relay coil is powered off, the armature of the relay can still maintain the state when the coil is powered on, and there are two stable States.
(4) Polarized relay: A DC relay whose state changes according to the polarity of input excitation.
(5) Reed relay: A relay that opens, closes or switches lines through the action of the reed sealed in the tube, which has the dual functions of contact reed and armature magnetic circuit.
(6) Energy-saving power relay: The control current in the input circuit is AC electromagnetic relay, but its current is large (generally 30- 100A), and its volume is small, which has the function of saving electricity.
2. Solid state relay
A relay, whose input and output functions are completed by electronic components, without mechanical moving parts.
3. Time relay
When the input signal is added or deleted, the output part needs to be delayed or limited to a specified time before the relay of the controlled line can be turned off or disconnected.
4. Temperature relay
A relay that starts to work when the outside temperature reaches a specified value.
5. Wind speed relay
When the wind speed reaches a certain value, the controlled circuit will be turned on or off.
6. Acceleration relay
When the acceleration of the moving object reaches the specified value, the controlled circuit will be turned on or off.
7. Other types of relays
Such as optical relay, acoustic relay, thermal relay, etc.
Second, according to the overall size.
See table 1.
Table 1 Classification of overall dimensions of relays
Name definition meaning
Relay with the longest side dimension of miniature relay not greater than10 mm.
Relay with the longest side dimension greater than10mm but not greater than 25mm.
A relay whose longest side dimension is greater than 25mm but not greater than 50mm.
Three, according to the contact load points
See Table 2.
Table 2 Classification of relay contact load
Name definition meaning
Micro-power relay is less than 0.2A relay.
Weak current relay 0.2 ~ 2A relay.
Medium power relay 2 ~ 10a relay.
High Power Relay 10A Relay.
Energy-saving power relay 20A- 100A relay
Fourth, according to the characteristics of protection
See table 3.
Table 3 Classification of relay protection characteristics
Name definition meaning
Sealed relay seals the contact and coil in a metal cover by welding or other methods, with low leakage rate.
Plastic-sealed relay uses sealant to seal the contact and coil in a plastic cover, which has high leakage rate.
Dust-proof relay A relay that covers contacts and coils for protection.
A relay that protects contacts, coils, etc. No protective cover
Five, according to the use of points
See Table 4.
Table 4 Classification of relay uses
Name definition meaning
Communication relays (including high-frequency relays) have a contact load range from low level to medium current, which does not require high environmental conditions.
Machine tool relay contacts used in machine tools have high load power and long service life.
Relays for household appliances require good safety performance.
Automobile relay The relay switch used in automobile has high load power and strong shock and vibration resistance.