A relay is an electrical control device used to convert a certain amount of electricity, such as voltage, current, or non-electricity, such as temperature, pressure, time, speed, etc., into a switch value to realize the automatic control function of the circuit.
It is an automatic switching element with isolation function, which is widely used in automatic control, mechatronics and power electronic equipment, and is one of the most important control elements.
The working principle of the relay and the contactor is the same. The difference is that the main contact of the contactor can pass a large current, while the contact of the relay can only pass a small current. Generally, the current is below 5A, so the relay can only be used for control circuits.
There are many types of relays
Relays are classified according to the input quantity and can be divided into voltage relays, current relays, time relays, speed relays, pressure relays, etc.;
According to the working principle, it can be divided into electromagnetic type, induction type, electric type, electronic type, etc.;
According to the purpose, it can be divided into control relays, protection relays, etc.
Generally speaking, our commonly used relays mainly include intermediate relays, voltage relays, current relays, time relays and thermal relays. Most of the relays used in our control circuits are electromagnetic relays, so electromagnetic relays are widely used with low voltage In the control system, let's introduce several commonly used relays respectively.
Intermediate relay
Intermediate relay is one of the most commonly used relays. Its structure is basically the same as that of contactors. Intermediate relays can replace small contactors when the load capacity is relatively small. It can also be used to expand the capacity and number of contacts, and is also used in control The intermediate signal is transmitted in the circuit, and the function of the intermediate relay is to control a large current with a small current, or to control a strong current with a weak current.
The intermediate relay is essentially a voltage relay, which operates according to the presence or absence of the input voltage. Generally, there are many pairs of contacts, and the rated current of the contact capacity is about 5A to 10A.
Intermediate relays are small in size and highly sensitive in action. Generally, they are not used to directly control the load of the circuit. However, when the load current of the circuit is below 5A-10A, it can also replace the contactor to control the load. The intermediate relay has many contacts, including 8-pin, 11-pin, and 14-pin relays. Different numbers of pins are actually divided into two open and two closed, three open and three closed, and four open and four closed types. You can see for details. Schematic diagram of the pins on the product.
Time Relay
The time relay is a very important component in the electrical control system. In many control systems, it is necessary to use the time relay to realize the delay control and play the role of delaying closing or opening in the circuit.
The time relay is an automatic control electric appliance that uses the principle of electromagnetic or mechanical action to delay the closing or breaking of the contact.
We can also say that a time relay is an electrical component used on a circuit with a lower voltage or a smaller current to turn on or off a circuit with a higher voltage and larger current.
The time relay is generally used to control the motor starting process with time as a function. There are many types of time relays, which can be divided into electromagnetic type, air damping type, electric type and electronic type according to their operating principles; according to the delay mode, they can be divided into power-on delay type and power-off delay type.
Let’s take a look at the power-on delay timer. There are coils, normally open and normally closed contacts in the pins of the relay. When it is switched on, proceed according to the instructions on the pins on the product. Give the relay working coil a control current. , The relay is closed, and the corresponding contact is turned on or off.
Current relay
The input of the current relay is current, which is a relay that acts according to the magnitude of the input current. The coil of the current relay is serially connected to the circuit to reflect the change of the circuit current. The coil has a small number of turns, a thick wire and a small impedance.
Current relays can be divided into undercurrent relays and overcurrent relays.
The undercurrent relay is used for undercurrent protection or control, the undercurrent protection in the electromagnetic chuck, the resistance switching control when the wound asynchronous motor starts, etc., the overcurrent relay is used for overcurrent protection or control, such as the overcurrent in the crane circuit protect.
Voltage relay
The input of the voltage relay is the voltage of the circuit, which acts according to the input voltage. Similar to current relays, voltage relays are also divided into undervoltage relays and overvoltage relays.
The voltage relay is connected in parallel in the circuit when it is working, so the coil has many turns, the wire is thin, and the impedance is large. It reflects the voltage change in the circuit and is used for the voltage protection of the circuit. Voltage relays are commonly used in power system relay protection, but are rarely used in low-voltage control circuits.
The above is the introduction of our commonly used relays. Have you mastered it?
