(1). First understand the necessary conditions

① The power supply voltage of the control circuit, the maximum current that can be provided;

②The voltage and current in the controlled circuit;

③ How many groups and what form of contacts are required for the controlled circuit. When choosing a relay, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should provide enough working currently to the relay, otherwise, the relay pull-in is unstable.

(2). After checking the relevant information to determine the conditions of use, you can search for the relevant information to find out the model and specification number of the relay you need. If you already have a relay on hand, you can check whether it can be used according to the data. Finally, consider whether the size is appropriate.

(3). Pay attention to the volume of the appliance. If it is used for general electrical appliances, in addition to considering the chassis volume, the small relay mainly considers the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used.

Relay is an automatic switching element with an isolation function. It is widely used in remote control, telemetry, communication, automatic control, mechatronics, and power electronic equipment. It is one of the most important control elements. The relay generally has an induction mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); Between the input part and the output part of the relay, there is an intermediate mechanism (drive part) that couples and isolates the input quantity, processes the function and drives the output part.

(1) Expand the scope of control. For example, when the control signal of the multi-contact relay reaches a certain value, the multiple circuits can be switched, broken, and connected at the same time according to the different forms of the contact group.

(2) Zoom in. For example, sensitive relays, intermediate relays, etc., can control high-power circuits with a very small amount of control.

(3) Integrated signal. For example, when multiple control signals are input to the multi-winding relay in a prescribed form, a predetermined control effect is achieved through comparison and synthesis.

(4) Automatic, remote control, and monitoring. For example, the relay on the automatic device, together with other electrical appliances, can form a program control circuit to realize automatic operation.