Relay, also known as electric stage, is an electronic control device, which has a control system (also known as input circuit) and the control system (also known as output circuit), usually used in automatic control circuit, it is actually a smaller current to control a larger current "automatic switch". Therefore, it plays the role of automatic regulation, safety protection, and conversion circuit in the circuit. The relay coil is represented in the circuit by a long box symbol, if the relay has two coils, draw two long boxes side by side. At the same time in the long box or next to the long box marked with the relay text symbol "J". Relay contacts have two methods of representation: one is to draw them directly on the side of the long box, this method of representation is more intuitive.

　　Relay use precautions.

 
　　1, rated operating voltage: refers to the relay coil voltage required for normal operation, that is, the control circuit control voltage. Voltage. Depending on the type of relay, it can be AC voltage or DC voltage.

 
　　2. DC resistance: The DC resistance of the coil in the relay, which can be measured with a multimeter.

 
　　3、Suction current: It is the minimum current that the relay can produce a suction action. In normal use, the given current must be slightly greater than the suction current, so that the relay can work stably. For the working voltage added to the coil, generally do not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burned.

 
　　4、Release current: This is the maximum current for the relay to produce release action. When the current of the relay in the suction state is reduced to a certain level, the relay will return to the unenergized release state. The current at this time is much less than the suction current.

 
　　Contact switching voltage and current: This is the voltage and current that the relay is allowed to load. It determines the size of the voltage and current that the relay can control, and cannot exceed this value when used, otherwise it is easy to damage the contacts of the relay.