For the "normally open and normally closed" contacts of the electromagnetic relay, it can be distinguished as follows: the static contacts in the disconnected state when the relay coil is not energized are called "normally open contacts"; Static contacts in the on state are called "normally closed contacts". Relay generally has two strands of circuit, low voltage control circuit and high voltage working circuit. The relay has the following functions: 1. Expand the control range: for example, when the control signal of the multi-contact relay module reaches a certain value, it can change, open and turn on the multi-channel circuit at the same time according to the different forms of the contact relay module point group. 2. Amplification: for example, sensitive relays, intermediate relays, etc., with a very small amount of control, can control a large power circuit. 3. Synthesis signal: for example, when multiple control signals are input into the multi-winding relay in the prescribed form, the predetermined control effect is achieved after comparison and synthesis. 4. Automatic, remote control, monitoring: for example, the relay on the automatic device, together with other electrical appliances, can form a program control line, so as to realize automatic operation.