Relay is a kind of electrical control device, is when the input (excitation) changes to meet the specified requirements, in the electrical output circuit to make the controlled amount of a predetermined step change of an electrical appliance. It has an interaction between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in automatic control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit. Industrial general relay products are widely used in various fields of national economy because of their particularity. Including the project market: metallurgy, electric power, petrochemical, transmission and distribution, building and other project markets, at the same time in the OEM market, such as textile machinery, rubber machinery, lifting machinery each single equipment has the application of industrial general relay. So the relay has an important basic position in the national economy. The development of relay industry of our country starts in 20th century 50 early years. In order to meet the production needs of national defense and military industry, some complete machine factories began to engage in the production of relay products. In 1958, the domestic relay professional factory state-owned 792 factory was born. After 50 years of development, the relay industry in our country develops rapidly, at present, there are nearly 400 various kinds of relay manufacturers in our country, relay enterprises are generally small in scale, only a small part of enterprises have the production capacity of high-end relay, the average sales of each enterprise is only 70 million yuan. At present our country has hundreds of relay enterprises, most of them are in the production of low-cost electromagnetic relay, only a small part of enterprises are expanding the production scale of high-end electromagnetic relay. Relay production capacity in our country is constantly improving, the pace of innovation is accelerating, and constantly strengthening international competitiveness, whether industrial or enterprise level, have a certain competitive strength, our country has entered the relay industry big country ranks in the world