Relay is an automatic switching element with isolation function, widely used in remote control, telemetry, communication, automatic control, electromechanical integration and power electronic equipment, is one of the most important control components. Relay generally have can reflect a certain input variable (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.) induction mechanism (input part); There is an actuator (output part) that can realize the "on" and "off" control of the controlled circuit between the input part and the output part of the relay, and an intermediate mechanism (drive part) that coupling the input, function processing and drives the output part. As a control element, in general, the relay has the following functions: 1) expand the control range. For example, when the control s