Hello

What's the relevance between frequency inverter, relay and PLC?

The inverter can be controlled by PLC.
Also can control the frequency inverter by the PLC through the relay contact points.
And also can control the inverter by relay to achieve multi-speed step operation.

The relay usually composed by the iron core, coil, armature and contact spring etc. As long as there is a certain voltage on both ends of the coil, the coil will flow through a certain current, thereby generating electromagnetic effects, the armature will be attracted to the core in the attractive interaction of the electromagnetic force to overcome the return spring tension, so to drive the armature dynamic contact with stationary contacts (normally open contact) pull. Electromagnetic suction disappears when the coil is de-energized, the armature will return to its original position in the reaction force of the spring, and release of the dynamic contact with stationary contacts (normally closed contacts). This pull and release, so as to achieve conduction in the circuit for cutting purposes.

The inverter is the power semiconductor devices by frequency power conversion for another frequency energy control device, can achieve the soft starter for AC induction motor, variable frequency control, improve running accuracy, change the power factor, over current / over voltage / overload protection and other functions.

PLC programmable logic controller, a digital computing operation of electronic systems, designed for applications in industrial environments designed. It uses a programmable memory for internal storage program, the implementation of logical, sequential control, timing, counting and arithmetic operations such as user-oriented instruction and all types through digital or analog input / output control machinery or production process. It's the core part of the industrial control.

Relay is executive component to connect the electric drive circuit, automatic control circuit. The output terminals of the inverter and PLC use it a lot.

The inverter is a motor-driven power supply, generally it converts AC into DC current first, then change DC current into adjustable frequency and voltage power, and this "adjustable" process is very meticulous, intelligent, the PLC system with be able to complete many general AC motor is unable to complete the smooth speed, constant torque, torque adjustment and other functions. Its internal smart chip that can store and modify established procedures, acceptance and implementation of the directive.

PLC is a super industrial computer via an interface circuit, it can be connect inverter, monitor, measure, alarm, drive circuit easily, and automatic control, monitoring, remote control, telemetry, remote adjustment. Its interface circuit, the switching circuit many also use a relay to execute the instruction.

First should understand the principle and function:
1. Relay depends on coil on/off circuit
2. Inverter is used to change the frequency
3. PLC is strong controller according to the input control output.