In production or manufacturing industries, most of the processes are made to run automatically with less human intervention for better rate of production, efficiency, safety and reliable operations.

  To make these operations work automatically we need various instruments connected in a certain way, and these instruments often consist of sensors, controllers, actuators and monitoring devices. The image shown below will give you a little idea on how these instruments are connected.

Let us divide the system into some areas


  • Field devices
  • Controller Units
  • Monitoring and controlling equipment


Field Devices:-

                In the field where the processes are happening, there are various devices used for sensing and controlling the operations. Sensors give the feedback to the controller. Sensors are used to detect events or changes in temperature, pressure, level and proximity, and most parameters are conditioned to interface with controllers using devices known as transmitters.

Controllers give the output according to user defined conditions. Output devices generally called as Actuators, comprises of motors, solenoid valves, current to pressure convertors, indicators, heaters and so on.

Controller Units:-

                Controller Units are often placed in control panels. Some types of controllers include PLC, DCS, VFD, servo drives etc. Programmable Logic Controllers (PLC) are programmed to perform certain tasks based on the inputs provided by field devices which are connected to the controller either remotely or locally by field communication protocols and field cables respectively.

                VFDs and servo drives are used to control the motor parameters like speed, direction, torque etc. These devices can be controlled using an external controller like PLC.

Monitoring and Controlling Equipment:-

                In a large production plant, the operations are monitored and controlled remotely by SCADA and HMI systems. Controllers are connected to computers in which the visualisation of the plant is created by SCADA applications. It adds the necessary safety by monitoring and controlling the operations remotely. HMI and SCADA have many features like alarming, security, recipe management and data logging which enables further optimisation of the process by analysing the acquired data via SCADA software.