Devices strategically placed along your process to accurately measure variables such as position, temperature, pressure, level, flow, vibration or chemical composition. They may output discrete, analog or serial communication signals to the controller. There are many different types of instruments available today, some accurate within a half percent of their measured value. Other instruments allow contactless measurement of your process material and easy retrofitting onto existing systems.

The “brain” of your control system which receives data from the instruments, interprets the data and generates output signals to control the actuators. For larger systems with many instruments, a Programmable Logic Controller (PLC) is often used as a flexible and powerful process controller. Many instrument suppliers can also provide a specialized microcontroller for use in smaller processes where only basic functionality required.

These are devices capable of modulating the process parameters. They may consist of motor operated valves, gates, fans or pumps. Equipment such as heaters and ultraviolet purifiers also fall under this category of process modulating devices. As they receive commands from the controller, actuators change the state of process variables and when the instruments report this change, a feedback loop is created.

Often referred to as the “top-end” of your control system, the operator interface allows for interaction between people and process. Nowadays, computer monitors or touchscreens uploaded with special software act as powerful Human-Machine Interfaces (HMIs). More traditionally, push buttons, switches, adjustable knobs and indication lights also serve as components of a reliable operator interface.  A well-designed operator interface will succinctly display the important components of your process and allow operators to adjust setpoints or manually control system actuators within the safe limits of the system.