What Is Process Control?
Process control systems refer to the ability to adjust and monitor a process in order to achieve the desired output. It is used by the industry to improve quality and performance.
A thermostat and heater can be used to control the temperature in a room. The thermostat will activate a heating source when the room temperature drops below the set point. At that point, the heater is turned off. This process continues as the room cools to maintain the desired temperature. The thermostat sets the temperature, and the heater adjusts to maintain the temperature. This is also known as on/off control or deadband control. This process uses a deadband, which is the difference in temperature between when the heater is turned on and when the set point is reached. This deadband keeps the heater’s temperature stable and prevents it from being switched on or off too often.
Complex Process Control Systems
A process control systems scenario where two fluids are mixed in a certain ratio would be an example. The flow of one fluid must increase while the flow of the other fluid has to decrease. Actuated valves are used to control the flow of both fluids. Based on the flow rate required, a controller calculates the flow that each valve will require. The PID controller will control each valve by adjusting the position of the valve based on the difference in the desired value (setpoint) and the measured flow rate. The controller will tell you how to open the valve to increase flow to the desired level if the flow measurement is too low. Many industrial processes are made up of smaller processes. Stability is essential for each process as unstable processes can cause instability in other processes. This instability is sometimes called variability.
Controlling close to the set point is important for most processes. This will help to reduce variability and increase the cost of the process. The set point must be increased to ensure that variability is minimized. This can often lead to wasted resources. If the flow rate is 10 gallons/minute to achieve the desired process control system result, and the variability is +/– 1 gpm then the set point would be 11gpm. This will ensure that the flow rate does not fall below 10gpm. The average flow rate of 1gpm becomes a wasted product. The operator could save the product if the variability were reduced to 0.1gpm.