Understanding the process control loop
The process control loop is a set of devices and tools designed to maintain the desired output from a process variable. Control loop components and instruments measure the variable, respond to it, and control it to maintain a setpoint.
A control loop system can be either an open-loop or closed-loop system, which we explained in an earlier section of this chapter. It usually consists of a sensor or transmitter, a controller, and an actuator. The following figure shows a process control loop for level control:
Figure 12.16 – The process control loop for level control
The process control loop in the preceding figure is explained briefly as follows: the pump supplies water to the tank and a control valve (the final control element) controls the flow rate depending on what it learns about the tank level through the signal it receives from the level controller, which has a setpoint. The level transmitter provides...