Hydraulics and Pneumatics

Chapter | seven. Process Control Pneumatics

If some industrial process is to be automatically controlled, there will be many process variables (e.g. temperature, flow, pressure, level) which need to be measured and kept at the correct value for safety and economical operation. In Figure 7.1, for example, water flow in a pipe is to be kept at some preset value.

Figure 7.1 Closed loop control

In Figure 7.1 the flow is measured to give the current value (usually termed PV for process variable). This is compared with the required flow (called SP for set point) to give an error signal, which is passed to a controller. This adjusts the actuator drive signal ...