Control valves are used in process plants to control parameters like pressure, temperature, flow, and level within a required operating range to ensure product quality. For example, in an oil-gas separator, an operator would manually open and close a gas discharge valve to maintain the separator pressure at 70 psig by comparing the pressure gauge reading to the setpoint of 70 psig in their mind. This manual control can be replaced by an automatic pressure control valve (PCV) system using a pressure transmitter (PT) to read pressure and send the signal to a pressure indicator controller (PIC), which compares the PT reading to the user-inputted setpoint (SP) and then opens or closes the valve accordingly to achieve the setpoint.