Analog output signal means signals continuously transmitted from control room (PLC/DCS) to local control panels, field instruments such as control valves.
Electric operated valves and regulating valves for controlling pressure of pipe, and VFD for controlling frequency of aerators or pumps, etc., are typical examples, which are controlled by analog output signals. More specifically, there are electromagnetic valves and regulating valves used to control pressure in the piping.
There are also aeration blowers or VFD (inverter) equipment used to control pump speed (rpm). One of the transmission systems for analog output signal connects directly to the I/O device of PLC/DCS via shielded cables.