Can the signals from several instruments control the same control valve?

Normally, a control valve is controlled by a signal output from only one instrument. This is because having multiple instruments output signals to control the same control valve simultaneously can lead to confusion and unpredictable results. Each instrument may have different measurement errors, sensor delays, or other factors, which can lead to variations in the signals output by the instruments. If multiple instrument output signals are connected directly to the same control valve, signal conflicts and inconsistencies may occur, making it impossible to predict the behavior of the control valve accurately. Therefore, to ensure the stability and reliability of the control system, generally only one instrument output signal is used to control a control valve. If multiple instruments need to be controlled together, a distributed control system is generally used, or controllers are employed for signal processing and coordination. Through the controller, multiple instrument output signals can be integrated and weighted, before the final control signal is sent to the control valve to achieve precise control of the valve. .

A control valve can receive only one signal; multiple signals either have one of them selected through certain selection logic, or they are combined into a single signal through some calculation.

Selective control systems can be considered as such; for example, an automatic selective control system for the peak temperature of a reactor. Multiple temperature sensors installed at different locations in the reactor’s catalyst layer send their signals to a maximum value selector, which then selects the signal corresponding to the highest temperature and uses it to control a control valve.

Not all complex controls involve multi-variable control of a single valve; there is also point-type cascade control, with primary and secondary variables as well as primary and secondary loops