For the electrical positioner of pneumatic control valves
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I have connected only one 2*1.5 4–20mA cable to the pneumatic control valve; can my control room then see the opening degree of this valve?
Pneumatic control valves generally do not have a position feedback signal, so they cannot directly indicate the valve’s opening degree. However, during calibration, the valve operates based on the input signal: 4 mA corresponds to 0% or 100% of the valve’s range, 20 mA corresponds to 100% or 0%, and 12 mA corresponds to 50% of the valve’s range. If the control valve is calibrated accurately, its position can be determined from the output of the controller.
To view the actual valve position of the control valve, a valve position transmitter also needs to be installed. Generally, valve position transmitters are rarely used to indicate the valve position; instead, the valve position is usually indicated indirectly through the output signals of a DCS or regulator. As long as the valve position of the control valve is accurately calibrated, there should be no problems.
It is possible to check the valve opening angle; for that, there needs to be a feedback mechanism on the actuator, or a feedback device for the valve opening angle can be installed. This is used only for analog signals; if it’s a bus-type system, then it’s sufficient as long as the actuator supports it
Your valve positioner is electrical; in other words, it’s of the mechanical type used in the past. To obtain feedback signals from the valve, an external valve position feedback device is required, and the DCS needs to have AI points added. For positioning purposes, a position switch is needed, which represents a DI point.
The opening degree can be seen. But that’s just the degree of your output. You don’t know the actual opening degree. If the valve is important, a feedback device must be installed, as well as another set of cables for transmission. Everyone upstairs is talking nonsense; it’s impossible to know the opening degree with just one set of cables.
No, you can only determine the signal applied to the control valve, but you cannot know its actual opening degree. A feedback signal also needs to be connected