Discussion on FO valves
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Recently, there has been a problem: with the FO control valve equipped with an intelligent positioner, it remains fully open when both the air supply and the signal line are disconnected. This is normal behavior. But once the signal wire is connected (with a current of about 4 milliamps), the valve closes completely. Shouldn’t it shut off completely only when there is a 20 milliampere current signal? (I remember that mechanical positioners shut off completely at a 20 milliampere signal.) It’s a new valve; the smart locator has not changed the direction of the signal input.
It’s a problem with the system; the system air shut-off valve in the central control unit has a range of 0 to 100%, which corresponds to 20 to 4 mA. Try using a signal generator to see if the same phenomenon occurs
Don’t overthink it; just solve the problem. If it can’t be solved or the situation keeps improving and worsening, replace it as soon as possible
Don’t overthink it; just solve the problem. If it can’t be solved or the situation keeps improving and worsening, replace it as soon as possible
Smart positioners can have forward and reverse actions set. Study hard*.
In this control loop, if the control parameter (such as T) increases, does the process require the valve to be opened more or closed?
The current status of the locator is that 4 mA corresponds to valve position 0, while 20 mA corresponds to valve position 100; the forward and reverse action of the locator can be adjusted accordingly
This is probably due to an inversion on the control side; have them make the change there
Issues with the settings of the intelligent locator: changing the direction of signal input
What else can one do? That’s a question even vocational school students wouldn’t ask.