Action and reaction
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Everyone, PIC005b is set to reactive mode and the valve is set to FO – is this configuration correct?
This post was last edited by ylb913 on 2018-8-5 at 19:49. The diagram PIC005b is used to control the pressure at the rear; it turns on when the pressure there is low and turns off when the pressure is high. This is what is known as \"reaction,\" and it seems to make sense. From this perspective, there’s nothing wrong with FO either. Fault open, pressure after the pressure relief valve.
But when the pressure is low, the controller output increases. The actual opening degree of the air shut-off valve has decreased
This post was last edited by ylb913 on 2018-8-4 at 23:04. 1. The direct and reverse actions of the control mechanism (control valve structure) will be disregarded; only the direct action will be considered. 2. Then, it’s time to consider the positive and negative actions of the remaining actuators (diaphragm heads, cylinders). When the signal increases, the push rod moves downward, resulting in a positive action (instrument air enters from above the diaphragm head, with the spring below, FO); otherwise, it is a negative action (instrument air enters from below the diaphragm head, with the spring above, FC). 3. This control valve regulates the pressure downstream of the valve; when the FO pressure is low, the valve should be opened, and the output from the air-operated valve controller should decrease. 4. From the above reasoning, FO can only be of positive action. 5. It seems that the positive and negative effects mentioned here include one additional factor, namely the difference between the pressure behind the control valve and the pressure in front of it; the pressure in front of the control valve is considered positive, while the pressure behind it is considered negative.
Is e-1129 a heat exchanger? Medium-pressure steam enters and exits on the left side; what comes out on the right side also appears to be steam, and it has to mix with the steam that has been cooled and depressurized. What is the purpose of such a design?
If the valve is FO, then it should be set to direct action here.
For ordinary control valves, during commissioning it is required that the DCS set the opening degree to 0~100%, which corresponds to the actual 0~100% opening degree of the valve. For valves in FO format, the control signal is generally 20~4 mA, with the regulator set to reverse action. If the control signal is 4~20mA, set the regulator to positive action.
Stop being an idiot; controllers have feedback.