Instrument valve signal conversion
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I have a question for all the experts here: When a signal is sent to the control valves via instruments, how does the locator convert this electrical signal into an appropriate amount of air flow? Is it related to a 4-20 mA current signal, and is there a proportional relationship between this current signal and the instrument air pressure of 0.5 MPa? How is the valve finally set in a fixed position? What proportional adjustments are available in it? I hope fellow sailors can give some guidance
It is the regulator that sends an electrical signal to the actuator; the actuator then converts this electrical signal into a pneumatic signal that drives the valve. This pneumatic signal is proportional to the electrical signal – for example, a 4–20mA electrical signal is converted into a pneumatic signal of 0.02–0.1 MPa to operate the valve.
The instrument air pressure is generally 0.5 MPa. Is 4 to 20 mA in a proportional relationship with this 0.5 MPa pressure?
Firstly, the electromagnetic converter is connected to the damper of the pneumatic amplifier; the lever principle is utilized here, with the 4-20mA current being converted into an attractive force exerted by the electromagnet. This force changes the stroke of the iron core, thereby altering the distance between the damper and the nozzle. Secondly, changes in this distance between the nozzle and the damper affect the flow control capacity of the pneumatic amplifier, which in turn controls the amount of air flowing into and out of the pneumatic control valve, thus regulating the opening degree of the valve.
Is the author referring to intelligent positioners or mechanical positioners? If it’s the latter, please check my first post for an explanation of the principle behind the YTC-1000R positioner