Regarding valve positioners

Its function is to directly convert the 4–20mA signals sent from DCS/PLC into gas signals

Valve positioners include pneumatic valve positioners, in which the input signal is a pneumatic signal and a pneumatic signal is output to the control valve; these are now rarely used； The second type is known as an electric/pneumatic (electric) valve positioner, which accepts a 4-20mA current signal as input and outputs a pneumatic signal to control the control valve.

To understand this, you first need to know what a standard gas signal is. An electric valve actuator is also known as an electrical converter, but the gas signal it generates is not a standard gas signal; it is merely driving gas.

Oh, senior, but I just checked – the description of an electric-pneumatic valve positioner is that it converts the electrical analog signal of 4~20mA coming from the regulator into the corresponding pneumatic signal of 20~100kPa or 40~200kPa, which is then used to drive the pneumatic actuator. I also would like to ask, what exactly does this regulator refer to? I checked, and the standard gas signal is also 20~100 kPa. Very confused

It’s not easy to explain this – a valve is essentially a pneumatic actuator. But... in simple terms, an actuator includes anything that serves to regulate processes, including valves; it’s also referred to as an actuating mechanism, and it is a device that enables the valve to move, comprising components such as cylinders, rods, and valve spools. A pneumatic signal is a standard signal; in some cases, pneumatic signals are used to control actuators. However, just because a pneumatic signal can control an actuator, it does not necessarily mean it can control the entire actuation mechanism, as different actuation mechanisms have varying specifications and require different levels of force. Therefore, the valve positioner simply converts electrical signals into pneumatic pressure that is applied to the actuator; it is not a standard pneumatic signal. Of course, there are also valves driven by pneumatic signals. Currently, there are two ways to control actuators: via pneumatic signals or electrical signals.

This post was last edited by FightingNow on 2016-3-14 at 19:01. Nowadays, all locators are intelligent! ! It’s not necessary to convert it into a standard gas signal as you said! The input signal for intelligent electrical valve positioners is a standard 4–20mA or 1–5V electrical signal, which must be converted from analog to digital form before it can be used as an input signal for the microprocessor. After analog-to-digital conversion, the output signal is digital; it is usually sent to a piezoelectric valve assembly, and the opening and closing of this valve assembly is used to regulate the air pressure acting on the diaphragm of the control valve. In contrast, the output signal from a conventional electrical valve positioner is an air signal that has been amplified by a pneumatic amplifier! As you said, things like the old nozzle damper valve positioners… that’s all there is now; microprocessors are available!

Intelligent ones are not needed! ! Previously, valve positioners were supposed to convert standard electrical signals into standard pneumatic signals, which were then amplified by a pneumatic amplifier! ! ! It should be like this