Design of automatic control instrument systems: The role of electro-pneumatic converters and electro-pneumatic valve positioners in control systems

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This post was last edited by lilyqiu on 2019-4-11 21:45. Knowledge sharing: The role of electro-pneumatic converters and electro-pneumatic valve positioners in control systems. In process control systems, regulators are often electric, while actuators (control valves) are usually pneumatic; therefore, it is necessary to convert electrical signals into pneumatic signals in order to use them with pneumatic actuators. An electro-pneumatic converter is a device that converts electrical signals into corresponding pneumatic signals. In control systems, if the controller used is an electric controller whose output signal is 0–10 mmA DC or 4–20 mmA DC, and the actuator chosen is a pneumatic actuator whose input signal is typically 20–100 kPa, then an electro-pneumatic converter is necessary to convert the electrical output signal from the controller into the corresponding pneumatic signal, so that it can be accepted by the pneumatic actuator. However, in practical applications, it is rare for the signal output of an electro-pneumatic converter to be used directly to control a control valve via a pneumatic actuator, as electro-pneumatic converters lack positioning functionality. When pipeline pressure acts on the valve core and pushes the valve stem, the electro-pneumatic converter is unable to counteract this pressure and will deviate from the position required by the control valve. This article was first published on the WeChat official account “Automatic Control Academy”. For example: the electro-pneumatic converter outputs a 50% signal to the pneumatic actuator, which should therefore be at 50% of its travel distance. However, due to the inability to overcome the pressure in the pipes, the pneumatic actuator deviates from this 50% position, resulting in large errors in the control valve and reduced precision of regulation. In certain specific locations, combining electric-to-pneumatic converters with pneumatic valve positioners enables the control of pneumatic actuators. In addition to converting electrical signals into pneumatic signals, the electro-pneumatic valve positioner also ensures that the displacement of the valve stem is in a linear relationship with the magnitude of the input signal; this allows for accurate determination of the relationship between the input signal from the controller and the valve position. By combining electrical conversion functions with valve positioning capabilities, it is called an electro-pneumatic valve positioner, and it is widely used in practical engineering applications.