When the manual operator, PID regulator, DCS or PLC adopts pneumatic control valve to complete the process control, it is necessary to convert the electrical signal into a pneumatic signal to control the work of the pneumatic actuator. There are electrical converters and electrical valve positioners that meet this function, but because the structures and functions of these two meters are different, there are also differences in the use of electrical converters and electrical valve positioners.

one. Electrical converter

The input current signal of the electrical converter is proportional to the output pressure signal. That is, when the input signal changes from 4-20mA, the output pressure of the electrical converter also changes from 20-100kPa, thereby converting the current signal into a pressure signal. The electrical converter is equivalent to a 1:1 amplifier, except that it receives electrical signals. Since there is no mechanical connection between the electric converter and the regulating valve, it has the advantages of lower price, convenient installation, debugging and maintenance than the electric valve positioner. Therefore, the electric converter should be preferentially used under the same conditions.

The electrical converter is directly installed on the pneumatic control valve for use, without the need to install a feedback lever, but because there is no feedback link, it cannot be a closed-loop control system, and the control accuracy is very problematic, and it is rarely used alone! Usually, the electric converter must be used in conjunction with the pneumatic positioner to realize the accurate positioning of the valve.

2. Electric valve positioner

Electric valve positioner is actually a combination of electrical converter and valve positioner functions. Therefore, the function and role of the electric valve positioner have been further expanded. For example, it can be used to improve the linearity of the valve position; because it can overcome the friction of the valve stem and eliminate the influence of the unbalanced force of the regulating valve, it is very suitable for high-pressure media and Application in high pressure difference occasions; application in large-diameter control valves; application in high and low temperature medium control valves; also can be used in fast adjustment occasions, where you want to improve the flow characteristics of the control valve.