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The Difference Between Electrical Converters and Electrical Valve Positioners
Release time:
2026-04-07 15:22
When manual operators, PID controllers, DCS systems, or PLCs use pneumatic control valves to perform process control, it is necessary to convert electrical signals into pneumatic signals in order to operate the pneumatic actuators. Electrical transducers and electric valve positioners both serve this function; however, because these two types of instruments differ in structure and function, their applications also vary.
1. Electrical Converter
The input current signal of the electrical transducer is proportional to the output pressure signal. Specifically, as the input signal varies from 4 to 20 mA, the output pressure of the transducer varies from 20 to 100 kPa, thereby converting the electrical current signal into a pneumatic pressure signal. The electrical transducer functions essentially as a 1:1 amplifier, except that it receives an electrical signal rather than a mechanical one. Since the electrical transducer is not mechanically connected to the control valve, it offers advantages over electric valve positioners, including lower cost and greater ease of installation, commissioning, and maintenance. Therefore, under identical conditions, the electrical transducer should be given priority.
Electrical transducers are installed directly on pneumatic control valves for operation; no feedback linkage is required. However, since there is no feedback loop, the system cannot function as a closed-loop control system, resulting in significant limitations in control accuracy, and such configurations are rarely used independently. Typically, electrical transducers are paired with pneumatic positioners to achieve precise valve positioning.
2. Electrical Valve Positioner
An electric valve positioner is essentially a combination of an electrical-to-pneumatic transducer and a valve positioner. As a result, its functions and applications have been further expanded: it can be used to improve the linearity of valve positioning; because it can overcome stem friction and eliminate the effects of unbalanced forces in control valves, it is particularly well suited for use with high-pressure media and large pressure differentials; it is also applicable to large-diameter control valves and to control valves handling high- and low-temperature media; moreover, it can be employed in fast-response control applications and in situations where it is necessary to enhance the flow characteristics of the control valve.
2020-01-19
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