The valve positioner is one of the important accessories for the control valve, so there are several factors to consider when choosing a suitable positioner.

1. Can the positioner achieve "Split_ranging"?

If the positioner can "Split_ranging" that the positioner only responds to a certain range of the input signal (such as 4~20mA or 0.2~1.0bar), the positioner can set one input signal contact to control two or more than two controls

2. Is it easy and convenient to adjust the zero and span?

Some positioners can adjust the zero and span without opening the cover, but in order to avoid incorrect or illegal operation, this method of random adjustment should be used cautiously or prohibited.

3. What is the stability of the zero and span?

If it is easy to drift with changes in temperature, vibration, time or input pressure, it needs to be constantly adjusted by the center to ensure that the stroke of the control valve is accurate.

4. How accuracy of the positioner?

Ideally, for each input signal, the internal components of the control valve (Trim Parts, including the valve plug, stem, seat, etc.) should be accurately positioned at the desired position each time, regardless of the direction of travel or how much load the internals of the control valve are subjected to

5. The positioner's requirements for air quality?

Since only a very small number of air supply units can provide air that meets the requirements of the ISA standard (the standard for instrument air quality), pneumatic valve positioners must withstand a certain amount of dust, moisture and water to withstand the test of the real environment. Oil pollution, etc.