Selection criteria for valve positioners

In many control applications, the valve positioner is one of the important accessories for adjusting the width, especially for a specific application, if you want to choose a suitable or excellent) valve positioner, you should pay attention to it. The following factors:
1. Can the valve positioner achieve "split ranging"? Is it easy and convenient to achieve split range? Having the "split range" function means that the valve positioner only has a certain range of input signals (eg: 4~ 12mA or 0.02-0.06MPaG) has a response. Therefore, if it can "split range", it can control two or more control valves successively with only one input signal contact according to actual needs.

2. Is the adjustment of zero and span easy and convenient? Can zero and span adjustments be done without opening the lid? But it's worth noting: sometimes in order to avoid incorrect (or illegal operation, this kind of arbitrary adjustment needs to be prohibited.

3. How stable is the zero point and span? If the zero and span are prone to drift with changes in temperature, vibration, time or input pressure, the valve positioner will need to be recalibrated frequently to ensure the correct stroke action of the regulating valve.

4. How accurate is the valve positioner? Ideally, in response to an input signal, the trim parts (Trim Parts, including valve core, valve stem, valve seat, etc.) of the regulating valve should be positioned exactly at the required position every time, regardless of the direction of travel or How much load the valve trims are subjected to.

5. What are the air quality requirements of the valve positioner? Since very few air supply devices can provide air that meets ISA standards (standards for air quality for instruments: ISA Standard F7.3), for pneumatic or electro-pneumatic) valve positioners, if they are to withstand The test of the real environment must be able to withstand a certain amount of dust, water vapor and oil pollution