Calculation of the relationship between valve opening degree and current for equal percentage valves
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I would like to ask if anyone knows how to calculate the relationship between current and valve position for pneumatic control valves with equal percentage characteristics That is, what valve positions do 4.8.12.16.20 mA correspond to respectively? Is it also related to different percentage equivalents?
This post was last edited by jlshnlhj on 2018-10-23 09:32. It’s already specified that it’s a percentage-based feature; as long as the signal range is 4-20mA, just do the calculation and that’s it.
Do not confuse the flow characteristics of the control valve with its position relationship. That is, for proportional control valves, the valve position is in a logarithmic relationship with the flow rate passing through the valve, while the 4-20MA current is in a linear relationship with the valve position; you can perform the conversion yourself.
Equal percentage refers to the flow characteristic of the valve, while valve position feedback refers to the degree of opening of the valve; valve position feedback and flow characteristic are two distinct concepts. The valve position feedback current output is linearly related to the valve opening degree; values of 4mA, 8mA, 12mA, 16mA, and 20mA for the valve position feedback current correspond to valve openings of 0%, 25%, 50%, 75%, and 100% respectively. Changhui Instruments: yunrun.com.cn
It should be the relationship between relative flow rate and the relative opening degree of the valve. Equal percentages represent a logarithmic relationship.
The person who answered correctly upstairs is right; the percentage in question refers to the relationship between opening degree and flow rate
Thank you to everyone who replied above; I agree that the percentage corresponding to the valve position is related to the flow-rate and opening degree. However, from the information I’ve gathered, the relationship between current and valve position is not linear. Moreover, for one of our valves, the corresponding values are also non-linear: 4-0, 8-12.5, 12-25, 16-75, 20-100.
The relationship for valves on our side is also nonlinear; specifically, it’s 4-0, 8-12.5, 12-25, 16-75, 20-100. What’s the reason for this? Is the stroke-current relationship of equal percentage valves necessarily linear?