How to select the 4-20ma range for position feedback
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Today, when checking the position feedback, the current of the valve as it went from open to closed ranged from 20–4 mA, before returning to 20 mA. Then the circuit board was sent away to have that potentiometer adjusted, and the current dropped from 20 to 16 mA. It took a long time of fiddling before I managed to get it to 4-20ma. I would like to ask everyone how to choose the correct range for 4-20ma? Then I took apart a unit that wasn’t in use before, removed the potentiometer wires, and measured the resistance. With each 90-degree rotation, the resistance decreases successively from 5.26 to 4.02, then to 2.72, and further to 1.227, before returning to 5.26. In the CW state, the resistances increase in sequence as they rotate clockwise. The CCW resistances decrease in order from largest to smallest.
This potentiometer rotates 360°. 1. During debugging, first find the position where it jumps from the maximum value to the minimum value, then rotate it 180° and note down that position. 2. Use this position as the midpoint for 4-20mA (12mA). 3. Turn the valve to the midpoint and secure the connection to the potentiometer. 4. The output for adjusting the valve on/off state is 4-20mA.
We use this in situ on control valves, allowing a 90-degree rotation from closed to open.
There is a fixed range of usage, and it needs to be determined through actual debugging