Valve Position Indication


Thread Starter


Is there any way to show indication to show valve opening (as GREEN LED) and closing (as RED LED) from 4-20mA output which is coming from Valve positioner , I mean drive 2 LEDS.
If you don't have /can't use some intelligence to provide digital outputs based on limits you set, you could solder-up your own little op-amp circuit, or you could do probably the best thing, and put proximity sensors at the valve and run the wires back to where you need the indication, driving 2 LEDs. If you want to try the op-amp idea, I can halp via email.

Hall, Christopher W


I assume that what you want to do is to have the RED LED on when the valve is closed (i.e. when the positioner says it is less than say X% open) and the GREEN LED on when the positioner says the valve is more than Y% open. You could do this using any proprietry two channel trip amplifier of which there are a number on the market.

Chris Hall, Control Engineer

Johan Bengtsson

Well, driving two LED:s should be possible, especially if you don't require more current thru the led than about 2-3mA (some leds will probably be bright enough by this small current) and
accept a voltage drop around 2.5-3V. You will not (by your description) drive more than one led at a time, that is what counts, not how many leds the assembly have.

If you require higher current you have to make a DC-DC converter and accept a higher voltage drop, especially at low loop currents. This would be more tricky since introducing a DC-DC converter
feeding from the loop most surely will indroduce noice you rather be without and in the end it would probably be easier to just feed the circuit externally.

/Johan Bengtsson

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