# analog pressure gauge to 4 to 20mA

1. ## analog pressure gauge to 4 to 20mA

Hi,

I have a analog pressure gauge of range 0 to 10bar. Is it possible to provide output of 4 to 20mA. I just want to try it. But don't know how to convert the mechanical to electrical output signal.

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I assume, a magnet can be attached to the pointer shaft of pressure gauge. When the pressure is applied, the magnet on the pointer shaft rotates proportionally to the instrument pointer linearly.

This can be detected. Am I right? What sensor or IC is to be used?

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2. ## Re: analog pressure gauge to 4 to 20mA

A lot depends on the travel distance of the pointer.

By mounting a tiny strong magnet on it, its position may be detected by a hall sensor. To get linear response needs lots of experimentation and adjustments.

Optical detection is feasible. Possibly by cutting a paper disc which you glue to the pointer. The disc is painted (or shaped) so it changes light exposure on a photosensor.

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3. ## Re: analog pressure gauge to 4 to 20mA

We have no idea what size the pressure gauge is but if we assume it is a standard rotary type with a moving pointer, my approach would be to remove the pointer and replace it with a transparent plastic disc. On the disc I would print (preferably using a laser printer rather than inkjet) a long curved arrow near the outer edge. Then a fixed LED light source and photosensor (an LDR perhaps) would pick up light passing between them but through the arrow. As it rotates, the width of the arrow would obscure more or less light and give you a proportional reading. You still have to convert that to 4-20mA if necessary but that is fairly simple to do electronically.

If the idea seems practical, you could consider using a different pattern printed on the disc and more sensors to give a direct digital output. You can still convert that to 4-20mA but it becomes more versatile. Research "optical encoders" for ideas and remember laser printing and OHP transparent film is quite cheap these days.

Brian.

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4. ## Re: analog pressure gauge to 4 to 20mA

Brilliant suggestion, Brian.

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