Changing ground reference

Projects General Guidance
1

Is there a way to have a different ground than your voltage source? I ask because I want to do the following:

There is a pressure transducer at work that has 2 lines going to it. Those lines can range from 17-22V (nearly always at 19-21) throughout the entire pressure range. I want to be able to tap into those 2 lines to get my own pressure data. Since this is a 5V difference I was thinking about regulating the V down to 17V consistently and using that as a reference and then measure the Vdiff. Does this work?

The other option I can think of is to use a divider to bring down the 22v max to 5v but I lose a lot of resolution that way

2

That's not practical to do - use a voltage divider. If you need to keep the resolution, an appropriate opamp could be used.

3

Yes and No.

Can your project be battery-powered? Then it can float at whatever potential it's attached to. But you can't then plug anything else into it to see the data, like your computer, unless that is also battery-powered and not connected to anything else.

Your regular 5V power bricks are isolated - the 0V wire can be any voltage with respect to Earth. (Keep it less than the power line voltage though.) That will let your device be powered without a battery but it still can't be connected to anything else.

If you really need to connect this to something which isn't isolated, such as a PC to display the data, then there are communication standards which isolate the voltage but still transmit data. You can make an adapter yourself for basic Serial communication with two opto-isolators. (And it's easy to buy two in the same chip.)

Alternatively, look for an A-D converter chip which does allow 20V "common mode voltage" on its pins. They do exist, but they are not usually found in Arduino hobby shops.

4

Circuit diagram?

5

I guess I don't HAVE to have it connected, but it really would be nice.

I was also thinking this sounds like opamp territory, but I don't really know much about the with regards to proper specs, wiring

Basically do you powet it with 0-5 creating the limits and then have 17-22 as input voltage?? (Pic attached)

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6

That diagram is a good concept. But most opamps can't cope with common-mode voltages that are outside their supply voltage. (And most Opamps can't be powered with more than 30V.) They're not actually isolating - the two circuits are still electrically connected.

If you can power the Opamp from 24-30V from the source machine and you can also power the 5V Arduino from that same input then you are well on the way to making this work.

7

What kind of transducer uses a 17 to 22 volt range? Seriously doubt it. I’d be more inclined to think the transducer is a 0-20 or 4-20 ma current loop device. If so, the absolute voltage means nothing.

Look a part number on the device and do some research.

8

Enjin:
There is a pressure transducer at work that has 2 lines going to it.

Can you demystify this mystery device? Then at least we know what we're actually talking about and all the guesswork can be kept at a minimum.