# Wireless Voltmeter probes?

Discussion in 'General Electronics Discussion' started by SPDUK, Dec 16, 2014.

1. ### SPDUK

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Dec 16, 2014
Hey everyone! glad to be a new member on this site.

Ok so I understand that by definition voltage implies two locations and therefore Voltage from one point doesn't make sense. Would it be possible to build a voltmeter that had two separate wireless probes. They would each measure a signal and then send it to the voltmeter to subtract the difference?

I realize that it may be impossible and not make any sense.

Is there such thing as a simulated ground that can be used as a reference for each probe and subtracted later on to give you just the difference between the two probe points? Would that even give you a correct voltage measurement?

I'm sorry, if this doesn't make sense I'll do my best to clarify if needed. Thanks a lot!

2. ### Gryd3

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Jun 25, 2014
Won't work this way... as electricity needs a current path.
Only one probe won't cut it, as the electronics inside your 'wireless' probe won't be able to determine what the voltage is at the tip without being able to compare it to something.

If we threw you in space, would you know how fast you're going? You could be in radio contact with someone and be completely unsure, because there is no reference for you to see to guess or calculate your own velocity.

So. each probe would need it's own ground, or each probe would need to be tethered to the other.

davenn likes this.
3. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
I'm not sure what you mean by "wireless probes". If you're asking if a voltage measurement can be transmitted and read by a remote receiver then the answer is absolutely yes. As for "single probe" measurement .... Not on this world or for that matter, not in Space either.

Arouse1973 likes this.
4. ### BobK

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Jan 5, 2010
I have to disagree with the other posters. If there is a common ground between the two circuits, it could be done. In this case you would be reading each voltage WRT ground, then subtracting them to get the voltage WRT each other.

Bob

5. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Bob,
Perhaps I shouldn't have used the term "probes". Whether or not there's physical probes voltage is measured between two points. As in spice simulators voltage pins are measuring from ground reference; while voltmeter probes can measure between any two nodes.

6. ### BobK

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Jan 5, 2010
Yes, I understand. My point was that under some conditions, i.e. having a common ground, the voltage between the two points can be measured without putting the two probes of the measuring device on the two points, but rather by making a separate measurement between each of them and the common ground.

Bob

7. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Bob, I thought I understood your point but now I see I didn't. Yes, Roger that.

Chris

8. ### BobK

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Jan 5, 2010
Hey Chris,

Haven't seen you in a while. Welcome back!

Bob

9. ### SPDUK

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Dec 16, 2014
"Not on this world or for that matter, not in Space either." haha thanks guys."

Bob, so I get that as long as lets call it v1 and v2 are with respect to the same ground you can subtract v1 and v2 to get the voltage between those point.

So I guess my question now is can the ground reference signal be generated. If I attached each of the seprate grounds (that should be conneced) with a reciever and transmitted an identical signal to both of them or instead of transmiting a signal having two of the exact same Batteries as a ground reference, would that work?

10. ### Gryd3

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Jun 25, 2014
That is the part that you cannot do. You cannot form a virtual radio ground that would be common between the probes as far as I know.
Remember you need current flow to be able to measure voltage with your probe.
The problem is in the individual probe, not the fact that you want two wireless probes.
If the individual probe only has one contact, it has no way of knowing what voltage that contact is touching.
You may be able to get away with something that will partially measure certain AC voltages, but DC will be completely out of the question.
Here's a question for you: What is your current elevation?
-Do you answer based on your distance from the floor or ground outside?
-Or do you answer based on Sea level? (What if there was no Sea?)

11. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Hi Bob,
Thanks for the welcome back.
Chris