I've been trying to find some info on this on google... but I just keep finding sites on DMM and how to measure voltage with them... but my question is... how does a DMM manage to read a voltage without access to the common point of the circuit your measuring?
If anyone knows of a good website that explains that could you please point me towards that... I can't find one.
Thanks!
A voltage is a potential difference between two points. All voltage measurements are from point A to point B. On a DMM the voltage is from probe tip to probe tip. It helps to have good probes.
It's like a tape measure; it measures the distance (voltage) between any two points. And like a tape measure, there's no available "zero" point to make absolute measurements from. We sometimes use a chassis, or the earth itself as "ground", but that's still arbitrary.
John
It's hardly arbitrary when measuring a voltage drop across a component.
Generally, it's seldom arbitrary.
So, what is the absolute voltage of Planet Earth?
John
"panfilero"
** Try:..... Phil
Look here:
Never give up hope!
Merely count the number of protons in the earth, and subtract the number of electrons.
Multiply that by 1.6e-19 to get the net charge on the planet, in colombs.
Divide by 708e-6, the capacitance of Earth in farads.
And there you are.
ftp://jjlarkin.lmi.net/Exit201.jpg
John
Don't use the circuit common.
DMMs are differential measuring instruments by design.
Graham
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