how does a DMM take a differential voltage measurement

[panfilero]

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!

 

[bw]

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.

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.

 

[Charles]

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.

It's hardly arbitrary when measuring a voltage drop across a component.

Generally, it's seldom arbitrary.

 

[Phil Allison]

"panfilero"

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.

** Try: www.aprilfool.com




...... Phil

 

[Charles]

So, what is the absolute voltage of Planet Earth?

Look here:
http://en.wikipedia.org/wiki/How_many_angels_can_stand_on_the_head_of_a_pin?

 

[Eeyore]

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?

Don't use the circuit common.

DMMs are differential measuring instruments by design.

Graham