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max
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 « on: July 04, 2010, 12:28:41 12:28 »

Hi friends,

How to measure part of a voltage with ground reference?

e.g  I want to measure voltage from 10v to 14v with ground
reference (i.e 0 - 4v ref to ground), which is varying from 0 to 20v.

Regards
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pickit2
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 « Reply #1 on: July 04, 2010, 12:43:14 12:43 »

http://english.cxem.net/izmer/measured44.php

shows you how
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Biggles
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 « Reply #2 on: July 04, 2010, 12:46:56 12:46 »

I have never had to do this, I think your answer is in opamps to subtract voltage.. something like this...

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bobcat1
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 « Reply #3 on: July 10, 2010, 03:01:23 15:01 »

Hi

You need to use a resistive voltage divider using 2 resistor in series between the power source to be measured and ground

and measuring point from the resistor interaction and ground

solve the formula for R2 : Vo = VCC*R2/(R1+R2) where R1= 10K,VCC = 20V & Vo = 4V

All the best

Bobi
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