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Sonsivri > Electronics > General Electronics (Moderators: o2, pickit2) > Measuring parts of a voltage
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max
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« on: July 04, 2010, 11:28:41 11:28 »
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, 11:43:14 11:43 »
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, 11:46:56 11:46 »
I have never had to do this, I think your answer is in opamps to subtract voltage.. something like this... 

http://homepages.which.net/~paul.hills/Circuits/Adder/Adder.html 
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« Reply #3 on: July 10, 2010, 02:01:23 14:01 »
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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« Reply #4 on: July 10, 2010, 06:20:50 18:20 »
As I understand the problem is measuring 10-14V as 0-4V against the ground. Proposed circuit is bellow and only simulated but not tested in reality.
V1 max current is less than 30mA.
X1 subtracts 10V from input and X2 limits the output voltage on OP to 4V.
« Last Edit: July 10, 2010, 06:37:58 18:37 by borberk » Logged
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