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shunt measure

 
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dolphin



Joined: 23 Feb 2005
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shunt measure
PostPosted: Mon Sep 05, 2005 2:01 pm     Reply with quote
at first for measure the current i use shunt resistive wire and when i measure voltage i see 65mVac (with voltmeter) how can i amplifier this voltage AND how can i convert to line voltage(in turkey is line voltage 220V)
DO YOU KNOW ANY CIRCUIT TO MEASURE AND CONVERT FOR MICRO
THAK YOU EVERYBODY....
SherpaDoug



Joined: 07 Sep 2003
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Location: Cape Cod Mass USA

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PostPosted: Mon Sep 05, 2005 2:23 pm     Reply with quote
A first very big question is wether the ground pin of the PIC is connected to one end of the shunt. If it is connected then a simple opamp amplifier will do the job, BUT that means all your PIC circuitry is connected to potentially deadly line voltage.

Usually the PIC DC circuits are isolated from the AC line volatge. You can use a "shunt transformer" or an "isolation amplifier"

Tell us more about your circuit and we can help you better.
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Eugeneo



Joined: 30 Aug 2005
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PostPosted: Mon Sep 05, 2005 2:54 pm     Reply with quote
This was very helpful.

Linear optical iosolation

http://www.ccsinfo.com/forum/viewtopic.php?t=24246&highlight=isolation
Guest
PostPosted: Mon Sep 05, 2005 3:46 pm     Reply with quote
in this circuit
is it need amplifier this output voltage to 5 volt??
for micro???
beacuse i read 65mv when 5A is cross the shunt.
Sherpa Doug
Guest
PostPosted: Mon Sep 05, 2005 7:12 pm     Reply with quote
Anonymous wrote:
in this circuit
is it need amplifier this output voltage to 5 volt??
for micro???
beacuse i read 65mv when 5A is cross the shunt.


It depends on what you are doing. If you have an 8 bit 5V A/D then each LSB is 5V/256=19mV so 5A gives you 3 counts. That is pretty bad for an A/D but might be enough to tell if a 5A load is ON or OFF. If you have a 12 bit converter the same 5A gives 53 counts. You can now measure your 5A load to 2% accuracy! That is enough for lots of applications.

SherpaDoug
Sherpa Doug
Guest
PostPosted: Mon Sep 05, 2005 7:15 pm     Reply with quote
Anonymous wrote:
in this circuit
is it need amplifier this output voltage to 5 volt??
for micro???
beacuse i read 65mv when 5A is cross the shunt.


It depends on what you are doing. If you have an 8 bit 5V A/D then each LSB is 5V/256=19mV so 5A gives you 3 counts. That is pretty bad for an A/D but might be enough to tell if a 5A load is ON or OFF. If you have a 12 bit converter the same 5A gives 53 counts. You can now measure your 5A load to 2% accuracy! That is enough for lots of applications.

SherpaDoug
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