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Sonsivri > Electronics > General Electronics (Moderators: o2, pickit2) > Low current measuring
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« on: April 19, 2010, 02:42:09 02:42 »
hi friends,

I need your help.
I want to measure low current, ac bipolar squarewave from 0 to 20mA, 75Hz.
What is a good method for it with precision result?
Thanks in advance.
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LabVIEWguru
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« Reply #1 on: April 19, 2010, 04:43:15 04:43 »
you could put a 250 ohm resistor across the 20 ma = 5 volt with a scope or dvm
If you want to measure it with an A/D use an op-amp to offset it "up" to all positive into an A/D
almost anything will digitize at 75 Hz
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« Reply #2 on: April 19, 2010, 05:43:49 05:43 »
Look on HCPL7800 (or analog) 10 Om shunt on input , optical isolated bipolar out .
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DreamCat
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« Reply #3 on: April 19, 2010, 09:10:29 09:10 »
which kind value you want to measure? peak current or average current value ?
these need difference method.
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« Reply #4 on: April 20, 2010, 02:00:13 02:00 »
Sorry for the delay. I have the problem with my connection. 
I want to measure only the peak value.
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« Reply #5 on: April 20, 2010, 05:11:43 05:11 »
like LabVIEWguru said , you can use a resistor convert it to voltage, and use A/D converter get the peak voltage. this need very fast.

or you can peak voltage detector got it. there is many peak voltage schematic you can search.

http://images.google.com.hk/images?q=peak%20voltage%20detect
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« Reply #6 on: April 21, 2010, 03:33:43 03:33 »
I am building some circuit for it.
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