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Author Topic: Protues and INA122  (Read 2353 times)
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odsk
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« on: December 10, 2010, 04:22:03 04:22 »

Hi,
Anyone tried to simulate with INA122? I am having trouble doing that.
What I want to achieve is to simulate the INA with a differential output from a sensor (wheatstone bridge).
I have Rg=1K with power supply of 10V for the INA.

Regards,
ODSK
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pickit2
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« Reply #1 on: December 10, 2010, 07:54:04 19:54 »

hint:
the INA122 has a data sheet
it has a model in Proteus
so where is your testMe.dns posted ?
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odsk
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« Reply #2 on: December 11, 2010, 05:48:37 05:48 »

OK,
Made this test circuit but there is always some offset. example the input is 0.05mv but output 0.38V instead of being 0.01. Is that normal? (Gain is 205 (RG=1K), and ref is tied to ground).
I am trying to be as precise as possible. I am trying to use it with 24PCBFA6 pressure sensor for water level indication.


Thanks,
ODSK
« Last Edit: December 11, 2010, 06:00:21 06:00 by odsk » Logged
Sideshow Bob
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« Reply #3 on: December 11, 2010, 11:59:11 11:59 »

OK,
Made this test circuit but there is always some offset. example the input is 0.05mv but output 0.38V instead of being 0.01. Is that normal? (Gain is 205 (RG=1K), and ref is tied to ground).
Set RV1 to 100 ohm. Your circuit works fine, but with RV1=1K your amplifier saturate quite easy.
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zuisti
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« Reply #4 on: December 11, 2010, 01:11:02 13:11 »

... there is always some offset. example the input is 0.05mv but output 0.38V instead of being 0.01. Is that normal? (Gain is 205 (RG=1K), and ref is tied to ground).

Hi;
You are right, this Proteus model seems has an offset error.
With shortened  input pins (Uin=0) and w/o (opened) R1 (G=5) the
output is 302 mV instead of the expected max. 1.25 mV (250 uV x 5).

Try out the offset compensation via the ref pin (datasheet, fig. 2)
or ... do not use it in Proteus (sorry :-). There are a lot of good OPAs ...
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odsk
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« Reply #5 on: December 12, 2010, 02:31:27 02:31 »

Set RV1 to 100 ohm. Your circuit works fine, but with RV1=1K your amplifier saturate quite easy.
Yes I was setting the diffrence of portential only to 114ma max (this is the output of the pressure transducer).
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