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Voltage follower for the INA125? Answered

I need to use a voltage follower that runs off a 9 v battery (actually, two batteries so +- 9V is available), from the output of a Burr-Brown INA125 amplifier to the analog input of a DATAQ data acquisition unit. The DATAQ is running at about 1000 data points per second.  Is there a particular op-amp that would be useful in such an application?  Or would something besides an op amp be more useful?  Thanks!

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steveastrouk (author)2010-12-10

Why do you need the follower ? The output impedance of a follower is as close to zero as makes no odds, and the output of the INA 125 should be likewise, so what's the follower for ?

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Prfesser (author)steveastrouk2010-12-10

...output of the INA125 should be...

As it turns out, "should be" does not mean "is". Therein lies the problem.

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steveastrouk (author)Prfesser2010-12-10

What circuit are you using around the 125 ? What's the error you're seeing in the rest of the system ? Channel cross talk or what ? I'm leery of adding noise from another amp, if its not necessary.

If, for whatever reason (like what load does your DAQ present???), you have to add a buffer, you may as well use a INA 105 as a unity gain buffer. You can't go wrong with Burr-Brown, but whatever, you are injecting uncertainty, if not noise.

Steve

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Prfesser (author)steveastrouk2010-12-11

The circuit is pretty much lifted from the INA125 data sheet.  The input is a load cell from Aerocon:
    http://aeroconsystems.com/cart/products/20_50_100_kG_Load_Cell-20-64.htm

Used two 9v batteries in series to get +-9v.

The output of the INA125 goes to a DATAQ DI-158U (USB to computer).  Although I'm using the 5v reference of the INA125, the maximum signal at the DATAQ is about +-2.8 volts.  My thought is that I should get something close to +-5 V.

Of course I may be fulla sh*t, it wouldn't be the first time. :-)

Thanks!

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steveastrouk (author)Prfesser2010-12-11

What gain setting resistor did you use ?

S

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