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May 14, 2013 at 7:07 comment added Andy aka @scalpas if your lock-in amp is really good i.e. has very good impedance balance to ground across a wide range of frequencies, I suspect you could get decent results without an In-amp. This is definitely worth a try. Regarding the filter, yes if you have a broad range of frequencies that you test at, filtering becomes difficult in that you have to vary the cut-off frequency - not impossible, but for that reason alone it may not be worth considering.
May 13, 2013 at 22:08 comment added scalpas Thanks for the answer. - instr amp : In the text I cited they use AD624 in-amps. Do they qualify as really really good ? ;) Even if I don't completely remove the harmonic noise, reducing it would be an improvement. - wheatstone bridge. In my case, would I be balancing the bridge at the fundamental, and just measuring the 3rd harmonic at the ouput of the bridge ? If so, could I just do without the in-amp ? - filter : it's a good idea. However, the measurements are repeated at several different frequencies, over at least 2 decades, so that would imply a variable cut-off frequency.
May 13, 2013 at 20:46 history answered Andy aka CC BY-SA 3.0