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I am passing signals through an organic substrate & recording the response at different locations via differential probes that feed into my DAQ a Pico 24. See diagram below for set up. The sampled signals are in the order of 10s of mV.

I would like to also sample the output from the Op Amp so that I can get accurate time alignment of inputs & outputs. This is now at the limit of my electronics knowledge. Would this just be a matter of putting an appropriate resistor in the red question mark box?

enter image description here

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    \$\begingroup\$ Regarding the DAQ, what sort of port is Vo? Please link to the data for the precise device. \$\endgroup\$
    – Andy aka
    Mar 25, 2021 at 14:55
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    \$\begingroup\$ @Andyaka the PICO 24 is linked to in the OP. Vo can be configured as differential or 2 single ended inputs. \$\endgroup\$
    – DrBwts
    Mar 25, 2021 at 15:03
  • \$\begingroup\$ Please link to the document that fully describes what peripheral Vo is. \$\endgroup\$
    – Andy aka
    Mar 25, 2021 at 15:09
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    \$\begingroup\$ most probably you can just tie your daq input, depending on impedance susceptibility of your… test subject. It has a megaohm input impedance so it shouldn't load excessively the experiment \$\endgroup\$
    – Lorenzo Marcantonio
    Mar 25, 2021 at 15:10
  • \$\begingroup\$ @Andyaka I have, if you click on the underlined text a Pico 24 in the 1st paragraph it takes you to the page that gives the tech details of the device. \$\endgroup\$
    – DrBwts
    Mar 25, 2021 at 15:16

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At low frequencies all the Op Amp gain is fedback to reduce the error thus 200ish internal R/1e6 or under 1 mOhm and Pico scope is probably >=1M so any R value from 0 to <10k is ok. So near DC an Op Amp has almost ideal voltage source performance but with active current limiting.

hence my simulation boosts the current but feedback overcomes to null the Vbe drops.

You can also look at my swept f controlled current source that reads impedance or cell EIS directly from voltage . ( I doubt anyone knows how to do this in the EIS community, yet every time I think so, I am often proven wrong later)

I have no experience in your field but only as a test/design electronics expert for instrumentation.

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