I´m trying to rebuild a circuit whose schematic I have. I am using a different instrumentation amplifier but the same sensor. Using an oscilloscope at the output and putting the (vibration) sensor on a calibration exciter that produces a clean and constant vibration, the output for the first circuit is a clean sinusoidal signal, while on my new circuit it looks rather messy. As I do not have much experience with building electric circuits so far, my question is regarding the capacitors and the input resistors. I suppose that they are the reason for the different signals, as they are pretty much the only difference between the two circuits. Do I need more capacitance and also an RC-filter?

Below are three pictures: Old circuit, new circuit and both signals next to each other.

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  • 6
    \$\begingroup\$ Both LT1920 and AD625 are fine in-amps, and both should perform equivalently, but do you have them set to the same gain? Is the oscilloscope set to the same range? Those steps look like o'scope quantisation. If you're using the scope on the same range, but your second circuit is set to a lower gain, that's exactly what I'd expect to see. \$\endgroup\$
    – Neil_UK
    Nov 28, 2022 at 12:13
  • \$\begingroup\$ Yes, both circuits are set to the gain 5. On my circuit, i had to set the voltage range to +- 5V as i am adding a dc offset of around 1.6 V to the LT1920´s output for ad conversion purposes, so that might be the case. Didn´t think of that, thank you! \$\endgroup\$
    – Jan
    Nov 28, 2022 at 12:26
  • \$\begingroup\$ What is the vibration frequency? \$\endgroup\$ Nov 28, 2022 at 15:19
  • \$\begingroup\$ Can you include the values on the gain resistor for the AD625? \$\endgroup\$ Nov 28, 2022 at 15:29
  • \$\begingroup\$ The Vibration frequency is 159.2 Hz and the gain resistor for the AD625 is 20 kOhm \$\endgroup\$
    – Jan
    Nov 29, 2022 at 19:22


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