I made a Sallen Key Filter to block oscillation from a strain gauge. Oscillation was around 20 Hz, so I made the break frequency 1.6 Hz in the filter since those are passive parts that I have on hand. It did it's job. Circuit/pic is attached.
The problem is that when I extract data to an ADC (24 bits), I get a slower oscillation of around 0.1 Hz. Well, turns out that is the RC time constant of resistor and capacitor pair. If had to guess, this is do to the feedback cap? I imagine that since the strain gauge is DC, that the feedback cap, at some point stops charging and begins to discharge (at the rate of the RC time constant) while op amp adjusts. Does that sound right?
If so, how do I fix this? For some reason, something is telling me to put a resistor in parallel to the feedback cap. Howver, I have no idea what is making me think that. Any ideas? Maybe equating R1 to R2 and C1 to C2 was a naive thing to do?
The problem is that when I extract data to an ADC (24 bits), I get a slower oscillation of around 0.1 Hz. Well, turns out that is the RC time constant of resistor and capacitor pair. If had to guess, this is do to the feedback cap? I imagine that since the strain gauge is DC, that the feedback cap, at some point stops charging and begins to discharge (at the rate of the RC time constant) while op amp adjusts. Does that sound right?
If so, how do I fix this? For some reason, something is telling me to put a resistor in parallel to the feedback cap. Howver, I have no idea what is making me think that. Any ideas? Maybe equating R1 to R2 and C1 to C2 was a naive thing to do?
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