Hello, I'm a graduate student working in geology and geophysics and (an unfortunately small) part of my thesis is to develop a seismic acquisition system to grab signals in the range of 1kHz to 20kHz.
I've built an amplifier around the LT1115 to amplify the signal from accelerometers and have run into a myriad of issues, most of which have been resolved (likely due to poor ground planes). My last major challenge is a 60Hz signal, which I'm assuming is induction from wall line from the other (commercial) amplifiers I'm using or something along those lines. What I've found is that my 1kHz to 20kHz signal rides on top of the 60Hz signal, which ordinarily wouldn't be a problem, but the inducted? 60Hz in some areas seems to be amplified to my maximum voltage of +/-10v, thus often destroying my higher frequency signal.
My questions are: does it make sense that I could be amplifying a 60Hz signal even though I believe I do not have any 60Hz signal electrically(physically?) connected to my system. The LT1115 circuit supposedly amplifies ~100 times (in reality it's more like 50) and an audio amplifier adds another 10 fold gain and by that point I'm partially blasting out of +/-10v. I've noticed when I have an oscilloscope hooked up to nothing in my lab I see a 60Hz signal in the range of 25mV. Nearly all of my wire for my amplifiers/accelerometers is shielded and twisted.
And are there better resistor capacitor pairs than others for just doing a standard high pass filter? I tried a 1uF cap and a 100ohm resistor in a high pass formation and it seems to get rid of 60 Hz noise, though I am a bit nervous about the other signal it might be killing off as the 1/2(pi)RC for the pair is 1.5kHz as well as some inconsistent phase shift it might produce if I use the same filter with components that have varying tolerances on 8 separate channels. Is there a better way to do a high pass filter where you don't have to worry about a phase shift?
Last one, it seemed like when I used my high pass filter between the accelerometers at the amplifier, I got nothing (60Hz or 10kHz). I didn't test that in depth with other amplifiers, so there could have been something else wrong, but does that make sense at all?
I've built an amplifier around the LT1115 to amplify the signal from accelerometers and have run into a myriad of issues, most of which have been resolved (likely due to poor ground planes). My last major challenge is a 60Hz signal, which I'm assuming is induction from wall line from the other (commercial) amplifiers I'm using or something along those lines. What I've found is that my 1kHz to 20kHz signal rides on top of the 60Hz signal, which ordinarily wouldn't be a problem, but the inducted? 60Hz in some areas seems to be amplified to my maximum voltage of +/-10v, thus often destroying my higher frequency signal.
My questions are: does it make sense that I could be amplifying a 60Hz signal even though I believe I do not have any 60Hz signal electrically(physically?) connected to my system. The LT1115 circuit supposedly amplifies ~100 times (in reality it's more like 50) and an audio amplifier adds another 10 fold gain and by that point I'm partially blasting out of +/-10v. I've noticed when I have an oscilloscope hooked up to nothing in my lab I see a 60Hz signal in the range of 25mV. Nearly all of my wire for my amplifiers/accelerometers is shielded and twisted.
And are there better resistor capacitor pairs than others for just doing a standard high pass filter? I tried a 1uF cap and a 100ohm resistor in a high pass formation and it seems to get rid of 60 Hz noise, though I am a bit nervous about the other signal it might be killing off as the 1/2(pi)RC for the pair is 1.5kHz as well as some inconsistent phase shift it might produce if I use the same filter with components that have varying tolerances on 8 separate channels. Is there a better way to do a high pass filter where you don't have to worry about a phase shift?
Last one, it seemed like when I used my high pass filter between the accelerometers at the amplifier, I got nothing (60Hz or 10kHz). I didn't test that in depth with other amplifiers, so there could have been something else wrong, but does that make sense at all?
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