Hi, I am a teacher working on a lab activity involving op amps and I have basic circuit knowledge i.e. stuff from college physics books. I have a parallel plate capacitor setup and I am hanging a small steel bb from a string between the plates. This is basically the same setup as Franklin's Bell. The charge from the plates jumps onto to bb whenever the pendulum swings and makes contact with one of the plates. Once it is charged it will swing back to the other plate and discharge and pickup the opposite charge and in turn swing back to the original plate and thus the process repeats.
There is around 1kV between the plates give or take a few 100 V. I am trying to use an 741 Op Amp to amplify the current once the bb touches one of the plates. At the moment I am going for maximum gain and therefore I am using it in an open loop configuration. I have not been able to detect the bb, but I have been charging an aluminum plate through friction/inductance and touching it to the plates. A spike appears on my Pasco Capstone graph that is setup to read the voltage output from the Op Amp.
However, though I get a spike, it is sometimes inconsistent and the voltage level changes after the spike. I have a kilovolt power supply with a negative/ground/positive receptacles. Right now, my positive runs directly to the left plate. Ground is connected to my right plate and in between the ground and the right plate there is a 1 kOhm resistor to create a voltage drop. My Op Amp inputs are connected to the ends of this resistor with the idea being that when there is current there will be a small voltage that can be amplified by the op amp.
My Op Amp is powered by an Extech 18V/2A power supply. There is a blue and red receptacle. I am currently using the blue as my ground but this has me confused in that I am not sure if I should tie all of my other grounds to this one. I have a ground from my Pasco voltage sensor that consists of a red and black cable. The red one is connected to the output of the Op Amp and the black one is connected to the blue output of the Extech power supply that serves as my ground. I also have the ground from by kiloV power supply but I'm not sure if this is supposed to be connected to the other two grounds. (not even sure if the blue Extech is ground)
Strange Occurrence: When I turn on the Extech to power the Op Amp, my Vout jumps to whatever voltage I have the Extech set to, even if the Op Amp inputs aren't connected. If I change the Extech voltage, the Vout changes. I've even tied the inputs together i.e. no voltage difference on the input and still the same thing. I thought that Vout =0 if there was no voltage difference.
Final thought, how likely is it that I could pick up a signal from the bb with two Op Amps if one Op Amp doesn't do the trick?
Thanks.
There is around 1kV between the plates give or take a few 100 V. I am trying to use an 741 Op Amp to amplify the current once the bb touches one of the plates. At the moment I am going for maximum gain and therefore I am using it in an open loop configuration. I have not been able to detect the bb, but I have been charging an aluminum plate through friction/inductance and touching it to the plates. A spike appears on my Pasco Capstone graph that is setup to read the voltage output from the Op Amp.
However, though I get a spike, it is sometimes inconsistent and the voltage level changes after the spike. I have a kilovolt power supply with a negative/ground/positive receptacles. Right now, my positive runs directly to the left plate. Ground is connected to my right plate and in between the ground and the right plate there is a 1 kOhm resistor to create a voltage drop. My Op Amp inputs are connected to the ends of this resistor with the idea being that when there is current there will be a small voltage that can be amplified by the op amp.
My Op Amp is powered by an Extech 18V/2A power supply. There is a blue and red receptacle. I am currently using the blue as my ground but this has me confused in that I am not sure if I should tie all of my other grounds to this one. I have a ground from my Pasco voltage sensor that consists of a red and black cable. The red one is connected to the output of the Op Amp and the black one is connected to the blue output of the Extech power supply that serves as my ground. I also have the ground from by kiloV power supply but I'm not sure if this is supposed to be connected to the other two grounds. (not even sure if the blue Extech is ground)
Strange Occurrence: When I turn on the Extech to power the Op Amp, my Vout jumps to whatever voltage I have the Extech set to, even if the Op Amp inputs aren't connected. If I change the Extech voltage, the Vout changes. I've even tied the inputs together i.e. no voltage difference on the input and still the same thing. I thought that Vout =0 if there was no voltage difference.
Final thought, how likely is it that I could pick up a signal from the bb with two Op Amps if one Op Amp doesn't do the trick?
Thanks.
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