I have a small DC motor that is being used to rotate a centrifugal pump. The motor can supply a variable voltage from 0-30V (controlled on the power supply). I also have a function generator hooked up to the motor, so that I can create a pulsatile waveform from the pump output. In order to operate the motor with the function generator, I had to create an emitter follower, used as a current amplifier (see picture). What I'm trying to do is calculate the power usage of the motor when it is running in both continuous and pulsatile modes. I have a dual-probe BNC cable connected to the motor, and have it going to an A/D board to output my data on my computer. So, essentially, I am measuring the input voltage to the motor, but I also need the input currrent, in order to calculate the power (P=V*I).
So, my question is, how do I find the current?! I was thinking that if I knew the resistance of the circuit, I could just calculate it by I=V/R, but I'm not sure if I'm finding the resistance correctly. I hooked up a digital multimeter to the two motor inputs, and measured the resistance there while zero volts were applied. I was thinking that the resistance won't change no matter how much voltage is applied to the motor, but I'm starting to re-think that because of the emitter follower circuit...though, I really don't know much about circuits, and so I'm not sure if that even matters. When I apply enough voltage to the motor to get it to start spinning, the resistance on the multimeter maxes out...I still don't understand that either. I would really appreciate any help possible! Thanks a lot!!!
So, my question is, how do I find the current?! I was thinking that if I knew the resistance of the circuit, I could just calculate it by I=V/R, but I'm not sure if I'm finding the resistance correctly. I hooked up a digital multimeter to the two motor inputs, and measured the resistance there while zero volts were applied. I was thinking that the resistance won't change no matter how much voltage is applied to the motor, but I'm starting to re-think that because of the emitter follower circuit...though, I really don't know much about circuits, and so I'm not sure if that even matters. When I apply enough voltage to the motor to get it to start spinning, the resistance on the multimeter maxes out...I still don't understand that either. I would really appreciate any help possible! Thanks a lot!!!
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