ll. The original Tolman-Stewart used this rotating coil and braking; they re-did their experiment about a decade later with a constantly rotating sys tem and then everything moved to ac and was easier. The recent papers from the 80s used the ac system. The problem is, the physics is harder, and we want this to be for undergrads. So we like the braking experiment better.
onitors and running at night. Ideally, we?d like to be able to run this as part of our undergraduate advanced lab, so making it an extremely low-noise environment is not ideal. But we can try. We?ve actuall y tried mu-metal, and it is not great at keeping out the magnetic fields. We?re currently considering just adding a 60 Hz notch filter.
t now the noise swamps the TIA, and brings it to the rails.
d a volt or so. We?re working with low-noise op-amps, and so they are not trimmable. We were using the LT1792 and that one we could trim and that worked well. We can and have tested the circuit with an actual hones t-to-goodness current source, and with two coils, where we send a pulse int o one coil and pick it up in the second coil. The first experiment works w ell, the second is inconclusive so far.
rotary feedthrough that one of my students found on the web:
Mercury? Gallium if you heat it a little, I wonder if there is a temperatur e spec.?
Oh dear, don't throw another monkey wrench at it. Maybe the thermal times are long enough so that he can look at differences between the two spin directions.
And no one's mentioned 1/f noise. :^)
George H.
ed to integrate the current pulse. Our thought was that integrating would allow us to integrate over the noise and be left with only the slower 0.5 s pulse. But in order to get a large current, the input impedance of the me asurement system has to be small. This is why the TIA, with its virtual gr ound at the negative input is nice, acts as zero input impedance for the cu rrent pulse. What would be the input impedance of your transistor circuit be?
ribed, but without the switch. So to prevent pinning the op-amp we added a feedback resistor also. The system we had was very unstable, even for sho rt periods of time. But we did not try it with a switch to keep the capaci tor for charging. You are right that the math is easy if we can integrate the current to get the charge. Then we only need to know the starting spee d and the total charge.
Can those be built to reject the 60 Hz noise?