Because the mechanical chopper on absorption measurement bench was broken,
we bought new one (Stanford research instruments SR540).
Today I repalce the controller (motor driver with local oscillator) of the chopper.
Old chopping motor and wheel are unchanged, since we want to keep the setup
as much as possible.
After the replacement, I checked all of cable connections.
And then, I found that many cables are unplugged.
Tomorrow I will check the absorption measurement system by using reference samples.
On friday afternoon Flaminio and me noticed that the chopper frequency is quite unstable, about 5Hz of standard deviation. The old one was not that unstable. We should check it.
Two days later, I found that the wheel was stopped.
Therefore, I and Manuel replace the new motor with chopper also.