(see also alog 26902)
I measured the PUM coild driver noise of the ITMs at the coil driver output.
Bottom line:
- All 8 chammels (4 ITMX & 4 ITMY) show the same nosie.
- There is significant pickup in the cable running from driver to coil. This corresponsds to the 10msec bursts every 100msec mentioned in alog 26902)
- This pick-up leads to 10Hz and harmonics.
- There is some residual pickup of the same signal in the coil driver, but significantly less.
- above 10kHz there is a huge amount of junk flying around (10uV/rtHz and more !)
The 4 traces in the plots correspond to
Blue: Coil driver output, terminated with 50Ohm.
Red: Coil driver output, with cable and coil attached.
Yellow: Only cable and coil attached. Coil driver disconneced.
Purple: Measurement noise. (Only terminted breakout box)
Attached are
plot 1: 0-200Hz (for example ITMY coil 3)
plot 2 & 3: 0-100kHz (for example ITMY coil 1 & 4) Note the 3kHz line - it corresponds to a 100cts 3kH length drive, resuling in about +-2ct at the ADCs.
Stefan - can you add:
- what state the coil drivers were in for these measurements?
- state of the CD inputs: terminated; connected to AI; connected to DAC/AI; ... ?
Peter:
- The L2 cois drivers were both is state 3: Acq Off, LP On, which is the run mode. They are never switched for the ITMs. (Binary IO medm screens attached).
- The coil driver inputs were left connected to the DAC/AI. I also sent a 100ctpk, 3kHz signal into H1:SUS-ITM[XY]_L2_DRIVEALIGN_L2L_EXC, corresponing to a 2.6ctpk signal on the DAC. I did this to make sure the DAC is as least flipping bits, which raises its noise level. You can also see that signal in the plots at 3kHz. Note though that at 15Hz the total coil driver electronics + DAC noise is still less than what we pick in the cable - blue is below yellow in plot 1.
Superseded. See alog 26948