Rich, Hugh, Fabrice:
Continuing the investigation to solve HAM3 noise issues. Last tests on Fridays doing the sensor correction to HEPI instead of ISI show that the noise line is still visible in the CPS, but not in the GS13. Rich suggested it might mean that the noise is introduced in the sensor correction channels (still disturbing Stage 0, but rejected by Stage 1 isolation). So we have looked at the coherence bewteen the FIR channels:
H1:ISI-HAM2_SENSCOR_GND_STS_X_FIR_IN1_DQ,
H1:ISI-HAM3_SENSCOR_GND_STS_X_FIR_IN1_DQ,
...
H1:ISI-HAM6_SENSCOR_GND_STS_X_FIR_IN1_DQ
for the X, Y and Z directions.
The coherence from HAM2 to the other channels is shown in the plot attached. It is pretty bad in the Y direction, but we don't see the coherence droping at 0.6 Hz. Next step is to look at the output of the sensor correction filters (not sure whether they are in the DAQs, I might need someone on site to look at it)
A separate comment: Hugh and I just checked which ground instruments are used where. It looks like HAM2 uses intrument A, and HAM3 uses instrument B. We probably want those two chambers to use the same sensors. We might want to investigate a bit more on HAM 3 (and fix it!) before we swap.
Here are coherences at the OUT of the Match filter. Results look somewhat similar but with cetain differences to the plots Fabrice put in. In particular, the X & Z coherences don't go as low in frequency. The Y dof does look very similar.
