Looking at the measurement made during the last maitenance we realised that when the PCal permanent lines were on, the noise level of the photodiodes was increasing compare to when the lines were off (see plot 1 were the reference plot is without permanent lines compare to with permanent lines with standard amplitude)
We did some more test to see were this is coming from on WE during maintenance today.
1/ Testing line injection with CALNoise
2/ Testing lines injection with PCal_Fast
1/ Testing line injection with CALNoise
First we acted on WE PCal lines using CALNoise, we switched the lines off and then tried to switch back on one line at a time to see which one were causing the noise to rise.
WE PCal has 3 permanent lines at the following frequencies and amplitude :
- 36.28 at 1.5e-3
- 38.5 at 2.0e-3
- 994.5 at 200.0e-3
The amplitudes were choosen in order to get the same SNR on all injected lines.
When putting one line at a time it appeared that the issue was coming from the 994.5 Hz line only (see plot 2 with reference plot without lines compare to when we inject only the 994Hz line).
We wanted to see the threshold in amplitude were the noise starts to increase. To test this we changed the amplitude of the 994.5Hz line starting at 2.0e-3 up to 37e-3 were we started to see the noise increase.
See plot 3 where we compare the noise without injection to the one where the 994Hz line is injected at 37e-3 amplitude.
Something intersting to note is that the noise level of Tx_PD1 and Tx_PD2 is higher for the 37e-3 amplitude than it was when injecting at 200e-3 and also when injecting all the lines at normal amplitude. It is not clear why.
We did the same test for the 38.5 Hz line to see if we would see the same effect by increasing the amplitude and the same thing append around ~30e-3.
See plot 4 comparing without lines to injecting the 38.5 Hz line at 37e-3.
Timestamps (For 60 s each time)
- Cutting line off --> 8h15'15''
- 38.5Hz (2.0e-3) --> 8h22'30''
- 36.7Hz (1.5e-3) and 38.5Hz (2.0e-3) -->8h25'30''
- 994.5Hz (200e-3) --> 8h28'00''
- 994.5Hz (2.0e-3) --> 8h32'30''
- 994.5Hz (20e-3) --> 8h34'45''
- 994.5Hz (40e-3) --> 8h38'00''
- 994.5Hz (30e-3) --> 8h40'00''
- 994.5Hz (35e-3) --> 8h41'40''
- 994.5Hz (36e-3) --> 8h43'00''
- 994.5Hz (37e-3) --> 8h44'40''
- 38.5Hz (37e-3) --> 8h46'15''
- 38.5Hz (10e-3) --> 8h47'45''
- 38.5Hz (20e-3) --> 8h50'15''
- 38.5Hz (30e-3) --> 8h53'00''
- 38.5Hz (31e-3) --> 8h55'45''
2/ Testing lines injection with PCal_Fast
One of the hypothesis on this is that it could be caused by communication issue with CALNoise. To test this we tried injecting the same lines but using the PCal _fast process directly.
Fisrt we tried to inject the 38.5Hz line at 2.0e-3 amplitude to check that it was working but accidentelly injected a noise at 10e-3. After this we were able to do the other injections but we noticed that the noise level of Tx_PD1, in particular, was higher without the calibration lines than it was before (see plot 5 where we compare the noise without noise injection that was acquired at 8h15'15'' at the beginning of this test, to the noise acquired at 9h32').
Then we tried to see if we could reproduce the same noise increase seen in the previous test with CalNoise. First we tried with the 38.5Hz line and found that the amplitude needed to get the noise increase was more around 50e-3 rather than the 37e-3 seen in the previous test (see plot 6 for the injection of 38.5Hz line at 50e-3). We did the same thing with the 994.5Hz line and found that the noise increase was seen around an amplitude of 30e-3 (see plot 7).
We also did another inejction at low frequency at 4.5Hz at 30e-3 of amplitude to see how it affected the noise level. In plot 8 we can see that it increase the noise in the same way than with the 38.5 and 994.5Hz lines.
To conclude it does not appear that this increase in noise is coming from using CAlNoise as using directly PCal_fast is not improving the noise level.
Timestamps (For 60 s each time)
- accidentely injected a 1e-3 noise --> 9h08'13''
- Cutting lines off --> 9h09'15''
- 38.5Hz (2.0e-3) --> 9h31'00''
- Cutting lines off --> 9h32'00''
- 38.5Hz (2.0e-3) --> 9h33'40''
- 38.5Hz (37e-3) --> 9h34'50''
- 38.5Hz (50e-3) --> 9h36'05''
- Cutting lines off --> 9h37'20''
- 994.5H z (200e-3) --> 9h38'30''
- 994.5H z (30e-3) --> 9h40'15''
- 994.5H z (20e-3) --> 9h41'30''
- 994.5H z (30e-3) --> 9h43'10''
- cutting lines off --> 9h44'20''
- 4.5Hz (30e-3) --> 9h45'00''
- 4.5Hz (20e-3) --> 9h46'10''
- Cutting lines off --> 9h48'00''
- Putting normal lines back on --> 9h48'50''