Giacomo, Keita, Lisa


 This entry is just for reference, now we have  this problem . 

Before the WFS decided to go in a permanent and irreversible bad state we experienced a moment of happiness 
as the calibration of the DC signal path was actually making sense (the difference between what we measure on the ADCs WFS SUM channels and what we expect is within 10%).


 Direct power measurement on IOT2 

- IMC unlocked

Total power in the WFS path combined (before the first BS IO_MCR_BS2, nominally 50/50: 2.25 mW)
Power in front of WFS_A (in reflection from BS2): 0.95 mW
Power transmitted after BS2: 1.30 mW
Power in front of WFS_B = 1 mW (after the second BS IO_MCR_BS3)
Power going to the camera (transmitted by the second BS IO_MCR_BS3): 0.27 mW

Power reflected by WFS_A: 0.13 mW
Power reflected by WFS_B: 0.1 mW

- IMC locked 
  Total power in the WFS path combined: 250 uW


 Expected number of ADC counts with IMC unlocked and WFS interface in high gain mode 

WFS DC transimpedance = 1000 V/A
Diode Responsivity = 0.8 A/W
ctsPerVolts = 1638  counts/V
DC WFS interface gain = 10

==> 13104 counts/mW 

Expected 
ctsWFS_A [counts] = 13104 [counts/mW] x (0.95-0.13)mW = 10745 counts
ctsWFS_B [counts] = 13104 [counts/mW] x (1.0-0.13)mW = 11794 counts 

 Measured number of ADC counts with IMC unlocked and WFS interface in high gain mode

WFS_A_SUM = 9272;
WFS_B_SUM = 11014;

Dark offset
WFS_A_SUM = -1215;
WFS_B_SUM = 25;

Measured
ctsWFS_A_SUM = 9272 - (-1215) = 10487 counts
ctsWFS_B_SUM = 11014 - 25 = 10989 counts 

 Laser Calibrator D1201258 on WFS_B, high gain mode 

4mW @ 980 nm 

Measured ctsWFS_B_SUM = 35037;

We don't know the exact responsivity of the Q3000 diodes at 980nm, but it should be between 0.5 and 0.6 A/W.

==> This measurement gives us 0.54 A/W