Evan G., Darkhan T.

Summary:
Foton filter coefficients have been updated for Y-end calibrated Pcal TX and RX outputs and X-end calibrated Pcal TX output. X-end RX output is unchanged because it is still affected by a clipping issue. Until the clipping is fixed, the X-end RX PD channel currently has an incorrect calibration. Our plan is to fix this before O2.

Details:
Several end station Pcal calibrations have been made since the last update for the N/V foton coefficients. The general formula for this coefficient is: N/V = 1/[ TX/WS x WS/GS x GS ] x 2 x cos(theta)/c

We compute below the new coefficients.

Y-end:
From the trend of calibrations (T1500131-v4) made since Aug 2015 to May 2016, the mean value of the ratios for TX and RX to WS accounting for optical efficiency losses is:
  TX/WS = -2.7619 V/V
  RX/WS = -3.9891 V/V

X-end:
From the trend of calibrations (T1500129-v7) made since Aug 2015 to May 2016, the mean value of the ratios for TX to WS (not corrected for optical efficiency losses) is:
   TX/WS = -3.154688 V/V
Using the only reliable optical efficiency we have, D20150804 in T1500129-v7:
   e = 0.982588
Computing the TX/WS ratio accounting for the optical efficiency is:
   TX/WS = 2/(1+0.982588) * -3.154688 = -3.1824 V/V

Working Standard:
Using the trend of working standard calibrations (T1500054-v41), the WS to GS ratio is:
   WS1/GS = 0.926745 V/V

Gold standard:
Using the two calibrations from NIST on Aug 12, 2014, and Dec, 17, 2015 (T1500036), the mean value of the GS responsivity is:
   GS = -1.7000 V/W

Power-to-force:
The power to force coefficient is 2*cos(theta)/c, where theta is the angle of incidence and c is the speed of light. From L1600019-v1, the mean of cos(theta) is 0.9884

Final results:
   Y-end TX = 1.515e-9 N/V
   Y-end RX = 1.049e-9 N/V
   X-end TX = 1.315e-9 N/V

These new values have been loaded into Foton and updated the EPICS records