(Alexa, Daniel)

With the gain setting at 0dB for the external PD:

Transimpedance = 2kOhm

Ext PD Monitor = 1.28V

Beckhoff readback = 5.17V (there is a 4x gain between the monitor and controls output)

If the external PD is a silicon diode (responsitivty = .25A/W), this implies that we have 2.6mW on the diode. Alternatively, if we believe that we have ~1mW on the diode as referenced in alog, then the responsitivty of the diode is closer to .64A/W, which resembles that of an in-gas diode. The former is more likely.  **** Next time someone is in the PSL, can you please measure the power into the diode?

Meanwhile, I also confirmed that the gain setting on the ALS fiber distribution chassis is as expected. At the ext. PD input, I read -5.0V. Placing 100kOhm resistor at the input provides 50uA of current. Thus, one expects to read V=(50uA)(2kOhm) = 100mW at the ext PD monitor, which I verified. This is consistent with the test report for this chassis, which confirmed 3.13V at 30dB with 50uA. The factor for 30dB gives a factor of 31.26 in V.

Conclusion: ALS fiber distribution is okay. Diode is different than expected or we have more power ...