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Wed Nov 28 21:51:52 2007, tobin, Configuration, PSL, ISS
Thu Nov 29 15:17:53 2007, rob, Configuration, PSL, ISS
Mon Dec 3 22:20:09 2007, tobin, Configuration, PSL, ISS
Wed Nov 28 21:51:52 2007
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I replaced the front-end differential receivers for the ISS's "inner-loop" sensor and monitor diode inputs with lower-noise
's (formerly THS4151's). I verified operation by taking the transfer function from the "PD+" and "PD-" inputs (separately) to the testpoint following the differential receiver; the surgery appears successful.
I measured the dark spectra at the ISS's DC PD BNC ports and found a noise floor of ~ 16 nV/rtHz, compared with a floor of ~ 22 nV/rtHz last week. This seems to add up, assuming the DC PD port has 0dB gain: the 4131 has a rated noise of 1.3 nV/rtHz and the 4151 a noise floor of 7.6 nV/rtHz, a difference of 6 nV/rtHz. The other change made in that time was to add a larger power supply bypass capacitor in the PD.
There are two of the old 4151 chips still on the ISS board on the two "outer-loop" channels that we don't use. If I dig up any more 5131's I will replace these too for completeness.
There is currently no light on the ISS diodes; I'm not sure where it's intended to come from.