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kyle.ryan@LIGO.ORG - posted 14:29, Wednesday 10 September 2014 - last comment - 16:15, Wednesday 10 September 2014(13864)

Swapped PT170B and PT180B sensor electronics

Following the recent replacement (generic maintenance) of PT120B, PT170B and PT180B Cold Cathode gauge sensor+electronics, there has been an apparent 25% discrepancy between the indicated pressures of the new PT170B and PT180B gauges -> Swapping the removable electronics between the two units has (surprisingly) resulted in both read backs being as expected in both absolute and relative pressure values

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kyle.ryan@LIGO.ORG - 16:15, Wednesday 10 September 2014 (13867)

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This result might make sense considering that these three gauges were all replaced at the same time and the electronics units were removed from the sensors to ease the installation of the sensors.  No attempt was made to keep a given electronics unit together with its associated, as received from the factory, sensor head.  These (sensor+electronics) pairs are probably factory calibrated as a set and we probably had mixed up these pairs on initial installation of the electronics units.  These units don't have a provision for user calibration.