humidity sensor (prelim. report)

[Claude Petitjean <claude.petitjean@psi.ch>]

Dear Peter and Bernhard,

This is a little pre-avis:

since 2 days, CHUPS is running with the humidity sensor (PURA)
installed and in operation. Sasha will certainly send you today
a report and some questions to the manufacturer, and he is also
prepared to participate in tomorrows teleconf.

Here is, what we encoutered this morning in the experimental hall:

- the humidity readings came down below the 1 ppm level, but there
   the readings seem to be strongly dependent on the temperature of
   the sensor itself. Whatever the manufacturer means with his
   specification of operating temperature = "-20 to +40C temperature
   compensated", there is a strong temperature dependence visible.

- it seems to be necessary to keep PURA at a stable temperature
   to a fraction of a degree C. Under these circumstances, the
   calibration points are in the air, since no environment temperature
   is given on the calibration sheet.

- as a test one of the puffer volumes was heated to see whether some
   excess water vapour is detected, but nothing was observed.

- the dummy tpc volume was disconnected yesterday in order to
   eliminate it as a source of humidity and to have quicker cleaning
   cycles.

- the flow rate is 2.2 liters/s - well within the specified 1-5 l/s.

- further tests were made, e.g. with the filter device in the gas
   steam in front of PURA. Sasha et. al. will report on this.

Prelim. conclusions: without understanding the temperature dependences
of PURA it will be difficult to extract clear conclusions.

With best regards

Malte and Claude