The emails below discuss the sudden cooling ~ 1 degC observed when the cryostats are filled in GRACE.

From andy@ing.iac.es Mon Jul 21 16:58:09 2003
Date: Wed, 16 Jul 2003 15:56:54 +0100
From: Andy Hide 
To: naomiteam@ing.iac.es
Subject: Temperature measurements recorded in front of DM during cryostat fill

Dear all - a brief summary of my / Peter findings this
morning as we investigated the nature of the apparent 'shock cooling' of
the DM during cryostat cooling:
 
1.  There was no temperature change with characteristic time (10s of
seconds) which would be expected if cooling was due to a 'cold air front'
being violently channelled from either OASIS or INGRID cryostats.
 
2.  There was, during the period that the door to GRACE was open, a
gradual (over 6 minutes) fall in the recorded temperature from 17deg to
15deg.
 
3.   It is not possible, based on the conditions of the test, to
determine whether this temperature drop was caused by either the cooler
ambient air in the gantry entering GRACE or the 'ambient' (large scale)
cooling caused by nitrogen dispense (ie the dispense was carried out
throughout the door-open period)
 
4.  Further test is required - meanwhile it is suggested that TOs are
given as much flexibility as possible to deconflict filling from
'sensitive periods' and that TO's (while observing H&S procedures) do not
either leave the door open longer than necessary or spill excess
nitrogen.
 
Regards
 
AH

Andy Hide
Head Telescope and Instrument Group
Isaac Newton Group

SLO 922 425 443
MOB 616974511

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From crb@ing.iac.es Mon Jul 21 16:57:42 2003
Date: Fri, 18 Jul 2003 02:43:28 +0100 (BST)
From: Chris Benn 
To: Andy Hide 
Cc: naomiteam@ing.iac.es, Kevin Dee 
Subject: Re: Temperature measurements recorded in front of DM during cryostat
    fill

More on temperature spikes.  The record below is from the thermometer
Kevin installed near the DM, during the fill evening of Jul 16.
Air in dome was warmer than in GRACE.

Initial temperature T = 16.5 deg C.

During the 2 mins after opening the double doors, the temperature
remained at 16.5.  Then:

19:54 filling started
19:55 T = 15.5
19:57 T = 15.1
20:03 T = 15.9
20:07 filling stopped, T = 15.9

i.e. on this occasion, the temperature dropped suddenly on starting to
fill INGRID.

Chris

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Last Updated: 2002 Aug 28 Chris Benn crb@ing.iac.es