Alfa refrigerator fails 18apr06
One of alfa's refrigerators (it has 2) failed
on 18apr06 around 19:00 ast (a change over from generator to commercial
power took place at 19:00).The 20K stage dewar temperature warmed up to
about 50K (by 1am 19apr06). At 11 am 19apr06 the electronics turned the
faulty fridge off. The 20K stage dewar temperature then dropped down to
20K around 12:00 19apr06. The 70 K stage has warmed up from 80K to about
To check the system temperature after the refrigerator
failed, the cal was fired on/off for 240 seconds on 19apr06 at 15:00.
The a2010 data from 18apr06 and 19apr06 was also looked at to see what
had happened to Tsys.
The plots shows alfa
tsys for 18apr06 and 19apr06 (.ps) (.pdf):
Page 1 Top: This is Tsys versus za. + are polA and * are polB (the
polb values have been offset by .1 deg za for plotting). Each pixel of
alfa is color coded. The points at za=8 deg are the data taken on 19apr06
at 15:00 with the single refrigerator. The points at za=8.5 are all of
the a2010 calon/offs taken during march06 that are close to za=8deg. You
can see that the 19apr06 values have a higher tsys.
Page1 middle: This plots Tsys versus pixel number. PolA is black
and polB is red. The + are the average values for mar06 (at za=8.5). The
* are the 19apr06 data taken at 15:00.
Page 1 bottom: This is the change in tsys 19apr06 minus the average
value for mar06 (about za=8.5). Tsys has increased by 2 to 3 degrees Kelvin.
Page 2: This is the A2010 cal values for 18apr06 and 19apr06.
This data was taken at a za of 11.5 degrees (which has a Tsys a little
higher than the 8.0 data). The top plot is polA and the bottom plot is
A2010 continued taking data on 19apr06. You can see that tsys continued
to come down till about 18:30 when it leveled off. The change in tsys after
the leveling off is only 1Deg K.
Each pixel is plotted in a different color (same code as page 1).
Dashed horizontal lines show the starting Tsys for each pixel before the
The red vertical dashed line is when the refrigerator failed.
The dashed green line shows when the 240 cal on,offs from page 1 were taken
on 19apr06 at 15:00. The tsys values are also plotted here.
One of the alfa refrigerators failed at 19:00 ast on 18apr06.
The 20 K stage rose to about 50K at 1am on 19apr06.
At 11:00 19apr06 the faulty refrigerator was turned off. The 20 K stage
then dropped to 20 K.The 70 K stage has gone from 80 K to 120 K and remained
The a2010 data taken on 18apr06 had a tsys increase of 2=3 kelvins.
At 15:00 19apr06 the Tsys was about 2-3 kelvins higher than before the
failure. The dewar temperatures had stabilized.
The system temperature continued to come down until it leveled off at 18:30
19apr06 about 1 deg K above the pre failure values. This shows that the
amplifiers continued to cool after the temperature sensors had stabilized.
<- page up