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 120 K.

    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 polB.
• 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 refrigerator  failed.
• 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.
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.

Summary:

• 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 there.
• 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.