Vacuum & Cooling

As concluded in the previous report we have now a reasonably well behaving cryostat since March 2008, giving better vacuum and holding time than ever before. NOTCam has remained cold since May 9th 2009 with no incidents, and we hope to beat the record of 360 days continuously cold this spring.

The alert system was improved after the accidental warm-up in April 2009 with a cronjob that will check that there are new readings twice per day, and if not, an alarm will be sent by email to staff. In November slight problems were reported with the readings (4 temperatures plus pressure) that go into the log used for monitoring and alerts. These readings are stored with a time resolution of once per minute when NOTCam is stored, and once per 10 minutes when NOTCam is used observing (this in order to avoid any extra overheads on the system). The logs were investigated, and it appeared that occasionally, and apparently only during storage, a reading could be corrupted or give just zero values, although quite seldom and irregularly with a frequency of about 1/700 measurements. It is believed that the internet plug during storage position could have a bad connection, and this is being looked at. Also, the problem only lasted until the next mounting of NOTCam, so it depends apparently on how well the plug is inserted.

The tubes of the PTR cooling system was believed to have a small Helium leak somewhere, since the PTR has to be refilled with high-quality Helium about once a month. However, it was discovered that the expansion secondary circuit tank was empty, and had to be refilled with glycol.