Short-Cycle Protection Device for Mechanically-Cooled Germanium Detectors

• Avoids detector degradation due to short thermal cycles
• Independent monitoring of AC power and current
• Jumper-selectable bias shutdown inputs
• Flexible setup and protection thresholds
• Programmable warm-up and cool-down timing
• Simple, automatic and robust

The Cryo-Safe answered a need for automated monitoring of the power and operation of a mechanically-cooled germanium detector in a system we were developing. Because we could not find an off-the-shelf solution, we had to solve our immediate problem with an unwieldy approach which required additional code development and a programmable controller. When the same problem arose again in the design of another system, we recognized there was a general need for an off-the-shelf solution. The Cryo-Safe was born.

A germanium detector cannot safely exceed certain warm-up thresholds without requiring a complete thermal cycle. This becomes a problem when mechanically-cooled detectors are operated in unattended environments where power outages may not always be recorded.

To provide the required monitoring and simplify assurance of complete warming cycles, the Cryo-Safe monitors and controls the AC power supplied to the Joule-Thompson cooler compressor motor, monitoring for power loss and/or time the compressor is switched off. Power loss durations are monitored and compared to a user-specified "Power Loss Threshold". Once cooling is lost beyond the threshold time, the Cryo-Safe interrupts power to allow a full thermal cycle before power is reapplied.