The ORTEC Model 729A Liquid Nitrogen Level Monitor is a single-width module (NIM-standard) designed to serve as an accessory on HPGe coaxial (GEM and GMX), LEPS, Si(Li), and old Ge(Li) detectors in the field.
There are two uses for the 729A: (1) for customers whose applications will not tolerate detector warmup, (e.g., unacceptable loss of experimental data); (2) guarding against thermal cycling older HPGe detectors.
When used with the appropriate probe, the monitor will sound an alarm long before the detector can warm up as a result of loss of liquid nitrogen in the dewar. The level of liquid nitrogen is sensed by a thermistor probe in the dewar. When the liquid nitrogen falls below a safe level (approximately 1/4 of the dewar capacity), an alarm sounds and a red light on the front panel of the control module flashes a warning.
The module is totally fail-safe with a battery backup in case of power failure and an audible, flashing alarm that sounds if: (1) bin power is shut off, (2) the sensor is broken, (3) the sensor is disconnected, or (4) an attempt is made to remove the module from the bin.
Impedance considerations do not permit using the detector’s internal, high-voltage shutdown and the Model 729A together. A 3.66 m (12 ft) BNC coaxial cable for connecting the probe to the Model 729A is included.