Princeton Instruments NIRvana-LN, User Manual, Page: 37 / 122

Chapter 4 System Setup 37
4.10 Fill the Dewar
CAUTION!
!
Because of the low operating temperatures, cryogenically-cooled
detectors must always remain powered ON when Liquid Nitrogen
(LN) remains in the dewar.
If detector power is turned off with liquid nitrogen remaining in
the Dewar the array temperature will drop below the array’s
normal operating temperature of -190°C. The array will not work
properly until the power is turned back on and the array has
warmed back up to -190°C.
Always keep the detector powered ON following the completion
of all experiments until all LN has either been removed or
allowed to evaporate from the dewar, and the detector has
warmed up to ambient temperature.
WARNINGS!
1.
Always wear protective equipment when working with Liquid
Nitrogen. Even minimal contact with LN can cause severe injury to
eyes and skin. Avoid contact with the splashing that will invariably
accompany the pouring of LN into a room temperature Dewar.
2.
Always be careful when removing the Dewar filler cap if there is
LN present in the Dewar. Pressure due to nitrogen gas can cause
the cap to fly out when the retaining nut is loosened, possibly
spraying you with liquid LN, which can cause severe injury.
NIRvana-LN detectors use liquid nitrogen to reduce the temperature of the array. The liquid
nitrogen is stored in a Dewar that is enclosed in a vacuum jacket for minimal external
thermal losses. The chip temperature is regulated by a heating element driven by
closed-loop proportional control circuitry. A thermal sensing diode attached to the cooling
block of the detector monitors the array temperature. Although the array temperature can be
thermostatically controlled from 25°C to -194°C, pixel gain and offset corrections will be
optimal when the camera operates at its default temperature of -190°C.