The KGW-ISOTHERM LN2 Level Controller provides automatic liquid nitrogen level regulation in open Dewar flasks for cryogenic applications including cold traps, sensor calibration, shrink-fitting, and biological sample preservation. It uses PT100 resistance temperature detectors as level probes to detect the LN2 liquid/gas interface — where the probe is submerged in liquid nitrogen at -196 °C, its resistance drops sharply compared to the gaseous phase above the liquid surface.

How does the dual-probe differential control work?

Two PT100 probes are positioned in the Dewar: the MIN probe at the desired minimum fill level and the MAX probe at the desired maximum. When the LN2 level falls below the MIN probe, the probe warms, its resistance rises, and the controller opens the solenoid valve on the LN2 supply Dewar. Liquid nitrogen flows until the level reaches the MAX probe, at which point the valve closes. In mono-mode operation, the MAX probe is placed below the MIN probe position and the controller regulates around the MAX probe with time-delayed switching — useful when a narrower level band is acceptable.

What safety features protect cryogenic operations?

The controller continuously monitors probe continuity: if a sensor cable breaks or a connector disconnects, the unit triggers an audible whistle alarm and a red blinking LED while closing the solenoid valve. The solenoid valve itself is normally closed and spring-return (fail-safe), ensuring the LN2 supply shuts off on power loss. A front-panel manual fill switch allows operator-initiated refilling without reprogramming. The recommended supply Dewar pressure is limited to 0.5 bar, and the IP 40 enclosure is rated for laboratory environments at +10 to +30 °C with up to 80% relative humidity.