Two Point Liquid Nitrogen Level Controller

The Two Point Liquid Nitrogen Level Controller, together with the appropriate probe, provides the necessary control for the automatic filling of a nitrogen container. Two platinum resistance thermometers (PT100) are used as level detectors. One sensor is located in the desired upper position, while the second sensor is placed at the appropriate lower position. At liquid nitrogen levels, the resistance of the platinum resistance thermometer (PT100) falls to around 20 ohms (at ambient temperature, the resistance is 100 ohms). When a constant current source is passed through the sensor, it can be seen that when the sensor is covered, the voltage developed across the sensor is considerably different from that of an uncovered sensor. This voltage difference is used to switch on and off a solenoid valve, which controls the flow of liquid nitrogen. If for any reason, a probe fault occurs, a fault indication is given and the valve is inhibited.


  • Two fixed levels
  • Probe fault indication
  • External level adjustment
  • High and low indication
  • Variable mains input



  • Standard Eurocard housed in KM6-11 module
  • Mains Input: Standard - 240 Volts A.C. 50Hz - Nominal - 90 - 260 Volts A.C. 50 HZ
  • Solenoid - Standard 240 Volts A.C. - Optional 24 V AC/DC or 110 V A.C.
  • Probe - Standard PT100 x 2