The liquid nitrogen levels of our cryostats are monitored with electronics designed from industrial components. The levels are measured with capacitive sensors from Cryomagnetics or other companies. The calibrations, measurements, alarms and automated refills are easily managed with a process controller (Eurotherm model 3504).

Intuitive interface

The unit measures and displays permanently the liquid nitrogen level with a bar graph and a number that are visible quite far away from the cabinet. Only one button is required to start / stop manually a refill. The message "Refilling..." is displayed when filling.

When the low level is reached, an alarm is displayed in red and a fill is automatically launched. If the fill fails after a certain amount of time, it is automatically stopped. The alarm is maintained and the level continues to be measured and displayed until the user acknowledges the alarm.

Easy settings

The level monitor is calibrated in a very few steps:

• fill the cryostat in liquid nitrogen
• enter the Settings mode
  
• raise the capacitive sensor and confirm the low level value
• lower the capacitive sensor and confirm the high level value
• quit the Settings mode

The low and high levels, the alarm level and the fill timeout can easily be modified from the Settings menus according to the user wishes.

Full remote control

Computer control via RS-485 and Ethernet is available. All parameters can be read and set, even the configuration of the sensor. The communications are based on the Modbus communications protocol which has become a de facto standard in industry. We provide a Modbus XOP and a Procedure for controlling the level monitor with Igor Pro.