A liquid nitrogen level control system ensures that the LN₂ within a storage dewar or cryogenic vessel remains within a desired range. When thermistors are used as level sensors, the system leverages the temperature-dependent resistance of these components to detect the presence or absence of LN₂ at specific heights.
- Control Logic: The Low Thermistor initiates the FILL cycle when it detects the tank is Empty or the liquid nitrogen level has dropped below the low-level threshold. This triggers a LOW ALARM Timer (default: 10 minutes). If the timer expires without the level rising above the Lower Thermistor, the system activates both audible and visual alarms, as well as the REMOTE Contacts changing state, indicating a sustained low-level alarm condition.
If the LN₂ level rises during the FILL cycle, and is detected by the Low Thermistor before the timer expires, the LOW alarm condition is canceled and does not activate.
As the liquid level continues to rise until it reaches the HIGH-Level Thermistor, where the controller disables the FILL solenoid, stopping the fill process. This cycle repeats as LN₂ evaporates over time.
To prevent overfill, a HIGH-ALARM Thermistor is typically positioned approximately 1 inch above the HIGH-Level Thermistor. If liquid nitrogen inadvertently reaches this point, a HIGH-LEVEL alarm is triggered, indicating a potential overfill condition.
- Level Controller: A RISC microcontroller running proprietary firmware processes thermistor inputs and controls fill/vent valves and alarm output conditions.
- Front Panel: LED indicators for all control and alarm monitored conditions
- Push-Button: Tactile push-button switches to activate FILL / STOP or Alarm MUTE
- Thermistors: Temperature-sensitive resistors are placed at various vertical positions determine liquid level control and alarm status.
- Type-T BypassThermocouple: A Type-T thermocouple is positioned to monitor the temperature of the incoming cryogen during transfer into the storage tank. The control system continuously measures this temperature to distinguish between cold liquid nitrogen and warmer gaseous nitrogen. Based on the detected phase, the controller actuates the appropriate valve—engaging the FILL valve when cold liquid is present, or switching to the BYPASS-VENT valve when warm gas is detected, venting to atmosphere until cold liquid is detected. Bypass can be disabled if not required.
- Safety and Alarms: The system includes audible, visual and REMOTE alarm contact change for low LN₂ levels, sensor faults, or overfill (High-level) conditions.
- Solenoid Valves: 24VDC Bypass and FILL solenoid valves allow LN₂ flow based on control signals.
- Power Supply: 100-240VAC 50/60HZ input to 24VDC @ 2A output controller power.
- REMOTE ALARM CONTACTS: Contacts change states during ANY alarm condition
- 5A @ 120VAC / 4A @ 30VDC
CONTACT US FOR MORE DETAILS OR TO DISCUSS YOUR APPLICATION OR PROJECT