Cryogenic Level Detection Using Pulsed RTD Heating
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Solution Overview
Problem
Existing methods for determining the position of the gas/liquid interface in cryogenic tanks, particularly for helium, face challenges such as high power consumption, slow response times, and difficulty in distinguishing between liquid and gas states across a wide temperature range, especially when using self-heated resistance temperature detectors.
Innovation Solution
A method involving a self-heated resistance temperature detector that applies a heating pulse and measures the temperature after the pulse has ended, using a threshold criterion to differentiate between liquid and gas states based on temperature differences, with parameters optimized to achieve low power consumption, rapid response, and accurate level detection across the 1.0 to 4.2 K temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a self-heated resistance temperature detector is used to detect liquid level in cryogenic tanks, then the device can operate in a wide temperature range, but the power consumption increases and the response time becomes slow
Solution Approach 1:
The patent applies periodic current pulses to the resistance temperature detector instead of continuous current. The pulse width is controlled to be a small fraction of the period, allowing the detector to be heated only during the pulse and then cool down during the off-period. This periodic action significantly reduces average power consumption while maintaining the ability to detect temperature differences between liquid and gas states across a wide temperature range.
Solution Approach 2:
The patent dynamically adjusts the operating parameters including pulse width, period, and amplitude based on the detected state. The system transitions from static continuous heating to dynamic pulsed heating, optimizing the balance between power consumption and detection capability at different temperatures and states (liquid vs gas).
2Measurement precision
If the current through the detector is increased to improve signal strength, then the temperature difference between liquid and gas states becomes more detectable, but the Leidenfrost effect occurs making it difficult to distinguish between liquid and gas states
Solution Approach 1:
The patent applies partial action by using current pulses with width being a small fraction of the period, providing just enough heating to create detectable temperature differences without excessive heating that would cause the Leidenfrost effect. This optimized partial heating maintains measurement precision while preserving reliable state distinction.
Solution Approach 2:
The system performs preliminary testing to determine optimal pulse parameters before actual measurement, ensuring the heating is sufficient for detection but not excessive enough to cause Leidenfrost effect. The pulse width and amplitude are pre-calibrated to operate in the optimal range.
3Measurement precision
If the detector is moved continuously to determine liquid level, then the measurement can be obtained, but the device requires moving parts and sliding sealing increasing complexity
Solution Approach 1:
The patent makes the detector self-service by enabling it to determine its own state (liquid or gas) through autonomous temperature measurement and comparison with reference values. The detector automatically identifies when it crosses the liquid-gas interface and generates level indication signals without external intervention, eliminating the need for continuous movement or complex sealing mechanisms.
Solution Approach 2:
The patent replaces the mechanical dip-stick approach with a thermal field-based detection method. Instead of mechanically moving the detector through the liquid column, the system uses thermal properties and electrical resistance changes to detect the liquid level, substituting mechanical movement with thermal sensing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables a low-power, high-resolution (better than 1 mm) helium level indicator with a short response time (less than 250 ms) and a robust liquid vs. gas criterion, valid across the entire temperature range, using a simple and reliable thermal device.
Implementation Method 1
the power and duration of this heating pulse being sufficient for overheating the detector at the end of this heating pulse to a temperature T heated above at least the temperature of its environment T env
Implementation Method 2
the cooling down of the initially overheated detector toward the temperature of the environment
Data Source
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AI summary
A method and apparatus to for indicating the level of a liquefied gas in a cryogenic tank having a probe and a controller are presented. The probe is a resistance temperature detector (1). The controller applies a heating pulse to the detector and performs a single resistance measurement after the heating pulse. The overheating of the sensor and the time interval for the measurement are found in a separate set of test experiment. As a result, for the temperature sensors with negative temperature coefficient, the resistance of the sensor in gas is below some unique characteristic value, which can be used like a threshold criterion to distinguish between the liquid and the gas in a wide temperature range. For the sensors with positive temperature coefficient, the resistance of the sensor in gas is bigger than some unique characteristic value, which can be used like a threshold criterion to distinguish between the liquid and the gas in a wide temperature range.