Sensitivity of level detection of cryogen in a storage container depends upon the temperature difference above and below the liquid surface. In order to increase this sensitivity for detecting liquid nitrogen a thin film Pt-100 temperature sensor is mounted on a commercial 1/4 watt resistance which acts as a small heater. Heater current is so adjusted that as soon as the sensor comes out of the liquid (nitrogen) its temperature rises by about 10 K within 2 seconds. Associated change in the electrical resistance is also very high and can be easily detected by very simple electronic comparator circuits. Level detection sensitivity of about 5-10 mm is obtained with this detector. Commercially available PT-100 sensor elements are quite reliable and are available at low cost. This report describes the detail characteristics and the operation of the detector.
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