| 摘要 |
PROBLEM TO BE SOLVED: To detect the liquid level accurately at high speed without causing thermal runaway in a wide temperature range with a detector of the liquid level and a temperature around the thermistor periphery. SOLUTION: This detector which takes out the difference of thermal diffusivity in gas and in liquid by self-heating of a thermistor TH connected to a power source 1 and detects the liquid level and the thermistor peripheral temperature comprises a temperature detection circuit 2 connected between the power source 1 and the thermistor TH through a resistance for temperature detection, detecting the thermistor peripheral temperature, a constant current switch circuit 3 connected between the power source 1 and the thermistor TH, changing the reference current of the thermistor driven by a constant current in order to change the property of the output voltage difference of the thermistor TH in air and in liquid over the temperature, and a controller C which can switch the temperature detection circuit 2 and the constant current switch circuit 3 and controls the constant current switch circuit 3 to make the output voltage difference larger based on the detection output of the temperature detection circuit 2. COPYRIGHT: (C)2009,JPO&INPIT
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