Liquid-level measurement conductance method

Thermal Methods Level-measuring systems may be based on the difference in thermal characteristics oetween the fluids, such as temperature or thermal conductivity. A fixed-point level sensor based on the difference in thermal conductivity between two fluids consists of an electrically heated thermistor inserted into the vessel. The temperature of the thermistor and consequently its electrical resistance increase as the thermal conductivity of the fluid in which it is immersed decreases. Since the thermal conductivity of liquids is markedly higher than that of vapors, such a device can be used as a point level detector for liquid-vapor interface. 

If the reactor has a closed cooling system, it is recommended to use a thermal conductance type level meter composed by an electric heater and a differential thermocouple, to measure the liquid level inside of the reactor vessel. This method does not have good accuracy to determine precisely the level position, however, it is the safest way to assure that the reactor core is covered by the cooling liquid. 

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