Abstract: Double-junction thermocouple sensors located at axially spaced measurement zones within an elongated probe are interconnected in series to produce a combined output from differential signals generated by the sensors in response to unequal heating of the junctions. Axial heat flow between measurement zones is controlled to modify the combined output in a corrective direction with respect to a linear function of liquid level between the measurement zones.

Abstract: A liquid coolant measuring instrument for a nuclear reactor vessel measures the liquid coolant level by utilizing the thermal characteristics of the medium surrounding the instrument. The instrument has an elongated cylindrical body having a number of difference thermocouples disposed within at various levels. A sectional electrical resistance heating element is located within the elongated body. The heating element heats one junction of each difference thermocouple and by monitoring the increase in temperature signal at different levels within the vessel, the liquid level can be determined. The instrument is also provided with a shield tube that surrounds the instrument forming an annular space therebetween. Liquid coolant enters the tube through a bore having a baffle that strips entering liquid of entrained non-liquid bubbles such as steam and gasses, thereby providing measurement for the actual liquid coolant level and not the expanded coolant level.