초록 ▼

Differential outputs produced by twin thermoresistive sensors are used to determine the level and flow of a medium. Separate constant current sources supply power to each sensor so that one constant current source supplies sufficient current to cause significant self-heating of the sensor (hot senso

Differential outputs produced by twin thermoresistive sensors are used to determine the level and flow of a medium. Separate constant current sources supply power to each sensor so that one constant current source supplies sufficient current to cause significant self-heating of the sensor (hot sensor) and the other constant current source supplies relatively little current with insignificant self-heating of its corresponding sensor (cold sensor). Resistive changes in the sensors produced by level and flow changes of the medium produce measurable voltage changes, thereby providing a convenient parameter by which to determine level or flow. Level or flow is determined by dividing the difference in the voltages across the hot and cold sensors by the voltage across the cold sensor.

대표청구항 ▼

A thermoresistive sensor circuit for determining a parameter of a medium surrounding one or more sensors, comprising: a first sensor mounted in the medium, said first sensor having a resistance which varies with temperature; a second sensor mounted in the medium at a uniform depth with said first se

A thermoresistive sensor circuit for determining a parameter of a medium surrounding one or more sensors, comprising: a first sensor mounted in the medium, said first sensor having a resistance which varies with temperature; a second sensor mounted in the medium at a uniform depth with said first sensor, said second sensor having a resistance which varies with temperature; a first current source connected to said first sensor and applying a current (I1) through said first sensor, producing a first resistance RH and a first sensor voltage VH; a second current source connected to said second sensor and applying a current (I2) through said second sensor, producing a second resistance RC and second sensor voltage VC, said current (I2) being low enough to produce minimal self-heating of the second sensor; subtract means for subtracting one of said sensor voltages from the other, producing a difference voltage; and divide means for dividing said difference voltage by said second sensor voltage to produce a ratio that corresponds to a parameter of a medium; wherein said ratio is proportional to the difference between said first and second resistances RH and RC divided by the second resistance RC.