Abstract: An apparatus is provided for determining the mass flow rate of a fluid using thermal means. The apparatus utilizes resistance temperature detectors having substantially linear temperature dependencies to determine the mass flow rate of a fluid. The apparatus maintains a constant ratio between resistances of the first and second resistance temperature detectors, the amount of current necessary to maintain the constant ratio corresponding to the mass flow rate of the fluid. The apparatus includes a microprocessor wherein an algorithm relating the current and mass flow rate including thermophysical properties of the fluid, sensor thermal resistance, and probe stem loss information provides the fluid mass flow rate based upon calibration information. Operation in alternate fluids without the need for recalibration is possible utilizing calibration constants obtained in the primary fluid and substitution of thermophysical properties and stem loss characteristics of each fluid in which operation is desired.

Abstract: 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.

Abstract: A thermoresistive sensor system compensates for ambient temperature of a medium. First and second side-by-side sensors are mounted in the medium, each having a resistance that varies with temperature change in the medium. A thermal compensation control circuit supplies current to the first sensor such that the cube of its current times its resistance (I.sub.1.sup.3 .times.R.sub.1) is constant. The control circuit supplies current to the second sensor at a multiple of the current through the first sensor. A signal based upon the voltages across each sensor is produced as a temperature compensated output. In this manner, the system automatically compensates for temperature changes in the medium which would otherwise degrade the accuracy of the output.

Abstract: A constant power thermal property sensor compensates for changes in the temperature of the medium into which the sensor is disposed. The sensor has two side-by-side probes mounted in the medium with resistances that vary with temperature. A constant power source produces a current through the first probe and a current source applies a current to the second probe at a fixed ratio of the current in the first probe. The voltages across the probes are monitored and compared, and a signal is produced which is divided by current through the first probe. The resulting signal is representative of the heat transfer between the probes and the medium. The signal does not appreciably vary with changes in the temperature of the medium, and the medium may be a liquid, a gas, a liquid flow, a gas flow, or a combination of media. In this construction, two principal applications for the sensor are liquid level detectors and flow monitors.

Abstract: A probe for measuring heat includes an elongate rod fitted within a sheath, and a plurality of annular recesses are formed on the surface of the rod in a spaced-apart relationship to form annular chambers that are resistant to heat flow. A longitudinal bore extends axially into the rod and within the cylinders defined by the annular chambers, and an integrated heater and thermocouple pack is dimensioned to fit within the bore. In construction, the integrated pack includes a plurality of wires disposed in electrical insulation within a sheath and a heater cable. These wires include one common wire and a plurality of thermocuple wires. The common wire is constructed of one type of conductive material while the thermocouple wires are each constructed of two types of materials so that at least one thermocouple junction is formed therein. All of the wires extend the length of the integrated pack and are connected together at their ends.

Abstract: A probe for measuring heat includes an elongate rod fitted within a sheath, and a plurality of annular recesses are formed on the surface of the rod in a spaced-apart relationship to form annular chambers that are resistant to heat flow. A longitudinal bore extends axially into the rod and within the cylinders defined by the annular chambers, and an integrated heater and thermocouple pack is dimensioned to fit within the bore. In construction, the integrated pack includes a plurality of wires disposed in electrical insulation within a sheath and a heater cable. These wires include one common wire and a plurality of thermocouple wires. The common wire is constructed of one type of conductive material while the thermocouple wires are each constructed of two types of materials so that at least one thermocouple junction is formed therein. All of the wires extend the length of the integrated pack and are connected together at their ends.