Abstract: An autoreferencing liquid level sensing apparatus and method determines the presence of a liquid by observation of the convective cooling rate of a heated temperature sensor. The temperature measured by the temperature sensor is compared with an adapting temperature reference whose initial value is determined from the initial measured temperature and whose value increases during the heating at a rate proportional to the rate of heating of the temperature sensor and the initial temperature. This comparison enables discrimination of whether the convective cooling rate of the temperature sensor is above or below a predetermined level. Because the rate of convective cooling depends in large part on the thermal capacity of the fluid surrounding the sensor, the convective cooling rate determination allows discrimination of whether the temperature sensor is surrounded by a gas or a liquid, or surrounded by one of two immiscible liquids having differing thermal properties.

Abstract: A silicon temperature sensitive resistive element for employment as a convective cooling rate sensor. The convective cooling rate sensor comprises a small chip of silicon having an impurity ion cncentration level high enough to assure that the sensor exhibits an extrinsic positive temperature coefficient of resistance throughout a desired temperature range. The silicon chip is connected to a pair of metal electrodes. These metal electrodes have a cross-sectional area providing a desired rate of conductive cooling through these electrodes. A predetermined amount of electrical power is applied to the convective cooling rate sensor via the electrodes to cause ohmic self-heating of the sensor. The temperature of the sensor is determined by measuring the resistance of the sensor. The rate of temperature change is indicative of the rate of convective cooling of the sensor by the medium surrounding the sensor.

Abstract: A semiconductor pressure sensor employing the piezoresistive effect of single crystal silicon resistors to measure the flexure of a semiconductor diaphragm. In the preferred embodiment, a Wheatstone bridge composed of a first pair of resistors disposed on the center of the diaphragm and a second pair of resistors disposed on the periphery of the diaphragm is employed. Due to the nature of the diaphragm flexure, the first and second pairs of resistors exhibit piezoresistivity in opposite directions enabling pressure measurement with greater sensitivity. The diaphragm is mounted on and supported by a silicon clamp ring. The diaphragm and the clamp ring together form a unitary semiconductor structure.

Abstract: An automated fluid flow measurement system employs two temperature sensitive silicon resistors having tracking temperature coefficients. The resistors have equal impurity concentration but different values of resistance. The first temperature sensitive resistor is employed to measure the temperature of a flowing fluid. The second temperature sensitive resistor is electrically heated to a temperature at a predetermined amount greater than the measured temperature of the fluid. Because the rate of heat transfer from the heated temperature sensitive resistor to the fluid depends upon the rate at which the fluid passes this temperature sensitive resistor, the power required in order to maintain the predetermined temperature difference in the second temperature sensitive resistor is a measure of the flow rate of the fluid.