초록 ▼

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

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.

대표청구항 ▼

An autoreferencing liquid level sensing apparatus comprising: a temperature sensitive resistance element including a silicon bulk resistor element having an impurity concentration level for causing said silicon bulk resistor element to exhibit a positive temperature coefficient of resistance within

An autoreferencing liquid level sensing apparatus comprising: a temperature sensitive resistance element including a silicon bulk resistor element having an impurity concentration level for causing said silicon bulk resistor element to exhibit a positive temperature coefficient of resistance within a predetermined temperature range and first and second electrodes in ohmic contact with said silicon bulk resistor, said temperature sensitive resistance element being disposed at a position whereat the presence of a liquid is to be determined; a timing means for generating an enabling signal for a predetermined period of time; an electric power source connected to said temperature sensitive resistance element and said timing means for applying a predetermined amount of electric power to said temperature sensitive resistance element via said first and second electrodes when said enabling signal is generated; a resistance measuring means connected to said temperature sensitive resistance element for generating a temperature dependent signal corresponding to the electrical resistance of said temperature sensitive resistance element; a temperature reference means connected to said timing means and said reference measuring means for generating a temperature reference signal having an initial value and a rate of change, each related to the temperature dependent signal at the beginning of said predetermined period of time; a comparison means connected to said resistance measuring means and said temperature reference means for generating a comparison output signal whenever said temperature dependent signal and said temperature reference signal have a predetermined relationship; and a latch means connected to said timing means and said comparison means for generating a latch output signal if said enabling signal and said comparison output signal are ever generated simultaneously.