Thermistor flow sensor and related method
AssigneePacesetter, Inc.
InventorHerman L. Renger
Life of this patent
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Abstract
A fluid flow rate measuring apparatus having a thermistor exposed to a flow of fluid and a driver circuit operable in an initial constant-voltage mode, in which it applies a substantially constant voltage across the thermistor, and a subsequent constant-current mode, in which it applies a substantially constant current through the thermistor, such current corresponding to the current level at the end of the constant-voltage mode. A voltage sensor measures the resultant voltage drop across the thermistor, which is a direct measurement of the fluid flow rate and which is substantially insensitive to variations in ambient temperature.
Claims12
A fluid flow measuring apparatus comprising:
- a thermistor having an electrical resistance that varies with temperature, the thermistor being exposed to a flow of fluid;
- a driver circuit operable in an initial constant-voltage mode and a subsequent constant-current mode, wherein in the initial constant-voltage mode the driver circuit applies a prescribed substantially constant voltage across the thermistor, to produce an electrical current that varies according to the temperature of the thermistor, and wherein in the subsequent constant-current mode the driver circuit applies a substantially constant current through the thermistor that corresponds to the current conducted at the end of the constant-voltage mode, wherein the resulting change in voltage across the thermistor is indicative of the fluid flow rate;
- and
- a voltage sensor that measures the voltage across thermistor during the constant-current mode and thereby determines fluid flow rate.
Apparatus associated with a device implantable in a patient, for measuring blood flow rate, comprising:
- a thermistor having an electrical resistance that varies with temperature, the thermistor being disposed within a blood vessel and exposed to a flow of blood;
- a driver circuit operable in an initial constant-voltage mode and a subsequent constant-current mode, wherein in the initial constant-voltage mode the driver circuit applies a prescribed substantially constant voltage across the thermistor, to produce an electrical current that varies according to the temperature of the thermistor, and wherein in the subsequent constant-current mode the driver circuit applies a substantially constant current through the thermistor that corresponds to the current conducted at the end of the constant-voltage mode, wherein the resulting change in voltage across the thermistor is indicative of the blood flow rate;
- and
- a voltage sensor that measures the voltage across the thermistor during the constant-current mode and determines the blood's flow rate.
A method for use in a device implantable in a patient, for measuring blood flow rate, comprising:
- implanting a thermistor in a blood vessel of a patient, in a position where it is exposed to a flow of blood, the thermistor having an electrical resistance that varies with temperature;
- applying a substantially constant voltage across the thermistor for a first time interval, to produce an electrical current that varies according to the temperature of the thermistor;
- subsequently conducting a predetermined current through the thermistor for a second time interval, such current corresponding to the current conducted at the end of the first time interval;
- and
- measuring the voltage drop across the thermistor at the end of the second time interval, to determine blood flow rate.
Dependencies are inferred from the claim text.