Detecting method and apparatus using heat sensitive devices
First Claim
1. A method for detecting fluid flow comprising, a pair of electrically heated matched temperature sensitive devices, one of said devices being positioned in the flowing fluid to be measured and one of said devices being positioned out of the fluid flow at a thermal reference location wherein a change in the flow rate results in change in the ratio of dissipation coefficients of said devices, a method for indicating the change in the ratio of dissipation coefficient which is insensitive to variation in ambient temperature, said method comprising, maintaining the temperature of the two devices substantially equal, and detecting changes in the ratio of the power dissipation in one device with respect to the power dissipation in the other, wherein a change in said power dissipation ratio indicates a change in the dissipation coefficient ratio.
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Abstract
This invention relates generally to the sensing of phenomena using heat sensitive devices. More particularly, the invention relates to an improved method and system wherein the ratio of the dissipation coefficients of a pair of electrically heated matched temperature sensitive devices is detected, which method and system are insensitive to variation in ambient temperature.
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Citations
15 Claims
- 1. A method for detecting fluid flow comprising, a pair of electrically heated matched temperature sensitive devices, one of said devices being positioned in the flowing fluid to be measured and one of said devices being positioned out of the fluid flow at a thermal reference location wherein a change in the flow rate results in change in the ratio of dissipation coefficients of said devices, a method for indicating the change in the ratio of dissipation coefficient which is insensitive to variation in ambient temperature, said method comprising, maintaining the temperature of the two devices substantially equal, and detecting changes in the ratio of the power dissipation in one device with respect to the power dissipation in the other, wherein a change in said power dissipation ratio indicates a change in the dissipation coefficient ratio.
- 5. A system for detecting fluid flow comprising, a pair of electrically heated matched temperature sensitive devices, one of said devices being positioned in the flowing fluid to be measured and one of said devices being positioned out of the fluid flow at a thermal reference location wherein a change in the flow rate results in change in the ratio of dissipation coefficients of said devices, means for indicating the change in the ratio of dissipation coefficients which are insensitive to variation in ambient temperature, said indicating means comprising, means for maintaining the temperature of the two devices substantially equal, and means for detecting changes in the ratio of the power dissipation in one device with respect to the power dissipation in the other wherein a change in said power dissipation ratio indicates a change in the dissipation coefficient ratio.
- 9. A fluid flow detecting system comprising, a pair of electrically heated matched temperature sensitive devices, one of said devices being positioned in the flowing fluid to be measured and one of said devices being positioned out of the fluid flow at a thermal reference location, wherein a change in the flow rate results in a change in the ratio of dissipation coefficients of said devices, means coupled to each of said devices for maintaining said two devices at substantially equal temperature, and means for detecting changes in the ratio of the power dissipation in one device with respect to the power dissipation in the other, wherein a change in said power dissipation ratio indicates a change in the dissipation coefficient ratio which is insensitive to variation in ambient temperature.
- 13. In an anesthesiology system in which a pump provides a flow of gases to a gas analyzer, a servo system for controlling the flow rate of the pump, said servo system including a pair of electrically heated matched temperature sensitive devices, one of said devices being positioned in the flowing gases to the gas analyzer and one of said devices being positioned out of the gas flow at a thermal reference location, means coupled to each of said devices for maintaining said two devices at substantially equal temperature, means for detecting the ratio of the power dissipation in one device with respect to the power dissipation in the other, wherein a change in said power dissipation ratio indicates a change in the dissipation coefficient ratio which is insensitive to variation in ambient temperature, and means responsive to the detected ratio for controlling the pump rate to maintain a constant flow rate.
Specification