Pulsed thermal flow sensor system
First Claim
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1. An apparatus for measuring fluid flow comprising:
- a substrate defining in its principal surface a conduit for flow of a fluid;
a first heating element for heating said fluid being inside said conduit;
at least two spaced-apart sensors being inside said conduit and positioned downstream of said heating element with respect to a direction of the flow for sensing a temperature of the fluid; and
at least one additional heating element located on said principal surface and not in contact with said conduit, said additional heating element being electrically identical to said first heating element; and
means for connecting said first heating element and said additional heating element in a bridge circuit.
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Abstract
A precise fluid flow meter fabricated by micromachining techniques measures a wide range of fluid flow rates. Two serial portions of an enclosed channel have different cross-sectional areas, and therefore different flow velocities. The fluid carries the thermal pulse through the flow channel to two sensor elements spaced apart along the channel downstream from the heating element. The transit time of the thermal pulse between the two sensor elements measures the fluid flow velocity.
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Citations
7 Claims
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1. An apparatus for measuring fluid flow comprising:
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a substrate defining in its principal surface a conduit for flow of a fluid; a first heating element for heating said fluid being inside said conduit; at least two spaced-apart sensors being inside said conduit and positioned downstream of said heating element with respect to a direction of the flow for sensing a temperature of the fluid; and at least one additional heating element located on said principal surface and not in contact with said conduit, said additional heating element being electrically identical to said first heating element; and means for connecting said first heating element and said additional heating element in a bridge circuit. - View Dependent Claims (2, 3, 4, 5)
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6. A method of measuring a fluid flow rate through a conduit, comprising the steps of:
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introducing a heat pulse into the fluid at a first location along said conduit; measuring a temperature of said fluid at a second location along said conduit downstream of said first location and observing a first time when a first temperature is attained; measuring a temperature of said fluid at a third location along said conduit downstream by a particular distance from said second location and observing a second time when a second temperature is attained; determining the fluid flow rate as a function of the first and second observed times and said particular distance; measuring an abrupt decrease in heat dissipation at said first location; and in response, reducing an amount of power used to provide heat at said first location. - View Dependent Claims (7)
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Specification