US 6,684,695 B1Granted

Mass flow sensor utilizing a resistance bridge

AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration

InventorsGustave C. Fralick, Danny P. Hwang, John D. Wrbanek

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Abstract

A mass flow sensor to be mounted within a duct and measures the mass flow of a fluid stream moving through the duct. The sensor is an elongated thin quartz substrate having a plurality of platinum strips extending in a parallel relationship on the strip, with certain of the strips being resistors connected to an excitation voltage. The resistors form the legs of a Wheatstone bridge. The resistors are spaced a sufficient distance inwardly from the leading and trailing edges of the substrate to lie within the velocity recovery region so that the measured flow is the same as the actual upstream flow. The resistor strips extend at least half-way through the fluid stream to include a substantial part of the velocity profile of the stream. Certain of the resistors detect a change in temperature as the fluid stream moves across the substrate to provide an output signal from the Wheatstone bridge which is representative of the fluid flow. A heater is located in the midst of the resistor array to heat the air as it passes over the array.

Claims21

Dependent claims

A sensor for measuring the mass flow of a fluid stream moving through a chamber comprising:

a thermal insulating substrate projecting into the chamber and extending in the direction of the fluid stream whereby said fluid stream flows past said substrate, said substrate having a leading and a trailing edge;
spaced first and second resistors on the substrate, said first resistor being located upstream in the fluid stream from the second resistor;
spaced third and fourth spaced resistors on the substrate, said third resistor being located upstream in the fluid stream from the fourth resistor;
said first, second, third and fourth resistors being located on said substrate a sufficient distance inwardly from the leading and trailing edges and having a height H approximately one-half or greater than the height of the fluid stream to be within the velocity recovery region of the fluid stream and to be subjected to nearly the entire velocity profile of the fluid stream as the stream moves across the resistors and past the substrate;
means for changing the temperature of the fluid stream as it passes between the first and second resistors and between the third and fourth resistors;
a Wheatstone bridge circuit having first, second, third and fourth legs, each of said legs containing a respective one of the first, second, third and fourth resistors;
and
an external circuit connected to the Wheatstone bridge circuit for receiving a signal from the Wheatstone bridge circuit and for developing an output signal indication of the fluid stream flowing through the chamber.

5 more elements

In combination, a fluid duct and a sensor mounted in said duct for measuring the mass flow of a fluid stream moving through said duct and past said sensor, said combination comprising:

a thermal insulating substrate projecting into the duct, said substrate having opposed sides and trailing and leading edges, said sides extending in the direction of the fluid stream whereby said fluid stream flows past said sides of the substrate;
spaced first and second resistors on the substrate, said first resistor being located upstream in the fluid stream from the second resistor;
spaced third and fourth spaced resistors on the substrate, said third resistor being located upstream in the fluid stream from the fourth resistor;
said first, second, third and fourth resistors being located on said substrate a sufficient distance inwardly from the leading and trailing edges and having a height H approximately one-half or greater than the height of the fluid stream to be within the velocity recovery region of the fluid stream and to be subjected to nearly the entire velocity profile of the fluid stream as the stream moves across the resistors and past the substrate;
means for changing the temperature of the fluid stream as it passes between the first and second resistors and between the third and fourth resistors;
a Wheatstone bridge circuit having first, second, third and fourth legs, each of said legs consisting of a respective one of the first, second, third and fourth resistors;
and
an external circuit connected to the Wheatstone bridge circuit for receiving a signal from the Wheatstone bridge circuit and for developing an output signal indication of the fluid stream flowing through the chamber.

5 more elements

Dependencies are inferred from the claim text.