The patent's assignee for patent number 8650946 is
News editors obtained the following quote from the background information supplied by the inventors: "Background Information
"Fluid flow rates are often measured using sensors that introduce flow impedance. For example, differential pressure flowmeters, vortex meters, turbine meters, moving target meters and various other sorts of flow meters configured as probes all restrict flow and thereby provide a flow impedance that is an inherent feature of the sensor itself.
"In a case of particular interest, a differential pressure sensor senses a pressure difference caused by a flow obstruction, where the differential pressure is an indication of the fluid flow rate. The differential pressure sensor's output is a highly non-linear function of flow rate and is usable over a limited operating range. Differential pressure sensors are particularly inaccurate at very low flow rates. Thus, there is a need to enhance the linearity and accuracy of this type of sensor at lower portions of the flow range.
"A thermal flow sensor taught by the inventor in his U.S. Pat. No. 6,023,969 is responsive to only a cyclic component of a modulated flow. Because the cyclic component, aside from a possible offset introduced by fluid motion induced by the flow modulator itself, is zero when there is no flow, this sensor provides an accurate and stable zero. This sensor shares a common drawback of thermal flow sensors in that the presence of a contaminant film on a heated sensing element reduces accuracy at higher flow rates."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "One aspect of the invention is that it provides a composite apparatus for measuring a rate of flow of a fluid in a primary conduit in the neighborhood of a flow impedance. This apparatus comprises a first flow sensor that may include the flow impedance as an implicit feature of its installation in the primary conduit (e.g., the first flow meter may be a vortex or turbine meter). Alternately, an orifice plate or other flow restriction may be added to the primary conduit and the pressure drop across that restriction may be measured by a flow sensor that does not, of itself, add an appreciable flow impedance and (e.g., a differential pressure sensor) and that may require the addition of a separate element (e.g., an orifice plate) to provide the flow impedance. The first flow sensor is operable to provide a first measure of the rate of flow in the primary conduit. The apparatus also comprises a bypass conduit extending from a point upstream of the flow impedance to another point downstream of the flow impedance so that a pressure drop in the primary conduit causes fluid to flow through the bypass conduit. In addition there is a thermal flow sensor installed in the bypass conduit. The thermal flow sensor comprises at least one heated temperature sensitive element and a flow modulator operable to modulate flow in the bypass conduit to thereby cause the at least one temperature sensitive element to generate a cyclic signal indicative of heat removed by the flowing fluid. The cyclic signal is processed by signal processing circuitry that generates from it a second measure of the rate of flow in the primary conduit.
"Another aspect of the invention is that it combines a first flow measurement made by a flow sensor accurate at medium to high flow rates with a thermal flow measurement having a stable zero. This can provide an increased range of flows over which an accurate measurement can be made. In this combination a preferred thermal flow sensor is generally of the type described by the inventor in his U.S. Pat. No. 6,023,969, the teaching of which is herein incorporated by reference.
"A specific aspect of the invention is that it provides an apparatus for measuring the rate of flow of a fluid in a primary conduit by combining at least: a flow restriction; a differential pressure sensor; and a thermal flow sensor disposed in a bypass conduit extending between the two sensing surfaces of the differential pressure sensor. In this arrangement the differential pressure sensor provides a first measure of the rate of flow of fluid in the primary conduit from the pressure change associated with the restriction. The thermal flow sensor, which is characterized by very low zero drifts, comprises a flow modulator operable to modulate flow in the bypass conduit so as to cause at least one heated temperature sensitive element in the thermal sensor to generate a cyclic signal indicative of the amount of heat removed from it by the fluid flowing in the bypass conduit. This measurement can be extrapolated to provide a second measure of the rate of flow of fluid in the primary conduit.
"In a particular preferred embodiment, the invention provides an apparatus for measuring a rate of flow of a fluid in a primary conduit. This apparatus comprises: a flow restriction in the primary conduit; a differential pressure sensor arranged to sense a pressure differential caused by the flow restriction and to provide therefrom a first measure of the rate of flow in the primary conduit; a bypass conduit extending between the two sensing surfaces of the differential pressure sensor; and a thermal flow sensor for providing a second measure of the rate of flow. This thermal flow sensor comprises two heated temperature sensitive elements disposed in portions of the bypass conduit and exposed to a modulated flow which causes the two temperature sensitive elements to generate respective cyclic signals that are one hundred eighty degrees out of phase and which indicate the respective amounts of heat removed by the flowing fluid. The thermal flow sensor also comprises thermal flow signal processing circuitry operable to receive the cyclic signals and to generate from them a second measure of the rate of flow. In addition, the preferred apparatus comprises decision making circuitry having inputs from both the differential pressure sensor and from the signal processing circuitry. The decision making circuitry may be operable to construct a composite measurement of the rate of flow from the first and second measures thereof, or to select that one of the two measures that is known to be the more accurate indicator of the measured flow rate. Moreover one of the meters can be used to calibrate the other.
"It is yet a further aspect of the invention to combine a first flow measurement made in a primary conduit with a thermal flow measurement made in a bypass conduit that has an orifice, valve or other restriction in it. The flow restriction is preferably chosen to be small enough that little fluid flows through the bypass channel and the readings from the first flow sensor are nearly unaffected by the secondary flow. The restriction cuts the fluid flow increasingly as the flow rate increases and responds to increasing flow rates in a manner complementary to the response of the first flow sensor so that the two measurements can be combined to provide a response that is both more linear and that extends over a greater operating range. Note that the flow restriction in the bypass conduit can be located at a wide variety of locations within that conduit.
"A still further object of the invention is to provide a thermal flow sensor comprising thermal signal processing circuitry and a more efficient and economical cyclic flow modulator. The cyclic flow modulator may comprise a bifurcated flow channel; an electromechanical actuator; a movable perforate member; and two heated temperature sensitive elements. The perforate member is preferably movable by the electromechanical actuator to provide a maximum flow rate to a first portion of the bifurcated flow channel at the same time that it provides a minimum flow rate to the second portion of the bifurcated flow channel. The two heated temperature sensitive elements may be separately disposed to receive fluid flowing through the first and second bifurcated portions of the flow channel so as to generate respective cyclic signals indicative of respective amounts of heat removed therefrom by a flowing fluid.
"Those skilled in the art will recognize that the foregoing broad summary description is not intended to list all of the features and advantages of the invention. Both the underlying ideas and the specific embodiments disclosed in the following Detailed Description may serve as a basis for alternate arrangements for carrying out the purposes of the present invention and such equivalent constructions are within the spirit and scope of the invention in its broadest form. Moreover, different embodiments of the invention may provide various combinations of the recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments."
For additional information on this patent, see: Feller, Murray F. Thermal Flow Sensor Having an Electromagnetic Actuator for a Cyclic Flow Modulator. U.S. Patent Number 8650946, filed
Keywords for this news article include: Electronics,
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