Hot film fluid flowmeter with auxiliary flow sensing

Claim 2

A fluid flowmeter comprising: means defining a main passage for the flow of a fluid therethrough; means defining a secondary passage extending substantially parallel to said main passage and including an inlet for receiving a portion of the fluid flowing in said main passage, a throat and an outlet for discharging the portion back into the main passage; means defining a tertiary passage fluidly interconnecting said throat and a point in said main passage displaced from said throat; and a constant temperature thermal anemometer operative to monitor the rate of flow of fluid flowing in said tertiary passage and to generate a total flow rate output signal as a function thereof.

Claim 3

The fluid flowmeter of claim 1, wherein said means defining a main passage includes a central axis, said fluid flowmeter further comprising means operative to receive at least a portion of the remaining fluid in said main passage and impart motion thereto about said axis for creating a reduced pressure area at the outlet of said secondary passage.

Claim 4

The fluid flowmeter of claim 2, wherein said means operative to receive said remaining fluid comprises a set of swirl vanes radially disposed within said main passage at an angle oblique to the flow direction of said remaining fluid.

Claim 5

The fluid flowmeter of claim 1, wherein said secondary passage comprises a venturi.

Claim 6

The fluid flowmeter of claim 1, wherein said anemometer comprises ambient temperature compensation means.

Claim 7

The fluid flowmeter of claim 5, wherein said ambient temperature compensation means comprises a fluid temperature sensing probe disposed within said tertiary passage.

Claim 8

The fluid flowmeter of claim 1, further comprising means operative to selectively restrict fluid flow through said tertiary passage.

Claim 9

The fluid flowmeter of claim 7, wherein said flow restriction means comprises a needle valve.

Claim 10

The fluid flowmeter of claim 1, wherein said point in said main passage is upstream of said throat.

Claim 11

The fluid flowmeter of claim 1, wherein said anemometer comprises a hot film resistance probe disposed within said tertiary passage.

Claim 12

The fluid flowmeter of claim 10, wherein said probe comprises: an electrically insulative substrate disposed within said tertiary passage a resistive coating carried by and substantially covering said substrate; and a pair of leads operatively connected to said coating to direct an electric current therethrough.

Claim 13

The fluid flowmeter of claim 11, wherein said coating is segmented and further comprises means operative to electrically bridge said segments for the flow of said current therebetween.

Claim 14

A fluid flowmeter comprising: means defining a main passage for the flow of a fluid therethrough and including a central axis; means defining a secondary passage extending substantially parallel to an axis defined by said main passage, said secondary passage including an inlet for receiving a portion of the fluid flowing in said main passage, a throat and an outlet for discharging the portion back into the main passage; means defining a tertiary passage fluidly interconnecting said throat and a point axially displaced from said throat for the aspiration of a fluid sample therethrough; a temperature dependent resistance element for sensing the rate of flow of said sample while within said tertiary passage; and means operative to establish an electric current within said element and to modulate said current to maintain said element at a substantially constant temperature whereby the extent of said modulation is representative of total fluid flow through said main passage.

Claim 15

A fluid flowmeter comprising: means defining a main passage for the flow of a fluid therethrough and including a central axis; means defining a secondary passage extending substantially parallel to an axis defined by said main passage, said secondary passage including an inlet for receiving a portion of the fluid flowing in said main passage, a throat and an outlet for discharging the portion back into the main passage; means defining a tertiary passage fluidly interconnecting said throat and a point axially displaced from said throat for the aspiration of a fluid sample therethrough; a temperature dependent resistance element for sensing the rate of flow of said sample while within said tertiary passage; and means operative to establish an electric current within said element and to modulate said current to maintain said element at a substantially constant temperature whereby the extent of said modulation is representative of total fluid flow through said main passage.

Claim 16

The fluid flowmeter of claim 13, further comprising means operative to receive at least a portion of the remaining fluid in said main passage and impart motion thereto about said axis for creating a reduced pressure area at the outlet of said secondary passage.

Claim 17

The fluid flowmeter of claim 14, wherein said means operative to receive said remaining fluid comprises a set of swirl vanes radially disposed within said main passage at an angle oblique to the flow direction of said remaining fluid.

Claim 18

The fluid flowmeter of claim 13, wherein said secondary passage comprises a venturi.

Claim 19

The fluid flowmeter of claim 13, wherein said means operative to establish an electric current further comprises ambient temperature compensation means.

Claim 20

The fluid flowmeter of claim 17, wherein said ambient temperature compensation means comprises a fluid temperature sensing probe disposed within said tertiary passage.

Claim 21

The fluid flowmeter of claim 13, further comprising means operative to selectively restrict fluid flow through said tertiary passage.

Claim 22

The fluid flowmeter of claim 19, wherein said flow restriction means comprises a needle valve.

Claim 23

The fluid flowmeter of claim 13, wherein said point in said main passage is upstream of said throat.

Claim 24

The fluid flowmeter of claim 13, wherein said temperature dependent resistance element comprises a hot film probe disposed within said tertiary passage.

Claim 25

The fluid flowmeter of claim 22, wherein said probe comprises: an electrically insulative substrate disposed within said tertiary passage a resistive coating carried by and substantially covering said substrate; and a pair of leads operatively connected to said coating to direct an electric current therethrough.

Claim 26

The fluid flowmeter of claim 23, wherein said coating is segmented and further comprises means operative to electrically bridge said segments for the flow of said current therebetween.

Claim 27

A fluid flowmeter comprising: a housing defining a main passage for the flow of a fluid therethrough and including a central axis; a venturi disposed substantially concentrically within said main passage and comprising a converging inlet for receiving only a portion of the fluid flowing in said main passage, a throat and a diverging outlet for discharging the portion back into the main passage; a tertiary passage disposed externally of said main passage and including an inlet in fluid communication with said main passage at a point upstream of said throat and an outlet in fluid communication with said throat; a plurality of circumferentially spaced swirl vanes radially interconnecting said housing and venturi at an angle oblique to said axis, said swirl vanes collectively operative to receive at least a portion of the remaining fluid in said main passage and impart motion thereto about said axis for creating a reduced pressure area at the outlet of said venturi; and a constant temperature thermal anemometer operative to monitor the rate of flow of fluid flowing in said tertiary passage and to generate a total flow rate output signal as a function thereof, said anemometer comprising; a four element resistance bridge circuit, one of said elements comprising a temperature dependant resistor disposed within said tertiary passage for impingement of said fluid thereon, and an active power supply operative to establish an electric current within said resistor, to modulate said current to maintain said resistor at a substantially constant temperature to offset the cooling effect of the fluid impinging thereon, and to generate said signal in proportion to the extent of said modulation.

Claim 28

A fluid flowmeter comprising: a housing defining a main passage for the flow of a fluid therethrough and including a central axis; a venturi disposed substantially concentrically within said main passage and comprising a converging inlet for receiving only a portion of the fluid flowing in said main passage, a throat and a diverging outlet for discharging the portion back into the main passage; a tertiary passage disposed externally of said main passage and including an inlet in fluid communication with said main passage at a point upstream of said throat and an outlet in fluid communication with said throat; a plurality of circumferentially spaced swirl vanes radially interconnecting said housing and venturi at an angle oblique to said axis, said swirl vanes collectively operative to receive at least a portion of the remaining fluid in said main passage and impart motion thereto about said axis for creating a reduced pressure area at the outlet of said venturi; and a constant temperature thermal anemometer operative to monitor the rate of flow of fluid flowing in said tertiary passage and to generate a total flow rate output signal as a function thereof, said anemometer comprising; a four element resistance bridge circuit, one of said elements comprising a temperature dependant resistor disposed within said tertiary passage for impingement of said fluid thereon, and an active power supply operative to establish an electric current within said resistor, to modulate said current to maintain said resistor at a substantially constant temperature to offset the cooling effect of the fluid impinging thereon, and to generate said signal in proportion to the extent of said modulation.

Claim 29

The fluid flowmeter of claims 1, 13 or 25, wherein said tertiary passage further comprises an intermediate portion extending upstream of said point.