CA1120286A - Directional heat loss anemometer transducer - Google Patents
Directional heat loss anemometer transducerInfo
- Publication number
- CA1120286A CA1120286A CA000352271A CA352271A CA1120286A CA 1120286 A CA1120286 A CA 1120286A CA 000352271 A CA000352271 A CA 000352271A CA 352271 A CA352271 A CA 352271A CA 1120286 A CA1120286 A CA 1120286A
- Authority
- CA
- Canada
- Prior art keywords
- wheatstone bridge
- series
- cylindrical
- electrical conductors
- conductors
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/10—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring thermal variables
- G01P5/12—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring thermal variables using variation of resistance of a heated conductor
Abstract
ABSTRACT
DIRECTIONAL HEAT LOSS
ANENOMETER TRANSDUCER
A directional heat loss anenometer transducer for sensing both the speed and direction of motion of a fluid, liquid or gas in which the transducer is immersed. The transducer is constructed of fine long cylindrical resistive conductors which are axially dis-posed about a central, cylindrical supporting body, wherein at least two conductors serve as a direction sensing pair which can also be used to determine impinging fluid speed. The sensing conductor pair are joined together by an adhesive connecting means thereby prevent-ing independent flow between the individual conductors of the conduct-or pair. The electrical conductors can be metallic or resistive films which are deposited on a cylindrical supporting body, or they may be individual wires of circular cross section. Each conductor is made of a material which exhibits a change in its electrical resistance as a function of temperature. Electrical connections are provided at each end of each conductor to permit each conductor to be separately excited by an electrical current. Typically, the transducer is oper-ated in air so as to provide a non-moving parts means for measuring a particular component of wind speed, and a pair of orthogonally mounted similar transducers can be used to determine sine and co-sine components of wind speed. Electrical representation of both speed and direction is obtained by the use of a differential amplifier which is connected between the joined conductor pair mid-point and the mid-point of a reference pair of resistors thereby forming a four arm resistance bridge. Direction sense is implicit in the sign of the differential amplifier output signal while speed is implicit in the mag-nitude of the differential amplifier output signal. The axis crossing, the point where direction sign changes polarity and the region where impinging flow is parallel to the long dimension of the conductor pair, is exceptionally smooth without discontinuities or irregularities.
DIRECTIONAL HEAT LOSS
ANENOMETER TRANSDUCER
A directional heat loss anenometer transducer for sensing both the speed and direction of motion of a fluid, liquid or gas in which the transducer is immersed. The transducer is constructed of fine long cylindrical resistive conductors which are axially dis-posed about a central, cylindrical supporting body, wherein at least two conductors serve as a direction sensing pair which can also be used to determine impinging fluid speed. The sensing conductor pair are joined together by an adhesive connecting means thereby prevent-ing independent flow between the individual conductors of the conduct-or pair. The electrical conductors can be metallic or resistive films which are deposited on a cylindrical supporting body, or they may be individual wires of circular cross section. Each conductor is made of a material which exhibits a change in its electrical resistance as a function of temperature. Electrical connections are provided at each end of each conductor to permit each conductor to be separately excited by an electrical current. Typically, the transducer is oper-ated in air so as to provide a non-moving parts means for measuring a particular component of wind speed, and a pair of orthogonally mounted similar transducers can be used to determine sine and co-sine components of wind speed. Electrical representation of both speed and direction is obtained by the use of a differential amplifier which is connected between the joined conductor pair mid-point and the mid-point of a reference pair of resistors thereby forming a four arm resistance bridge. Direction sense is implicit in the sign of the differential amplifier output signal while speed is implicit in the mag-nitude of the differential amplifier output signal. The axis crossing, the point where direction sign changes polarity and the region where impinging flow is parallel to the long dimension of the conductor pair, is exceptionally smooth without discontinuities or irregularities.
Description
~zoz~
TEC~INICAL FIELD
This invention relates generally to an improved anemom-eter sensing apparatus for determining the motion of a fluid mass which surrounds the transducer or, conversely, motion of the trans-ducer through the fluid. The invention is par~icularly concerned with a directional heat loss anemometer transducer for sensing both the speed and direction of motion of a fluid, as a liquid or a gas, in which the transducer is immersed.
BACKGROUND A~T
The use of hot wires and hot films as anemometer trans-ducers is well known in the prior art. Examples of prior art thermal anemometer sensors, and circuits therefor, are shown in U.S. Patent Nos. 3,138,025, 3,333,470, 3,352,15~, 3,604,261, 3,900,819 and 4,024,761. The present invention provides a significant improvement in the angular response or azimuth response of the transducer as well as a reduction in the excita-tion power which is needed to arrive at a useful operatingsensitivity level.
:`
Prior art transducers, which use no moving parts, have characteristically had some degree of difficulty in realizing a smooth and continuous transition from one direction to the opposite direction. The use of electrical "dither" signals and artificial "lobe switching" from side to side has helped to reduce axis crossing irregularities. Further improvement has been brought about by the use of a self-induced turbulent wake as a naturally occurring "dither" signal in the axis crossing regions.
:, DISCLOSURE OF THE INVENTION
,: .
~ The present invention uses a direction sensing pair of .
~ I~
, . . :.
.. : ;: : . - : .:
conductors which tal~es advantage of the naturally turbulent wake which occurs when virtually any interfering geometric body is placed in a moving fluid. By symmetrically arranging the sensing conduct-ors' geometric positioning, in respect to that body, an aerodynamic 5 "dither" signal is introduced into the direction sensor signal output for low angle flow, that is, flow which is nearly parallel to the sensing conductors' length. In effect, a variable amount of random turbulence is added to the output of the direction sensing pair of con-ductors as a function of incidence angle and speed of the impinging 10 fluid. The least turbulence is introduced for flow normal to the major axis of the transducer and lying in the plane which contains the parallel axes of the sensing conductors. A pronounced flow from one side or the other side, causes the self-generated turbu-lent wake to be swept away from the transducer elements. Down-15 ward flow over the support, or flow containing a vertical componentwill induce a turbulent wake across the sensing element which is away from the flow source, further aiding in smoothing the axis crossing response of the transducer.
The directional heat loss anemometer transducer of the 20 present invention includes at least two similar, thermally and physically separated, electrical conductors. Each of said electrical conductors has a length at least equal to the largest cross sec-tion dimension OI the conductor. In one type of embodiment of the in-vention, each of said electrical conductors includes a hollow, tubu-25 lar, electrically non-conductive refractory cylindrical substrate supporting body extending the length of the conductor, a conductive resistance film having a non-zero temperature coefficient of resis-tance adhered to the outer surface of the substrate body and extend-ing over the length of the substrate body, and an overall protective 30 coating which continuously extends over the outer surface of the conductive resistance film over the entire length of the conductive resistance film. In another type of embodiment the electrical con-ductors are wires, with solid or tubular cross sections. A cylin-drical support element is centrally disposed between and alongside 35 the two resistive electrical conductors. The cylindrical support may be straight, or it may have a straigm middle section and two right angled legs bent to form a U shape. The electrical conduc-tors are disposed as a pair, finitely separated, and mounted parallel to and in close proximity to -the straight, middle section 40 of the cylindrical support element. Connective bridging means is operatively disposed between said electrical conductors, where the plane containing the parallel central axes of the two conductors is perpendicular to the plane which is defined by the axis of said cylindrical support element. The bridging means closes the space -- .
-between said conductors, thereby preventillg connected flow com-pletely around one conductor of the pair o two conductors, inde-pendent of the other conductor. The two conductors are su,~ported in the protected lee o~ the cylindrical support element. Each of the , 5 electrical conductors is provided with electrical connection means, whereby each electrical conductor can be electrically heated by an electric current passed through each conductor. The electrical . conductors are attached to the cyLindrical support member by suit-; able attachment means. A modified embodiment of the invention may include a second similar cylind~ical support me.mber centrally disposed between and alongside the two electrical conductors, and situated on the side of the two electrical conductors opposite and '~ parallel to the first cylindrical support member .; , The present invention is further enhanced by the use of a 1;~ single differential amplifier which is used to read out the compo-site speed and direction signal from said electrical conductor pair when they are connected together with two reference resistors to form a four arm Wheatstone bridge. This connection provides the greatest accuracy of read out, together with providing means for 0 the electrical combining of mean impinging flow signals together with the support induced turbulence signals as an aid in smoothing the transducer's azimuth response.
While it will be apparent that the preferred embodiments of , -. the invention herein disclosed are well calculated to achieve the re-sults aforestated, it will be appreciated that the invention is suscep-tible to modification, variation and change.
.: .
BRIEF DESCRIPTION OF THE DRAWINGS `
Figure 1 is a Perspective view of a directional heat loss anemometer transducer made in accordance with the principles of 30 the present invention.
Fi~ure 2 is an elevational section view of the directional heat loss anemometer transducer structure illustraied in Figure 1, taken along the line 2-2 thereof, and looking in the direction of the arrows.
Figure 3 is a simplified electrical schematic drawing which illustrates excitation and read out means for a dual sensing element transducer of the type illustrated in Figure 1.
4 ~ 16 Figure 4 is an elevational section view, similar to Figure ~, and illustrating a second embodiment wherein the two sensing elements are wires rather than films.
Figure 5 is an elevational section view, similar to Figure 5 2, and illustrating a third embodiment wherein a second support mem-ber is mounted opposite to the first support member.
~EST MODE OF CARRYING OUT THE INVENTION
Referring now to the drawings, and in particular to Figure 1, the numeral 10 generally designates a directional heat loss ane-10 mometer transducer constructed in accordance with the principlesof the present invention. The transducer 10 includes two cylindrical, parallel sensing elements or members, generally indicated by the rumerals lla and llb, which are resistive sensing elements whose lengths are substantially greater than their diameters. Typically, 15 the sensing members lla and llb may have an outside diameter of 0, 6 mm, with an overall length of 25 mm, therefore having a length to diameter ratio of almost 42 to 1. As shown in Figures 1 and 2, the elements lla and llb are physically separated from each other, and they are joined or connected along their length by an adhesive 20 or oTher bridging means 12. The sensing elements lla and llb are similar in construction, and they are thermally separated.
The pair of sensing elements lla and llb are mounted be-low and parallel to a cylindrical support rnember, generally indi-cated by the numeral 15. Sensing element pair lla and llb is 25 attached to the cylindrical support member 15 by either adhesive or mechanical means 12a and 12b so that the geometric relationship between support member 15 and sensing elements lla and llb are maintained during all operating conditions. A semi-flexible adhes-ive such as "Rl~ a trademark) silicone rubber, Dow-Corning 30 #732, or non-brittle epoxy resin can be used, or a formed metal or plastic connection which anchors and attaches the sensing elements lla and llb firmly to support 15 can be employed. The bodies of the sensing elements lla and llb have electrical connective means 13a and 13b, respectively, and electrical connecting wires 17a and 35 17b, respectively, at one end thereof, and like connection means l~a and 14b, respectively, and connecting wires 16a and 16b, re-spectively, at the other end thereof.
The support member 15 is shown as a rigid, U-shaped wire which can be made from plated steel, stainless steel or other ' : : : ,. . .
.. ~
. . .
, cylindrical material. The support member 15 includes the central, cylindrical body portion 15a, and the two integral end mounting por-tions 15b and 15c. The end mounting portions 15b and 15c are dis-posed perpendicular to the central portion 15a. The end mounting portic)ns 15b and 15c support the transd-lcer 10 in an operative position. The bodies of the sensing elements lla and llb are uni-formly covered with a resistive film, and the connection means 13a, 13b, 14a and 14b are made of similar mater}al in order to avoid thermocouple junction effects, and thereby help to produce the low-1 0 est possible intrinsic electrical noise level of the transducer. The connecting lead wires 16a, 17a and 17b are also constructed of a material which is similar to that used by the end connection means 13a, 13b, 14a and 14b, in order to also produce the greatest signal to noise performance ratio, thereby permitting the greatest possible dynamic operating range. The material usually used is annealed platinum metal although other materials such as nickel can be used.
Alternative materials which may be used for the sensing elements lla and llb are described in U. S. patent No 3, 352, 154.
Figure 2 illustrates a typical cross section for a direc-tional heat loss anemometer transducer 10 of the construction shown in Figure 1. The relative size of the parts of the transducer 10 can be understood from the fact that the cross section of the support member central portion.15a is made to a scale such that the diame-ter thereof, as shown, is approximately 1, 6 to 1, 8 mm. As shown in Figure 2, the two sensing elements lla and llb are supported axially along the rigid support member cent ral portion 15a which can be made of steel, plated steel, stainless steel, plastic, or other rigid material which is shaped as shown in Figure 1, in order to provide means for mechanical mounting and support of the trans-ducer 10. The support member 15 also provides a means for aero-dynamically disturbing the end flow along the sensing elements lla and llb which are mounted directly within the U shape of the support member 15 and parallel to the long straight central section or cross bar 15a A typical diameter of the cross-section of the support rnember 15 is two or three or rnore times that of the sensing mem-bers lla and llb, and in the configuration shown in Figures 1 and 2, the diameter of elements lla and llb is about 0, 6 mm. The opera-tion of each conductor of the direction sensing pair of conductors lla and llb Wi~L be similar when incident flow is contained within dsO the plane described by the axis 21 of the U shape of the support member 15 which, in Figure 2, is shown to be a vertical plane.
As shown in Figure 2, the sensing element lla consists ~ , , :,` ` ;' ' ~ ~, ',; .. ',, :
of an electrically non-conductive, hollow, tubular, non-porous, dense aluminum oxide refractory fine cylindrical substrate body l~a, upon the surface of which is uniforrnly deposited by firing, sintering or other deposition means, a thin film or coating of 5 platinun~ metal l9a. The substrate supporting body 18a may be made from other suitable materials that are electrically non-conductiveJ such as aluminum silicate or anodized aluminum and other ceramic materials. If a loW t;emperature or room temper-ature deposition process is used, a plastic tubular substrate may 10 also be employed~ The coating l9a has a further layer 20a of fused silica, glass, aluminum oxide, "TEFLON" ( a trademark ) or other protective coating material which provides abrasion and wear pro-tection for the metal film 19a. TyE~ical dimensions for the substrate body 18a are a cylinder diarneter of 0, 6mm, with a bore diameter of 0, 3 mm, and a length of about 25 or 30 mm. The thickness of the metal l9a is typically in the order of 2 to 10 microns, and it can vary in accordance with the particular coating method which is used~
The sensing element llb is constructed the same as lla, and the same reference numerals have been used followed by the small 20 letter "b".
;
A detailed discussion of îilm materials and fill~ construc-tion techniques and methods can be found on pages 35S through 365 of a book entitled "Resistance Temperature Transducers", ~y Virgil A. Sandborn of Colorado State University, published in 1972 bSr the 25 Metrology Press, Fort Collins, Colorado.
As best seen in Figure 2~ cross flow between the sensing elements lla and llb is prevented by use of the connecting bridge 12.
The material for bridge 12 can be a flexible, thermally isolating, adhesive material, such as Dow-Corning silicone varnish or Dow-30 Corning ~732 silicone rubber adhesive, which serves to firmly bridgethe gap between sensing elements lla and llb. "TEFLON" ( a trade mar~;~ silicone resin or other low thermal conductivity bridge mater-ials may be used. If high thermal conductivity material is used, directional sensitivity may be substantially reduced.
As shown in Figure 2, the axis 21 of the central support portion 15a bisects the angle, ~, between sensing element axes 22a and 22b. Angle ~ should be large enough to prevent sensing ele-ment lla from becoming in contact with sensing element llb and should not exceed 60 to 70 degrees in order to prevent sensing ele-40 ments lla and llb from coming within the stagnation region of cen-lra suppolt 15a when it is ventilated by flow within the plane de-;' ' ,' ~ .
:
~ .
fined by the parallel axes of sensing elements lla and llb For the proportions shown, where the diameter of the central support por-tion 15a is about three times the diameter of sensing elements lla and llb, a useful value for ~ is about 25 to 30 degrees. Optimum performance is realized when ~ is an acute angle. Typically, the central support portion 15a is two to four times the diameter of the individual sensing elements lla and llb, in order to provide struc-tural rigidity and to generate a significant turbulent wake which passes over the sensing elements lla and llb when fluid flow passes 10 across the central support portion 15a against elements lla and llb The geometric relationship of the support with respect to the sens-ing elements lla and llb is maintained by the use of an adhesive or mechanical attachment, which can be placed at the end of the ele-ments lla and llb, or at the lead wires 16a and 16b, close to their 15 attachment point to elements lla and llb, as 12a and 12b. The Figure 2 illustration suggests adhesive attachment such as may be obtained by the use of "RTV" silicone rubber adhesive, or Dow-Corning X732, for example.
Typically, resistance of the platinum films l9a and l9b 20 for a transducer 10 of the scale indicated by the above, is in the
TEC~INICAL FIELD
This invention relates generally to an improved anemom-eter sensing apparatus for determining the motion of a fluid mass which surrounds the transducer or, conversely, motion of the trans-ducer through the fluid. The invention is par~icularly concerned with a directional heat loss anemometer transducer for sensing both the speed and direction of motion of a fluid, as a liquid or a gas, in which the transducer is immersed.
BACKGROUND A~T
The use of hot wires and hot films as anemometer trans-ducers is well known in the prior art. Examples of prior art thermal anemometer sensors, and circuits therefor, are shown in U.S. Patent Nos. 3,138,025, 3,333,470, 3,352,15~, 3,604,261, 3,900,819 and 4,024,761. The present invention provides a significant improvement in the angular response or azimuth response of the transducer as well as a reduction in the excita-tion power which is needed to arrive at a useful operatingsensitivity level.
:`
Prior art transducers, which use no moving parts, have characteristically had some degree of difficulty in realizing a smooth and continuous transition from one direction to the opposite direction. The use of electrical "dither" signals and artificial "lobe switching" from side to side has helped to reduce axis crossing irregularities. Further improvement has been brought about by the use of a self-induced turbulent wake as a naturally occurring "dither" signal in the axis crossing regions.
:, DISCLOSURE OF THE INVENTION
,: .
~ The present invention uses a direction sensing pair of .
~ I~
, . . :.
.. : ;: : . - : .:
conductors which tal~es advantage of the naturally turbulent wake which occurs when virtually any interfering geometric body is placed in a moving fluid. By symmetrically arranging the sensing conduct-ors' geometric positioning, in respect to that body, an aerodynamic 5 "dither" signal is introduced into the direction sensor signal output for low angle flow, that is, flow which is nearly parallel to the sensing conductors' length. In effect, a variable amount of random turbulence is added to the output of the direction sensing pair of con-ductors as a function of incidence angle and speed of the impinging 10 fluid. The least turbulence is introduced for flow normal to the major axis of the transducer and lying in the plane which contains the parallel axes of the sensing conductors. A pronounced flow from one side or the other side, causes the self-generated turbu-lent wake to be swept away from the transducer elements. Down-15 ward flow over the support, or flow containing a vertical componentwill induce a turbulent wake across the sensing element which is away from the flow source, further aiding in smoothing the axis crossing response of the transducer.
The directional heat loss anemometer transducer of the 20 present invention includes at least two similar, thermally and physically separated, electrical conductors. Each of said electrical conductors has a length at least equal to the largest cross sec-tion dimension OI the conductor. In one type of embodiment of the in-vention, each of said electrical conductors includes a hollow, tubu-25 lar, electrically non-conductive refractory cylindrical substrate supporting body extending the length of the conductor, a conductive resistance film having a non-zero temperature coefficient of resis-tance adhered to the outer surface of the substrate body and extend-ing over the length of the substrate body, and an overall protective 30 coating which continuously extends over the outer surface of the conductive resistance film over the entire length of the conductive resistance film. In another type of embodiment the electrical con-ductors are wires, with solid or tubular cross sections. A cylin-drical support element is centrally disposed between and alongside 35 the two resistive electrical conductors. The cylindrical support may be straight, or it may have a straigm middle section and two right angled legs bent to form a U shape. The electrical conduc-tors are disposed as a pair, finitely separated, and mounted parallel to and in close proximity to -the straight, middle section 40 of the cylindrical support element. Connective bridging means is operatively disposed between said electrical conductors, where the plane containing the parallel central axes of the two conductors is perpendicular to the plane which is defined by the axis of said cylindrical support element. The bridging means closes the space -- .
-between said conductors, thereby preventillg connected flow com-pletely around one conductor of the pair o two conductors, inde-pendent of the other conductor. The two conductors are su,~ported in the protected lee o~ the cylindrical support element. Each of the , 5 electrical conductors is provided with electrical connection means, whereby each electrical conductor can be electrically heated by an electric current passed through each conductor. The electrical . conductors are attached to the cyLindrical support member by suit-; able attachment means. A modified embodiment of the invention may include a second similar cylind~ical support me.mber centrally disposed between and alongside the two electrical conductors, and situated on the side of the two electrical conductors opposite and '~ parallel to the first cylindrical support member .; , The present invention is further enhanced by the use of a 1;~ single differential amplifier which is used to read out the compo-site speed and direction signal from said electrical conductor pair when they are connected together with two reference resistors to form a four arm Wheatstone bridge. This connection provides the greatest accuracy of read out, together with providing means for 0 the electrical combining of mean impinging flow signals together with the support induced turbulence signals as an aid in smoothing the transducer's azimuth response.
While it will be apparent that the preferred embodiments of , -. the invention herein disclosed are well calculated to achieve the re-sults aforestated, it will be appreciated that the invention is suscep-tible to modification, variation and change.
.: .
BRIEF DESCRIPTION OF THE DRAWINGS `
Figure 1 is a Perspective view of a directional heat loss anemometer transducer made in accordance with the principles of 30 the present invention.
Fi~ure 2 is an elevational section view of the directional heat loss anemometer transducer structure illustraied in Figure 1, taken along the line 2-2 thereof, and looking in the direction of the arrows.
Figure 3 is a simplified electrical schematic drawing which illustrates excitation and read out means for a dual sensing element transducer of the type illustrated in Figure 1.
4 ~ 16 Figure 4 is an elevational section view, similar to Figure ~, and illustrating a second embodiment wherein the two sensing elements are wires rather than films.
Figure 5 is an elevational section view, similar to Figure 5 2, and illustrating a third embodiment wherein a second support mem-ber is mounted opposite to the first support member.
~EST MODE OF CARRYING OUT THE INVENTION
Referring now to the drawings, and in particular to Figure 1, the numeral 10 generally designates a directional heat loss ane-10 mometer transducer constructed in accordance with the principlesof the present invention. The transducer 10 includes two cylindrical, parallel sensing elements or members, generally indicated by the rumerals lla and llb, which are resistive sensing elements whose lengths are substantially greater than their diameters. Typically, 15 the sensing members lla and llb may have an outside diameter of 0, 6 mm, with an overall length of 25 mm, therefore having a length to diameter ratio of almost 42 to 1. As shown in Figures 1 and 2, the elements lla and llb are physically separated from each other, and they are joined or connected along their length by an adhesive 20 or oTher bridging means 12. The sensing elements lla and llb are similar in construction, and they are thermally separated.
The pair of sensing elements lla and llb are mounted be-low and parallel to a cylindrical support rnember, generally indi-cated by the numeral 15. Sensing element pair lla and llb is 25 attached to the cylindrical support member 15 by either adhesive or mechanical means 12a and 12b so that the geometric relationship between support member 15 and sensing elements lla and llb are maintained during all operating conditions. A semi-flexible adhes-ive such as "Rl~ a trademark) silicone rubber, Dow-Corning 30 #732, or non-brittle epoxy resin can be used, or a formed metal or plastic connection which anchors and attaches the sensing elements lla and llb firmly to support 15 can be employed. The bodies of the sensing elements lla and llb have electrical connective means 13a and 13b, respectively, and electrical connecting wires 17a and 35 17b, respectively, at one end thereof, and like connection means l~a and 14b, respectively, and connecting wires 16a and 16b, re-spectively, at the other end thereof.
The support member 15 is shown as a rigid, U-shaped wire which can be made from plated steel, stainless steel or other ' : : : ,. . .
.. ~
. . .
, cylindrical material. The support member 15 includes the central, cylindrical body portion 15a, and the two integral end mounting por-tions 15b and 15c. The end mounting portions 15b and 15c are dis-posed perpendicular to the central portion 15a. The end mounting portic)ns 15b and 15c support the transd-lcer 10 in an operative position. The bodies of the sensing elements lla and llb are uni-formly covered with a resistive film, and the connection means 13a, 13b, 14a and 14b are made of similar mater}al in order to avoid thermocouple junction effects, and thereby help to produce the low-1 0 est possible intrinsic electrical noise level of the transducer. The connecting lead wires 16a, 17a and 17b are also constructed of a material which is similar to that used by the end connection means 13a, 13b, 14a and 14b, in order to also produce the greatest signal to noise performance ratio, thereby permitting the greatest possible dynamic operating range. The material usually used is annealed platinum metal although other materials such as nickel can be used.
Alternative materials which may be used for the sensing elements lla and llb are described in U. S. patent No 3, 352, 154.
Figure 2 illustrates a typical cross section for a direc-tional heat loss anemometer transducer 10 of the construction shown in Figure 1. The relative size of the parts of the transducer 10 can be understood from the fact that the cross section of the support member central portion.15a is made to a scale such that the diame-ter thereof, as shown, is approximately 1, 6 to 1, 8 mm. As shown in Figure 2, the two sensing elements lla and llb are supported axially along the rigid support member cent ral portion 15a which can be made of steel, plated steel, stainless steel, plastic, or other rigid material which is shaped as shown in Figure 1, in order to provide means for mechanical mounting and support of the trans-ducer 10. The support member 15 also provides a means for aero-dynamically disturbing the end flow along the sensing elements lla and llb which are mounted directly within the U shape of the support member 15 and parallel to the long straight central section or cross bar 15a A typical diameter of the cross-section of the support rnember 15 is two or three or rnore times that of the sensing mem-bers lla and llb, and in the configuration shown in Figures 1 and 2, the diameter of elements lla and llb is about 0, 6 mm. The opera-tion of each conductor of the direction sensing pair of conductors lla and llb Wi~L be similar when incident flow is contained within dsO the plane described by the axis 21 of the U shape of the support member 15 which, in Figure 2, is shown to be a vertical plane.
As shown in Figure 2, the sensing element lla consists ~ , , :,` ` ;' ' ~ ~, ',; .. ',, :
of an electrically non-conductive, hollow, tubular, non-porous, dense aluminum oxide refractory fine cylindrical substrate body l~a, upon the surface of which is uniforrnly deposited by firing, sintering or other deposition means, a thin film or coating of 5 platinun~ metal l9a. The substrate supporting body 18a may be made from other suitable materials that are electrically non-conductiveJ such as aluminum silicate or anodized aluminum and other ceramic materials. If a loW t;emperature or room temper-ature deposition process is used, a plastic tubular substrate may 10 also be employed~ The coating l9a has a further layer 20a of fused silica, glass, aluminum oxide, "TEFLON" ( a trademark ) or other protective coating material which provides abrasion and wear pro-tection for the metal film 19a. TyE~ical dimensions for the substrate body 18a are a cylinder diarneter of 0, 6mm, with a bore diameter of 0, 3 mm, and a length of about 25 or 30 mm. The thickness of the metal l9a is typically in the order of 2 to 10 microns, and it can vary in accordance with the particular coating method which is used~
The sensing element llb is constructed the same as lla, and the same reference numerals have been used followed by the small 20 letter "b".
;
A detailed discussion of îilm materials and fill~ construc-tion techniques and methods can be found on pages 35S through 365 of a book entitled "Resistance Temperature Transducers", ~y Virgil A. Sandborn of Colorado State University, published in 1972 bSr the 25 Metrology Press, Fort Collins, Colorado.
As best seen in Figure 2~ cross flow between the sensing elements lla and llb is prevented by use of the connecting bridge 12.
The material for bridge 12 can be a flexible, thermally isolating, adhesive material, such as Dow-Corning silicone varnish or Dow-30 Corning ~732 silicone rubber adhesive, which serves to firmly bridgethe gap between sensing elements lla and llb. "TEFLON" ( a trade mar~;~ silicone resin or other low thermal conductivity bridge mater-ials may be used. If high thermal conductivity material is used, directional sensitivity may be substantially reduced.
As shown in Figure 2, the axis 21 of the central support portion 15a bisects the angle, ~, between sensing element axes 22a and 22b. Angle ~ should be large enough to prevent sensing ele-ment lla from becoming in contact with sensing element llb and should not exceed 60 to 70 degrees in order to prevent sensing ele-40 ments lla and llb from coming within the stagnation region of cen-lra suppolt 15a when it is ventilated by flow within the plane de-;' ' ,' ~ .
:
~ .
fined by the parallel axes of sensing elements lla and llb For the proportions shown, where the diameter of the central support por-tion 15a is about three times the diameter of sensing elements lla and llb, a useful value for ~ is about 25 to 30 degrees. Optimum performance is realized when ~ is an acute angle. Typically, the central support portion 15a is two to four times the diameter of the individual sensing elements lla and llb, in order to provide struc-tural rigidity and to generate a significant turbulent wake which passes over the sensing elements lla and llb when fluid flow passes 10 across the central support portion 15a against elements lla and llb The geometric relationship of the support with respect to the sens-ing elements lla and llb is maintained by the use of an adhesive or mechanical attachment, which can be placed at the end of the ele-ments lla and llb, or at the lead wires 16a and 16b, close to their 15 attachment point to elements lla and llb, as 12a and 12b. The Figure 2 illustration suggests adhesive attachment such as may be obtained by the use of "RTV" silicone rubber adhesive, or Dow-Corning X732, for example.
Typically, resistance of the platinum films l9a and l9b 20 for a transducer 10 of the scale indicated by the above, is in the
2 ohm to 6 ohm resistance range at room temperature. Optimum film resistance is best determined by the characteristics of the associated electronic controller which is used to excite the trans-ducer 10, and such factors as available power supply source, types 25 of amplifiers used, operating method selected, working fluid, and the lil~e, are all within the control of the instrument designer A large ratio of sensing element, lla and llb, length to element diameter will produce angular sensitivity to air~low or fluid flow as the flow vector moves away from normal flow which is 30 perpendicular to the cylindrical axes of elements lla and llb. ~;
Direction sensing is accomplished by sensing elements lla and llb as incident flow varies through 360 degrees in the plane contained by the parallel axes of sensing elements lla and llb. Direction sign sense can be determined by electrical measurement of the 35 change in relative resistance values of each sensing element lla and llb when they are compared with each other in a balanced bridge circuit. Fluid speed is determined bymeasurement of the magnitude of the differential signal which follows an approximate fourth root relationship to a speed increase.
Figu:re 3 illustrates a simplified schematic diagram of an electrical excitation and read out circuit which may be used to drive dual element transducers described by Figure 1. This circuit : .
provides both speed and directioïl signals fIom the driven tIanS-ducer as a con-~posite single output si~nal The sensing pair of elements lla and llb is shown connected as two arms of a four arm Wheatstone bridge which is also formed by resistors 23 and 2a~.
5 The resistors 23 and 24 are ~lsed to balance the bridge when the fluid medium surrounding the transducer is at rest or at zero speed.
Excitation to the bridge OI Figure 3 is provided at connections 25 and 26, and bridge balance betweerl points 27 and 23 is deLected and is amplified b~ a differential amplifier 29, ~thereby providing a signal 10 30 which is a measure of the degree oï imbalance of the direction bridge. The signal 30 shows imbalance by swinging to either posit-i~e or negative polarity when one or the other of the paired sensing elements lla or llb is ventilated at a greater speed by impinging fluid flow. The leeward or "down wind" element will "see" a lesser 15 flow speed because of the blocking which is caused by the other or "up wind" element. The magnitude of the resulting differential out-put signal 30 is a direct measure of speed. Resistors 31 and 33 are the input resistors to amplifier 29 and resistors 32 and 34 are the ~eedback resistors. Differential ga~n is set by the ratio of feedback 20 resistors 32 and 34 respectively to input resistors 31 and 33. Typic-al amplifier gain is in the range of twenty or twenty five for full scale air flow of, for example, 20 meters per second. The bridge formed by the resistors 23 and 21, together with the pair of sensing elements lla and llb can be considered to be electricall~ as a single 25 resistor which in turn becomes one arm of a second Wheatstone bridge which is formed by a power resistor 35 in series with the first Wheatstone bridge, or direction bridge, and by resistors 36 and 37 which are used to balance the second bridge at an operating point determined by the values of resisto rs 36 and 37. Either resis-30 tor 36 or 37 can be varied at the time of bridge design or a potentio-meter or variable resistor may be used for one or the other. It is preferred not to use potentiometers for both resistors. This allows operator sele ction of operating point, power level, and instrument sensitivity. Amplifier 38 is a high gain differential amplifier having 35 a high current output which is fed back in closed loop fashi on to the bridge at point 39. The input to amplifier 38 is taken across the bridge at points 26 and 40, and attention must be paid to phasing, in order to assure that negative feedback is used.
Sensing elements lla and llb, together with resistors 23 40 and 24, appear to amplifier 38 to function as a single resistance source which is sensitive to any variation in its constituent parts.
The sensing elements lla and llb are in fact non-zero temperature coefficient resistors which are subject to self-heating, and when platinum metal is used for the film, their temperature coefficient is a high positive value. This fact permits the setting of the values ,.
,, 9 ~ 6 of the r esistors 36 and 37 so that the bridge balance resistance values requi~ed or bridge balance are satisfied when the total series-parallel resistance of the directioll bridge, taken as a sing~le equivalent resistance, together with power resistor 35, both balance 5 against resistors 36 and 37 by having the same resistance ratios on either side of the bridge. The active side is comprised of resis-tor 35 together with the direc~:ion bridge, resistors lla and llb together with resistors 23 and 24. The reference side of the feed-back controlled bridge is comprised of resistors 36 and 37.
1~, When the ser.sing elemerlts lla and llb are c~ld or are non-operating, their resistance is lower than their operating value, and in controlling their operating value through the setting of the r eference resistance ratio, the heated r esistance values r equi r ed T.O self-balance the bridge can be selected, all of which is controlled 15 through means of negative feedbackthrough amplifier 38 back to the bridge at point 39. The feedback loop operates to aut~matically ~djust the current through the total combined bridges until the re-sistance of sensing elements lla and llb attains that value of resis-tance which balances the bridge. A small offset voltage must be _0 present at the output of amplifier 38 when the circuit is first turned on, and the sensing elements lla and llb are at ambient tempera-ture, so that the minute bridge current which flows as ~ result of the offset voltage is sufficient to develop a small error signal be-tween points 26 and 40, thus permitting the circuit to turn i-cself on 2;~ to an operating condition. The aforedescribed .mode of operation has been described as a constant temperature ( constant resistance ) method of hot film anemometer or hot wire anemometer operation.
Resistor 37 can be a temperature sensitive resistor which is physically located as to be exposed to the fluid ambient temper-30 ature. If the temperature coefficient of resistance of registor 37 isproperly selected the bridge operating level can be automatically ad-justed so that ambient temperature is tracked thereby operating the sensing elements lla and llb at a constant temperature difference above sensed ambient temperature. This mode of operation can pro-35 vide constant fluid speed sensitivity irrespective of changes inambi ent temp eratur e .
In a typical circuit, the resistance of each of the sensing elements lla and llb is 3. 3 ohms each at room temperature. The usual precautions must be observed when high temperature coeffic-40 ient resistors are measured at a particular temperature so thatmeasurement precision is preserved. The power resistor 35 is 2 ~ ~ . , .
: ~
. :: ' , :
~V2~
ohms and it has a low temperature coefficient of resistance, and adequate physical size, so that self-heating does not cause appreci-able change in its nominal resistance value with varying operating current levels. It must be observed that the full sensing element 5 operating current passes through resistor 35. For the transducer 10 of Figures 1 and 2, which is built to the scale indicated by the examples, typical zero speed current levels may be in the 0,1 ampere range, and at l~aximum flow, with current levels approach-ing one ampere for an e~;treme case. Resistor 36 is 499 ohms and 10 may be a precision film or precision wire-wound resistor. Values of resistors 23 and 24 are 10, 000 to 30, 000 ohms each, so as to avoid needless loading of the sensing elements lla and llb and re-sistors 23 and 24 are carefully matched so that with zero fluid flow conditions .the potentials at points 27 and 28 closely match thereby 15 providing a nulled Input to amplifier 29 producing a zero output at point 30 for zero fluid flow. A value of about 2, 245 ohms for re-sistor 37 will cause the direction bridge total resistance to r ise to 9 ohms~ thereby balancing the bridge. The resulting surface temper-ature of sensing elements lla and llb will be in tl~e 125 to 135 degree 20 Celsius range.
Output 30 is bipolar and indicates which sensing element, lla or llb, faces the impinging fluid flow. Thr sensing element facing the flow will be caused by cooling to be lower in resistance than the sensing element away from the flow which is cooled less 25 and which will increase in resistance while their total series resis-tance remains constant. The magnitude of output 30 is non-linear with reference to incident fluid speed and it indicates the amount of heat which is lost to the flowing mass of the fluid stream.
Amplifiers 29 and 38 can be integrated circuit operational 30 amplifiers which are operated from positive and negative 12 or 15 volt power sources. Fifteen volt operation can produce at least ten v olt signal swings at output 30. When two or more similar :I?igure
Direction sensing is accomplished by sensing elements lla and llb as incident flow varies through 360 degrees in the plane contained by the parallel axes of sensing elements lla and llb. Direction sign sense can be determined by electrical measurement of the 35 change in relative resistance values of each sensing element lla and llb when they are compared with each other in a balanced bridge circuit. Fluid speed is determined bymeasurement of the magnitude of the differential signal which follows an approximate fourth root relationship to a speed increase.
Figu:re 3 illustrates a simplified schematic diagram of an electrical excitation and read out circuit which may be used to drive dual element transducers described by Figure 1. This circuit : .
provides both speed and directioïl signals fIom the driven tIanS-ducer as a con-~posite single output si~nal The sensing pair of elements lla and llb is shown connected as two arms of a four arm Wheatstone bridge which is also formed by resistors 23 and 2a~.
5 The resistors 23 and 24 are ~lsed to balance the bridge when the fluid medium surrounding the transducer is at rest or at zero speed.
Excitation to the bridge OI Figure 3 is provided at connections 25 and 26, and bridge balance betweerl points 27 and 23 is deLected and is amplified b~ a differential amplifier 29, ~thereby providing a signal 10 30 which is a measure of the degree oï imbalance of the direction bridge. The signal 30 shows imbalance by swinging to either posit-i~e or negative polarity when one or the other of the paired sensing elements lla or llb is ventilated at a greater speed by impinging fluid flow. The leeward or "down wind" element will "see" a lesser 15 flow speed because of the blocking which is caused by the other or "up wind" element. The magnitude of the resulting differential out-put signal 30 is a direct measure of speed. Resistors 31 and 33 are the input resistors to amplifier 29 and resistors 32 and 34 are the ~eedback resistors. Differential ga~n is set by the ratio of feedback 20 resistors 32 and 34 respectively to input resistors 31 and 33. Typic-al amplifier gain is in the range of twenty or twenty five for full scale air flow of, for example, 20 meters per second. The bridge formed by the resistors 23 and 21, together with the pair of sensing elements lla and llb can be considered to be electricall~ as a single 25 resistor which in turn becomes one arm of a second Wheatstone bridge which is formed by a power resistor 35 in series with the first Wheatstone bridge, or direction bridge, and by resistors 36 and 37 which are used to balance the second bridge at an operating point determined by the values of resisto rs 36 and 37. Either resis-30 tor 36 or 37 can be varied at the time of bridge design or a potentio-meter or variable resistor may be used for one or the other. It is preferred not to use potentiometers for both resistors. This allows operator sele ction of operating point, power level, and instrument sensitivity. Amplifier 38 is a high gain differential amplifier having 35 a high current output which is fed back in closed loop fashi on to the bridge at point 39. The input to amplifier 38 is taken across the bridge at points 26 and 40, and attention must be paid to phasing, in order to assure that negative feedback is used.
Sensing elements lla and llb, together with resistors 23 40 and 24, appear to amplifier 38 to function as a single resistance source which is sensitive to any variation in its constituent parts.
The sensing elements lla and llb are in fact non-zero temperature coefficient resistors which are subject to self-heating, and when platinum metal is used for the film, their temperature coefficient is a high positive value. This fact permits the setting of the values ,.
,, 9 ~ 6 of the r esistors 36 and 37 so that the bridge balance resistance values requi~ed or bridge balance are satisfied when the total series-parallel resistance of the directioll bridge, taken as a sing~le equivalent resistance, together with power resistor 35, both balance 5 against resistors 36 and 37 by having the same resistance ratios on either side of the bridge. The active side is comprised of resis-tor 35 together with the direc~:ion bridge, resistors lla and llb together with resistors 23 and 24. The reference side of the feed-back controlled bridge is comprised of resistors 36 and 37.
1~, When the ser.sing elemerlts lla and llb are c~ld or are non-operating, their resistance is lower than their operating value, and in controlling their operating value through the setting of the r eference resistance ratio, the heated r esistance values r equi r ed T.O self-balance the bridge can be selected, all of which is controlled 15 through means of negative feedbackthrough amplifier 38 back to the bridge at point 39. The feedback loop operates to aut~matically ~djust the current through the total combined bridges until the re-sistance of sensing elements lla and llb attains that value of resis-tance which balances the bridge. A small offset voltage must be _0 present at the output of amplifier 38 when the circuit is first turned on, and the sensing elements lla and llb are at ambient tempera-ture, so that the minute bridge current which flows as ~ result of the offset voltage is sufficient to develop a small error signal be-tween points 26 and 40, thus permitting the circuit to turn i-cself on 2;~ to an operating condition. The aforedescribed .mode of operation has been described as a constant temperature ( constant resistance ) method of hot film anemometer or hot wire anemometer operation.
Resistor 37 can be a temperature sensitive resistor which is physically located as to be exposed to the fluid ambient temper-30 ature. If the temperature coefficient of resistance of registor 37 isproperly selected the bridge operating level can be automatically ad-justed so that ambient temperature is tracked thereby operating the sensing elements lla and llb at a constant temperature difference above sensed ambient temperature. This mode of operation can pro-35 vide constant fluid speed sensitivity irrespective of changes inambi ent temp eratur e .
In a typical circuit, the resistance of each of the sensing elements lla and llb is 3. 3 ohms each at room temperature. The usual precautions must be observed when high temperature coeffic-40 ient resistors are measured at a particular temperature so thatmeasurement precision is preserved. The power resistor 35 is 2 ~ ~ . , .
: ~
. :: ' , :
~V2~
ohms and it has a low temperature coefficient of resistance, and adequate physical size, so that self-heating does not cause appreci-able change in its nominal resistance value with varying operating current levels. It must be observed that the full sensing element 5 operating current passes through resistor 35. For the transducer 10 of Figures 1 and 2, which is built to the scale indicated by the examples, typical zero speed current levels may be in the 0,1 ampere range, and at l~aximum flow, with current levels approach-ing one ampere for an e~;treme case. Resistor 36 is 499 ohms and 10 may be a precision film or precision wire-wound resistor. Values of resistors 23 and 24 are 10, 000 to 30, 000 ohms each, so as to avoid needless loading of the sensing elements lla and llb and re-sistors 23 and 24 are carefully matched so that with zero fluid flow conditions .the potentials at points 27 and 28 closely match thereby 15 providing a nulled Input to amplifier 29 producing a zero output at point 30 for zero fluid flow. A value of about 2, 245 ohms for re-sistor 37 will cause the direction bridge total resistance to r ise to 9 ohms~ thereby balancing the bridge. The resulting surface temper-ature of sensing elements lla and llb will be in tl~e 125 to 135 degree 20 Celsius range.
Output 30 is bipolar and indicates which sensing element, lla or llb, faces the impinging fluid flow. Thr sensing element facing the flow will be caused by cooling to be lower in resistance than the sensing element away from the flow which is cooled less 25 and which will increase in resistance while their total series resis-tance remains constant. The magnitude of output 30 is non-linear with reference to incident fluid speed and it indicates the amount of heat which is lost to the flowing mass of the fluid stream.
Amplifiers 29 and 38 can be integrated circuit operational 30 amplifiers which are operated from positive and negative 12 or 15 volt power sources. Fifteen volt operation can produce at least ten v olt signal swings at output 30. When two or more similar :I?igure
3 bridge circuits are used, with an array of two or more trans-ducers, proper ground and power supply circuit wiring must be pro-35 vided in order to avoid unwanted cross taL~ between transducers andresulting faulure to operate properly. Amplifiers 29 and 38 can also be of a type which uses only a single power supply potential such as 15 or 20 volts. In this case the ~ input to amplifier 29 can be biased in the positive direction thereby offsetting the null con-40 dition for 2ero fluid flow to a pre-selected positive value at the out-put 30.
Figure 4 illustrates a cross section of a modified two :
)2B~
element transducer, generally indicated by the numeral lOa, which is the same as the transducer 10 of Figures 1 and 2 but with wire sensing elements 51a and 51b substituted for the film sensing ele-ments lla and llb. Lead wires 52a and 52b are attached to thç
5 sensing wires 51a and 51b, respectively, at each end thereof, by any suitable means, as by iusion welding, capacitance discharge welding or brazing. A larger diameter lead wire can be used in order to reduce the effect of lead wire series resistance upon transducer operation. The same reference numerals as used in 10 Figures 1 and 2 are used to designate the various parts of the trans-ducer lOa which are the same as the transducer 10. It should be realized that the use of wire sensing clemellts can permit a very substantial overall reduction of the transducer size. As long as the support member 15 has sufficient rnechanical integrity to ~upport 15 the transducer array, it can be used to position the two sensing ele-ments 51a and 51b with respect to one another. Because of current-ly available wire sizes, and micro-manufacturing techniques, prac-tical small size transducers can be fabricated which approach the size of a pin head. When such small transducers are to be fabri-20 cated the adhesive and supporting materials which are used can befused quartz or glass.
Figure ;) illustrates a cross section of a modified two element transducer 10~ which is the same as the transducer 10 of ~ :
25 Figures 1 and 2, but with a second support member 53 mounted opposite to the first support member 15. The support members 15 and 53 are connected at one or both ends to the sensing elements lla and llb by suitable attachment means 12b and 12b', respect-ively. As shown, the transducer 10~ can be single-ended, that is, 30 constructed as a c.antilever, or double-endedJ with construction similar to that shown by the transducer 10 of Figure 1. Cantilever : construction is particularly useful when a transducer is desired which senses both speed and sign sense of direction as in pipe line or tunnel applications. For optimum results having symmetrical 35 sensitivity of response for flow from any angle, the support members 15 and 53 should be the same size, and positioned asthe mirror image of each other. :!3iased operation with deflected flow can be realized when the support member 15 is of a different size and spac-ing than support member 53 from sensing elements lla and llb 40 In the case where sensing elements lla and llb are single-ended or cantilever mount ed at one endJ the support member 53 can be ~ an extension of support member 15 which is bent back on itself 180 degrees with sufficient space between the support members to locate sensing elements lla and llb.
;
.
.
.
., '. . ~ .
', " ' :
12 ~
While there have been shown and described the preferred embodiments of the imTention, it is understood that various changes, omissions, and substitutions may be made by those skilled in the art.
INDUSTRIAL APl'LICABILITY
The directional heat loss anemometer transducer of the present invention is adapted for use in various types of commercial apparatus for determining the speed, mass flow, and direction of motion relative to the fluid in which the transducer is immersed.
For e~ample, the transducer of the present invention may be used in long road tunnels to determine the air speed through the tunnel, as well as the direction of air flow.
' ~
" ' :, , l ., ~ .. , ,. - ~ , : . . , ,:
::
Figure 4 illustrates a cross section of a modified two :
)2B~
element transducer, generally indicated by the numeral lOa, which is the same as the transducer 10 of Figures 1 and 2 but with wire sensing elements 51a and 51b substituted for the film sensing ele-ments lla and llb. Lead wires 52a and 52b are attached to thç
5 sensing wires 51a and 51b, respectively, at each end thereof, by any suitable means, as by iusion welding, capacitance discharge welding or brazing. A larger diameter lead wire can be used in order to reduce the effect of lead wire series resistance upon transducer operation. The same reference numerals as used in 10 Figures 1 and 2 are used to designate the various parts of the trans-ducer lOa which are the same as the transducer 10. It should be realized that the use of wire sensing clemellts can permit a very substantial overall reduction of the transducer size. As long as the support member 15 has sufficient rnechanical integrity to ~upport 15 the transducer array, it can be used to position the two sensing ele-ments 51a and 51b with respect to one another. Because of current-ly available wire sizes, and micro-manufacturing techniques, prac-tical small size transducers can be fabricated which approach the size of a pin head. When such small transducers are to be fabri-20 cated the adhesive and supporting materials which are used can befused quartz or glass.
Figure ;) illustrates a cross section of a modified two element transducer 10~ which is the same as the transducer 10 of ~ :
25 Figures 1 and 2, but with a second support member 53 mounted opposite to the first support member 15. The support members 15 and 53 are connected at one or both ends to the sensing elements lla and llb by suitable attachment means 12b and 12b', respect-ively. As shown, the transducer 10~ can be single-ended, that is, 30 constructed as a c.antilever, or double-endedJ with construction similar to that shown by the transducer 10 of Figure 1. Cantilever : construction is particularly useful when a transducer is desired which senses both speed and sign sense of direction as in pipe line or tunnel applications. For optimum results having symmetrical 35 sensitivity of response for flow from any angle, the support members 15 and 53 should be the same size, and positioned asthe mirror image of each other. :!3iased operation with deflected flow can be realized when the support member 15 is of a different size and spac-ing than support member 53 from sensing elements lla and llb 40 In the case where sensing elements lla and llb are single-ended or cantilever mount ed at one endJ the support member 53 can be ~ an extension of support member 15 which is bent back on itself 180 degrees with sufficient space between the support members to locate sensing elements lla and llb.
;
.
.
.
., '. . ~ .
', " ' :
12 ~
While there have been shown and described the preferred embodiments of the imTention, it is understood that various changes, omissions, and substitutions may be made by those skilled in the art.
INDUSTRIAL APl'LICABILITY
The directional heat loss anemometer transducer of the present invention is adapted for use in various types of commercial apparatus for determining the speed, mass flow, and direction of motion relative to the fluid in which the transducer is immersed.
For e~ample, the transducer of the present invention may be used in long road tunnels to determine the air speed through the tunnel, as well as the direction of air flow.
' ~
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::
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A directional heat loss anemometer transducer compris-ing:
(a) at least two similar, thermally and physically separ-ated cylindrical resistive electrical conductors;
(b) each of said conductors having a length at least equal to the largest cross section dimension of the conductor;
(c) a cylindrical support member centrally disposed between and alongside said two resistive electrical conductors;
(d) said cylindrical support member having a straight central portion and a mounting portion on at least one end of said central portion;
(e) said electrical conductors being disposed as a paral-lel pair finitely separated, and mounted parallel to and in close prox-imity to the straight central portion of the cylindrical support member;
(f) said cylindrical support member straight central portion being disposed so that a plane containing the parallel central axes of said two resistive electrical conductors is spaced from the cylindrical support member central portion and is perpendicular to a plane containing the central axis of said cylindrical support member straight central portion and disposed between said two resistive electrical conductors, said cylindrical support and resistive electri-cal conductor axial centers defining an acute angle between center lines through each of said resistive electrical conductors and said cylindrical support when viewed in cross section;
(g) a thermo insulating connective bridging means oper-atively disposed between said two resistive electrical conductors and closing the space between said resistive electrical conductors, there-by preventing connected flow completely around one conductor of said two resistive electrical conductors, independent of the other con-ductor;
(h) said two resistive electrical conductors being sup-ported in the protected lee of the support member straight central portion by attachment means to the support member; and, (i) each of said resistive electrical conductors being provided with electrical connection means, whereby each resistive electrical conductor can be electrically heated by an electrical cur-rent passed through each conductor.
(a) at least two similar, thermally and physically separ-ated cylindrical resistive electrical conductors;
(b) each of said conductors having a length at least equal to the largest cross section dimension of the conductor;
(c) a cylindrical support member centrally disposed between and alongside said two resistive electrical conductors;
(d) said cylindrical support member having a straight central portion and a mounting portion on at least one end of said central portion;
(e) said electrical conductors being disposed as a paral-lel pair finitely separated, and mounted parallel to and in close prox-imity to the straight central portion of the cylindrical support member;
(f) said cylindrical support member straight central portion being disposed so that a plane containing the parallel central axes of said two resistive electrical conductors is spaced from the cylindrical support member central portion and is perpendicular to a plane containing the central axis of said cylindrical support member straight central portion and disposed between said two resistive electrical conductors, said cylindrical support and resistive electri-cal conductor axial centers defining an acute angle between center lines through each of said resistive electrical conductors and said cylindrical support when viewed in cross section;
(g) a thermo insulating connective bridging means oper-atively disposed between said two resistive electrical conductors and closing the space between said resistive electrical conductors, there-by preventing connected flow completely around one conductor of said two resistive electrical conductors, independent of the other con-ductor;
(h) said two resistive electrical conductors being sup-ported in the protected lee of the support member straight central portion by attachment means to the support member; and, (i) each of said resistive electrical conductors being provided with electrical connection means, whereby each resistive electrical conductor can be electrically heated by an electrical cur-rent passed through each conductor.
2. A directional heat loss anemometer transducer as defined in claim 1, wherein:
(a) said two resistive electrical conductors are wires which are solid in cross section.
(a) said two resistive electrical conductors are wires which are solid in cross section.
3. A directional heat loss anemometer transducer as defin-ed in claim 1, wherein:
(a) each of said resistive electrical conductors includes a hollow tubular electrically non-conductive refractory cylindrical substrate supporting body extending the length of the conductor, and a conductive resistance film having a non-zero temperature coefficient of resistance adhered to the outer surface of the substrate body and extending over the length of the substrate body, and an overall pro-tective coating which continuously extends over the outer surface of the conductive resistance film over the entire length of the conductive resistance film.
(a) each of said resistive electrical conductors includes a hollow tubular electrically non-conductive refractory cylindrical substrate supporting body extending the length of the conductor, and a conductive resistance film having a non-zero temperature coefficient of resistance adhered to the outer surface of the substrate body and extending over the length of the substrate body, and an overall pro-tective coating which continuously extends over the outer surface of the conductive resistance film over the entire length of the conductive resistance film.
4. A directional heat loss anemometer transducer as defin-ed in any one of claims 1 through 3, wherein:
(a) said centrally disposed cylindrical support member is a straight cylindrical bar.
(a) said centrally disposed cylindrical support member is a straight cylindrical bar.
5. A directional heat loss anemometer transducer as defin-ed in any one of claims 1 through 3, wherein:
(a) said centrally disposed cylindrical support member is U-shaped with a mounting portion at each end being perpendicular to the central portion.
(a) said centrally disposed cylindrical support member is U-shaped with a mounting portion at each end being perpendicular to the central portion.
6. A directional heat loss anemometer transducer as defin-ed by any one of claims 1 through 3, wherein:
(a) a second cylindrical support member is centrally disposed between and alongside said two cylindrical resistive electri-cal conductors and is situated on the side of said two cylindrical resistive electrical conductors opposite and parallel to said first cylindrical support member.
(a) a second cylindrical support member is centrally disposed between and alongside said two cylindrical resistive electri-cal conductors and is situated on the side of said two cylindrical resistive electrical conductors opposite and parallel to said first cylindrical support member.
7. A directional heat loss anemometer transducer as defin-ed in any one of claims 1 through 3, wherein:
(a) said two cylindrical resistive electrical conductors are connected together in a series arrangement, and a pair of series-connected balancing resistors are connected in parallel across said series connected two cylindrical resistive electrical conductors so as to form a first four arm Wheatstone bridge;
(b) said first four arm Wheatstone bridge being connect-ed in series with a resistor, and with a pair of series balancing resis-tors which are connected in parallel across said first four arm Wheat-stone bridge and said series connected resistor so as to form a second Wheatstone bridge;
(c) said second Wheatstone bridge being operatively con-nected to a first differential error amplifier and current booster amp-lifier whose output is fed back, in a negative feedback manner, to the top of said second Wheatstone bridge, the top of said second Wheat-stone bridge being defined as the junction point of said pair of series balancing resistors with said series resistor which is connected to said first four arm Wheatstone bridge and the bottom of said second Wheatstone bridge being defined as the junction point of the opposite end of said series balancing resistors with the other end of said first four arm Wheatstone bridge, thereby providing for bridge excitation and consequent operation of said directional heat loss anemometer transducer as a constant temperature anemometer, wherein the error signal is taken from the junction of the top of said first four arm Wheatstone bridge and said series resistor and from the junction of said series balancing resistors which form said second Wheatstone bridge which is a feedback controlled bridge;
(d) one of said series balancing resistors forming said second Wheatstone bridge, which is opposite said first four arm Wheatstone bridge, having a non-zero temperature coefficient and functioning as an ambient temperature sensor which modifies the balance of said second Wheatstone bridge in accordance with varia-tions in sensed ambient temperature; and, (e) a second balanced differential amplifier means oper-atively connected across said first four arm Wheatstone bridge with said second amplifier's two input signals being derived from the mid-point or junction of said two cylindrical resistive electrical sensing conductors and the mid-point or junction of said pair of series con-nected balancing resistors, wherein said second balanced differential amplifier produces an amplified composite output signal which is a measurement of speed and direction sign sense of the fluid flow past and across said two cylindrical electrical sensing conductors.
(a) said two cylindrical resistive electrical conductors are connected together in a series arrangement, and a pair of series-connected balancing resistors are connected in parallel across said series connected two cylindrical resistive electrical conductors so as to form a first four arm Wheatstone bridge;
(b) said first four arm Wheatstone bridge being connect-ed in series with a resistor, and with a pair of series balancing resis-tors which are connected in parallel across said first four arm Wheat-stone bridge and said series connected resistor so as to form a second Wheatstone bridge;
(c) said second Wheatstone bridge being operatively con-nected to a first differential error amplifier and current booster amp-lifier whose output is fed back, in a negative feedback manner, to the top of said second Wheatstone bridge, the top of said second Wheat-stone bridge being defined as the junction point of said pair of series balancing resistors with said series resistor which is connected to said first four arm Wheatstone bridge and the bottom of said second Wheatstone bridge being defined as the junction point of the opposite end of said series balancing resistors with the other end of said first four arm Wheatstone bridge, thereby providing for bridge excitation and consequent operation of said directional heat loss anemometer transducer as a constant temperature anemometer, wherein the error signal is taken from the junction of the top of said first four arm Wheatstone bridge and said series resistor and from the junction of said series balancing resistors which form said second Wheatstone bridge which is a feedback controlled bridge;
(d) one of said series balancing resistors forming said second Wheatstone bridge, which is opposite said first four arm Wheatstone bridge, having a non-zero temperature coefficient and functioning as an ambient temperature sensor which modifies the balance of said second Wheatstone bridge in accordance with varia-tions in sensed ambient temperature; and, (e) a second balanced differential amplifier means oper-atively connected across said first four arm Wheatstone bridge with said second amplifier's two input signals being derived from the mid-point or junction of said two cylindrical resistive electrical sensing conductors and the mid-point or junction of said pair of series con-nected balancing resistors, wherein said second balanced differential amplifier produces an amplified composite output signal which is a measurement of speed and direction sign sense of the fluid flow past and across said two cylindrical electrical sensing conductors.
8. A directional heat loss anemometer transducer compris-ing:
(a) two parallel, cylindrical resistive electrical con-ductors which are connected together in a series arrangement, and a pair of series connected balancing resistors which are connected in parallel across said series connected two cylindrical resistive electri-cal conductors so as to form a first four arm Wheatstone bridge;
(b) a thermo insulating connective bridging means oper-atively disposed between said two parallel, cylindrical resistive electrical conductors and closing the space between said parallel, cylindrical resistive electrical conductors, thereby preventing connect-ed flow completely around one conductor of said two parallel, cylin-drical resistive electrical conductors, independent of the other con-duct or;
(c) a cylindrical support member centrally disposed between and alongside said two parallel, cylindrical resistive electri-cal conductors and attached to said conductors by attachment means;
(d) said first four arm Wheatstone bridge being connect-ed in series with a resistor, and with a pair of series balancing resis-tors which are connected in parallel across said first four arm Wheat-stone bridge and said series connected resistor so as to form a second Wheatstone bridge;
(e) said second Wheatstone bridge being operatively con-nected to a first differential amplifier error amplifier and current booster amplifier whose output is fed back, in a negative feedback manner, to the top of said second Wheatstone bridge, and wherein the top of said second Wheatstone is defined as the junction point of said pair of series balancing resistors with said series resistor which is connected to said first four arm Wheatstone bridge and the bottom of said second Wheatstone bridge is defined as the junction point of the opposite end of said series balancing resistors with the other end of said first four arm Wheatstone bridge, thereby providing for bridge excitation and consequent operation of said two cylindrical resistive electrical conductors as a constant temperature anemometer, where-in the error signal is taken from the junction of the top of said first four arm Wheatstone bridge and said series resistor and from the junction of said series balancing resistors which form said second Wheatstone bridge which is a feedback controlled bridge;
(f) one of said series balancing resistors forming said second Wheatstone bridge, which is opposite said first four arm Wheatstone bridge, having a non-zero temperature coefficient and functioning as an ambient temperature sensor which modifies the balance of said second Wheatstone bridge in accordance with varia-tions in sensed ambient temperature; and, (g) a second balanced differential amplifier means oper-atively connected across said first four arm Wheatstone bridge with said second amplifier's two input signals being derived from the mid-point or junction of said two parallel cylindrical resistive electrical conductors and the mid-point or junction of said pair of series con-nected balancing resistors, wherein said second balanced differen-tial amplifier produces an amplified composite output signal which is a measurement of speed and direction sign sense of the fluid flow past and over and across said two parallel cylindrical resistive electrical conductors.
(a) two parallel, cylindrical resistive electrical con-ductors which are connected together in a series arrangement, and a pair of series connected balancing resistors which are connected in parallel across said series connected two cylindrical resistive electri-cal conductors so as to form a first four arm Wheatstone bridge;
(b) a thermo insulating connective bridging means oper-atively disposed between said two parallel, cylindrical resistive electrical conductors and closing the space between said parallel, cylindrical resistive electrical conductors, thereby preventing connect-ed flow completely around one conductor of said two parallel, cylin-drical resistive electrical conductors, independent of the other con-duct or;
(c) a cylindrical support member centrally disposed between and alongside said two parallel, cylindrical resistive electri-cal conductors and attached to said conductors by attachment means;
(d) said first four arm Wheatstone bridge being connect-ed in series with a resistor, and with a pair of series balancing resis-tors which are connected in parallel across said first four arm Wheat-stone bridge and said series connected resistor so as to form a second Wheatstone bridge;
(e) said second Wheatstone bridge being operatively con-nected to a first differential amplifier error amplifier and current booster amplifier whose output is fed back, in a negative feedback manner, to the top of said second Wheatstone bridge, and wherein the top of said second Wheatstone is defined as the junction point of said pair of series balancing resistors with said series resistor which is connected to said first four arm Wheatstone bridge and the bottom of said second Wheatstone bridge is defined as the junction point of the opposite end of said series balancing resistors with the other end of said first four arm Wheatstone bridge, thereby providing for bridge excitation and consequent operation of said two cylindrical resistive electrical conductors as a constant temperature anemometer, where-in the error signal is taken from the junction of the top of said first four arm Wheatstone bridge and said series resistor and from the junction of said series balancing resistors which form said second Wheatstone bridge which is a feedback controlled bridge;
(f) one of said series balancing resistors forming said second Wheatstone bridge, which is opposite said first four arm Wheatstone bridge, having a non-zero temperature coefficient and functioning as an ambient temperature sensor which modifies the balance of said second Wheatstone bridge in accordance with varia-tions in sensed ambient temperature; and, (g) a second balanced differential amplifier means oper-atively connected across said first four arm Wheatstone bridge with said second amplifier's two input signals being derived from the mid-point or junction of said two parallel cylindrical resistive electrical conductors and the mid-point or junction of said pair of series con-nected balancing resistors, wherein said second balanced differen-tial amplifier produces an amplified composite output signal which is a measurement of speed and direction sign sense of the fluid flow past and over and across said two parallel cylindrical resistive electrical conductors.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/110,841 US4279147A (en) | 1980-01-10 | 1980-01-10 | Directional heat loss anemometer transducer |
| US110,841 | 1987-10-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1120286A true CA1120286A (en) | 1982-03-23 |
Family
ID=22335218
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000352271A Expired CA1120286A (en) | 1980-01-10 | 1980-05-20 | Directional heat loss anemometer transducer |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4279147A (en) |
| BE (1) | BE887032A (en) |
| CA (1) | CA1120286A (en) |
| CH (1) | CH638618A5 (en) |
| DE (1) | DE3100428A1 (en) |
| FR (1) | FR2473725A1 (en) |
| GB (1) | GB2067293B (en) |
| NO (1) | NO155218C (en) |
| SE (1) | SE441043B (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4494406A (en) * | 1982-12-23 | 1985-01-22 | Ebtron, Inc. | Means for measuring large area mass flow |
| US4561303A (en) * | 1984-12-06 | 1985-12-31 | Ford Motor Company | Mass airflow sensor with backflow detection |
| US4637251A (en) * | 1986-02-18 | 1987-01-20 | Allied Corporation | Symmetrical bridge circuit for measuring mass air flow |
| US4794795A (en) * | 1986-05-23 | 1989-01-03 | Djorup Robert Sonny | Directional thermal anemometer transducer |
| US4794794A (en) * | 1986-10-30 | 1989-01-03 | Djorup Robert Sonny | Thermal anemometer |
| US4787251A (en) * | 1987-07-15 | 1988-11-29 | Tsi Incorporated | Directional low differential pressure transducer |
| DE3732856A1 (en) * | 1987-09-29 | 1989-04-06 | Siemens Ag | Intelligent air quantity meter |
| US5069066A (en) * | 1990-05-10 | 1991-12-03 | Djorup Robert Sonny | Constant temperature anemometer |
| US5218865A (en) * | 1990-08-16 | 1993-06-15 | Djorup Robert Sonny | Thermal anemometer transducer wind set |
| US5094105A (en) * | 1990-08-20 | 1992-03-10 | General Motors Corporation | Optimized convection based mass airflow sensor |
| CH683800A5 (en) * | 1990-11-13 | 1994-05-13 | Cossonay Meteorology Systems S | An apparatus for measuring physical properties of fluids. |
| US5631417A (en) * | 1995-09-06 | 1997-05-20 | General Motors Corporation | Mass air flow sensor structure with bi-directional airflow incident on a sensing device at an angle |
| US6658941B1 (en) | 1997-07-21 | 2003-12-09 | Helix Technology Corporation | Apparatus and methods for heat loss pressure measurement |
| US6938493B2 (en) * | 1997-07-21 | 2005-09-06 | Helix Technology Corporation | Apparatus and methods for heat loss pressure measurement |
| US5827960A (en) * | 1997-08-28 | 1998-10-27 | General Motors Corporation | Bi-directional mass air flow sensor having mutually-heated sensor elements |
| US6223593B1 (en) | 1997-12-31 | 2001-05-01 | Honeywell International Inc. | Self-oscillating fluid sensor |
| US6019505A (en) * | 1997-12-31 | 2000-02-01 | Honeywell Inc. | Time lag approach for measuring thermal conductivity and specific heat |
| US6169965B1 (en) | 1997-12-31 | 2001-01-02 | Honeywell International Inc. | Fluid property and flow sensing via a common frequency generator and FFT |
| US6234016B1 (en) | 1997-12-31 | 2001-05-22 | Honeywell International Inc. | Time lag approach for measuring fluid velocity |
| US6079253A (en) * | 1997-12-31 | 2000-06-27 | Honeywell Inc. | Method and apparatus for measuring selected properties of a fluid of interest using a single heater element |
| US6502459B1 (en) | 2000-09-01 | 2003-01-07 | Honeywell International Inc. | Microsensor for measuring velocity and angular direction of an incoming air stream |
| US7249516B2 (en) * | 2004-07-28 | 2007-07-31 | Brooks Automation, Inc. | Method of operating a resistive heat-loss pressure sensor |
| US20060021444A1 (en) * | 2004-07-28 | 2006-02-02 | Helix Technology Corporation | Method of operating a resistive heat-loss pressure sensor |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2981104A (en) * | 1954-06-24 | 1961-04-25 | Diana J Anger | Flow measuring system |
| DE1223166B (en) * | 1962-04-12 | 1966-08-18 | Daimler Benz Ag | Measuring device for determining the direction of flowing media |
| US3604261A (en) * | 1969-06-16 | 1971-09-14 | Thermo Systems Inc | Multidirectional thermal anemometer sensor |
| US3900819A (en) * | 1973-02-07 | 1975-08-19 | Environmental Instruments | Thermal directional fluid flow transducer |
| US3991624A (en) * | 1974-06-06 | 1976-11-16 | Leslie Llewellyn Rhys Davies | Wind velocity servo system |
| US4024761A (en) * | 1976-06-11 | 1977-05-24 | Kyma Corporation | Directional hot film anemometer transducer |
| US4206638A (en) * | 1978-12-06 | 1980-06-10 | Djorup Robert Sonny | Directional heat loss anemometer transducer |
-
1980
- 1980-01-10 US US06/110,841 patent/US4279147A/en not_active Expired - Lifetime
- 1980-05-20 CA CA000352271A patent/CA1120286A/en not_active Expired
- 1980-12-17 CH CH931280A patent/CH638618A5/en not_active IP Right Cessation
- 1980-12-23 GB GB8041143A patent/GB2067293B/en not_active Expired
- 1980-12-29 NO NO803952A patent/NO155218C/en unknown
-
1981
- 1981-01-05 FR FR8100043A patent/FR2473725A1/en active Granted
- 1981-01-07 SE SE8100040A patent/SE441043B/en not_active IP Right Cessation
- 1981-01-09 DE DE19813100428 patent/DE3100428A1/en active Granted
- 1981-01-09 BE BE0/203453A patent/BE887032A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2473725B1 (en) | 1985-02-22 |
| SE441043B (en) | 1985-09-02 |
| NO155218C (en) | 1987-03-04 |
| US4279147A (en) | 1981-07-21 |
| DE3100428A1 (en) | 1981-12-03 |
| GB2067293A (en) | 1981-07-22 |
| DE3100428C2 (en) | 1987-10-15 |
| NO803952L (en) | 1981-07-13 |
| GB2067293B (en) | 1983-11-30 |
| FR2473725A1 (en) | 1981-07-17 |
| SE8100040L (en) | 1981-07-11 |
| CH638618A5 (en) | 1983-09-30 |
| NO155218B (en) | 1986-11-17 |
| BE887032A (en) | 1981-05-04 |
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