USOO674881 3B1

(12) United States Patent (10) Patent No.: US 6,748,813 B1

Barger et al. (45) Date of Patent: Jun. 15, 2004

(54) CORIOLIS MASS FLOW CONTROLLER OTHER PUBLICATIONS

(75) Inventors: Michael J. Barger, Souderton, PA Search Report dated Jan. 13, 2003 from the Australian
(US); Joseph C. Dille, Telford, PA Patent Office for Patent Application Ser. No. 200105073–1,
(US); Timothy W. Scott, Lansdale, PA filed Aug. 17, 2001.
(US); Jeffrey L. Whiteley, Quakertown, Novel Resonant Micromachined Silicon Devices for Fluid
PA (US) Applications (Densitometer, Coriolis Mass Flow Sensor and
Diffuser Pump), by Peter Enoksson, submitted to the School
(73) Assignee: Emerson Electric Company, St. Louis, of Electrical Engineering, Royal Institute of Technology, in
MO (US) partial fulfilment of the requirements for the degree of
Doctor of Philosophy.
(*) Notice: Subject to any disclaimer, the term of this Written opinion dated Apr. 2, 2003 from Australian Patent
patent is extended or adjusted under 35 Office for Singapore Patent Application No.
U.S.C. 154(b) by 0 days. SG2OO 105073-1.
(21) Appl. No.: 09/641,698 Primary Examiner Edward Lefkowitz
(22) Filed: Aug. 18, 2000 Assistant Examiner Lilybett Martir
(74) Attorney, Agent, or Firm-Howrey Simon Arnold &
Related U.S. Application Data White LLP

(63) Continuation-in-part of application No. 09/430,881, filed on (57) ABSTRACT

Nov. 1, 1999, which is a continuation-in-part of application
No. 09/326,949, filed on Jun. 7, 1999. A Coriolis mass flow Sensor includes a flow tube, a light
(60) Provisional application No. 60/111,504, filed on Dec. 8, Source positioned adjacent a first Side of the flow tube and
1998. a light detector positioned adjacent a Second Side of the flow
(51) Int. Cl. .................................................. G01F1/84 tube. A drive device is operatively situated relative to the
(52) U.S. Cl. .............................. 73/861.355; 73/861.354 flow tube for vibrating the flow tube, such that the flow tube
moves through a path defined between the light Source and
(58) Field of Search ....................... 73/861.355,861.38, the light detector. In other aspects of the invention, a Coriolis
73/861.356, 861.354 mass flow Sensor includes a flow tube and a frame having the
(56) References Cited flow tube mounted thereon. A drive device is operatively
U.S. PATENT DOCUMENTS
situated relative to the frame for vibrating the frame and at
least one pick off sensor is situated relative to the flow tube
4,109,524 A 8/1978 Smith ....................... 73/194 B So as to measure the twist in the flow tube due to Coriolis
4,127.028 A 11/1978 Cox et al. ................. 73/194 B force. Other aspects of the invention concern a Straight-tube
4.252,028 A 2/1981 Smith et al. ............. 73/861.38 Coriolis mass flow sensor. A flexible flow tube defines a
4,311,054 A 1/1982 Cox et al. .............. 73/861.356 generally linear flow path. A drive device is positioned to
RE31,450 E * 11/1983 Smith ...................... 73/861.38 actuate the flow tube, and first and Second pick off Sensors
(List continued on next page.) are positioned at the first and Second ends of the flow tube,
FOREIGN PATENT DOCUMENTS respectively. The first and Second pick off Sensors output a
Signal in response to movement of the flow tube, wherein a
DE 42 26 391 A1 8/1992 ............. GO1F/1/84 Coriolis force established by a flow of material through the
DE 196 OS 923 8/1997 flow tube causes a phase shift between the Signals output by
EP O 275 367 A2 10/1987 ............. GO1F/1/84 the first and Second pick off Sensors.
GB 2 221 3O2 1/1990
(List continued on next page.) 23 Claims, 24 Drawing Sheets

l
 US 6,748,813 B1
Page 2

U.S. PATENT DOCUMENTS 5,301,557 A 4/1994 Cage et al. .............. 73/861.38

5,321,991 A 6/1994 Kalotay ................... 73/861.37
4,422,338 A 12/1983 Smith ...................... 73/861.38 5,322,399 A 6/1994 Felbush ...................... 409/131
4,444,059 A 4/1984 Smith .............. ... 73/861.37 5,331,859 A 7/1994 Zolock ............. . 73/861.38
4,449.893 A 5/1984 Beckman et al. ........... 417/322 5,344,717 A 9/1994 Dutton, Jr. et al. ......... 428/598
4,491,009 A 1/1985 Ruesch ....................... 73/32 A 5,347.874 A 9/1994 Kalotay et al. .......... 73/861.38
4,491,025 A 1/1985 Smith et al. ... 73/861.38 5,349,872 A 9/1994 Kalotay et al. .......... 73/861.38
4,559,833 A * 12/1985 Sipin ............ 73/861.355 5,357,811 A 10/1994 Hoang ........... . 73/861.38
4,633,121 A * 12/1986 Ogawa et al. .............. 3.10/331 5,359.881. A 11/1994 Kalotay et al. ............ 73/54.06
4,726,508 A 2/1988 Carpenter .. 228/263.13 5,370.002 A 12/1994 Normen et al. .......... 73/861.37
4,738,143 A 4/1988 Cage et al. 73/861.38 5,379,649 A 1/1995 Kalotay ......... . 73/861.38
4,738,144 A 4/1988 Cage ...... 73/861.38 5,400,653 A 3/1995 Kalotay ...... 73/861.37
4,747,312 A 5/1988 Herzl ..... 73/861.38 5.448.921 A 9/1995 Cage et al. . . 73/861.38
4,756,198 A 7/1988 Levien ......... ... 73/861.38 5,469,748 A 11/1995 Kalotay ...... . 73/861.38
4,768,384 A 9/1988 Flecken et al. ... 73/861.02 5,493.918 A 2/1996 Barat et al. .............. 73/862.41
4,768,385 A 9/1988 Cage ............ ... 73/861.38 5,497,666 A 3/1996 Patten et al. ............. 73/861.38
4,777,833. A 10/1988 Carpenter .. ... 73/861.38 5,549,009 A 8/1996 Zaschel ...... ... 73/861.355
4,801,897 A 1/1989 Flecken ...................... 331/155 5,555,190 A 9/1996 Derby et al. ................ 364/510
4,817,448 A 4/1989 Hargarten et al. ... 73/861.38 5,594,180 A 1/1997 Carpenter et al. 73/861.356
4,823,592 A 4/1989 Hahn .............................. 73/3 5,597,949 A 1/1997 Kalotay ............ ... 73/54.01
4,823,613 A 4/1989 Cage et al. ... 73/861.38 5,654,502 A 8/1997 Dutton ............. 73/152.18
4,831,885 A 5/1989 Dahlin ......... ... 73/861.38 5,661232 A 8/1997 Van Cleve et al. ........ 73/54.05
4,843,890 A 7/1989 Samson et al. ... 73/861.38 5,679.906 A 10/1997 Van Cleve et al. ..... 73/861.353
4,845,989 A 7/1989 Titlow et al. . ... 73/597 5,687,100 A 11/1997 Buttler et al................ 364/558
4,872,351 A 10/1989 Ruesch ...... 73/861.04 5,705,754 A 1/1998 Keita et al. ............ 73/861.357
4,876,879 A 10/1989 Ruesch ....................... 73/32 A 5,728,952 A 3/1998 Yao et al. .............. 73/861.357
4,876,898 A 10/1989 Cage et al. ... 73/861.38 5,734,112 A 3/1998 Bose et al. . ... 73/861.56
4,879,911. A 11/1989 Zolock ... ... 73/861.38 5,753,827 A 5/1998 Cage ............. ... 73/861.356
4,895,031 A 1/1990 Cage ......... ... 73/861.38 5,773,727 A 6/1998 Kishiro et al. ......... 73/861.355
4,899,588 A 2/1990 Titlow et al. .... 73/597 5,796,010 A * 8/1998 Kishiro et al. . 73/861.357
4,911,006 A 3/1990 Hargarten et al. ... 73/198 5,796,011 A 8/1998 Keita et al. ............ 73/861.357
4,934,196 A 6/1990 Romano ....... ... 73/861.38 5,804,740 A 9/1998 Kalinoski et al. ........ 73/861.24
4949,583 A 8/1990 Lang et al. ... 73/861.37 5,854,430 A 12/1998 Drahm et al. ..... ... 73/861.357
4,955,239 A 9/1990 Cage et al. ... 73/861.38 6,164,140 A 12/2000 Kalinoski .............. 73/861.357
4,996.871 A 3/1991 Romano ..................... 73/32 A
5,009,109 A 4/1991 Kalotay et al. .......... 73/861.38 FOREIGN PATENT DOCUMENTS
5,020,380 A 6/1991 Keita ... 73/861.37 WO 92 14123 8/1992
5,027,662 A 7/1991 Titlow et al. ............ 73/861.38
5,157.975 A 10/1992 Tanaka et al. ........... 73,863s WO
WO
WO9409344
96 2.1159
4/1994
7/1996
5,228,327 A 7/1993 Bruck ............................. 73/3
5,231,884.
24-----
A 8/1993 Zolock .................... 7386 13s Y
WO
WO97/26508
WOOO34748
7/1997
6/2000
5,233,312 A 8/1993 Duft et al. .................. 330/259
5,295,084 A 3/1994 Arunachalam et al. ..... 364/558 * cited by examiner
U.S. Patent Jun. 15, 2004 Sheet 1 of 24 US 6,748,813 B1
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U.S. Patent Jun. 15, 2004 Sheet 24 of 24 US 6,748,813 B1

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 US 6,748,813 B1
1 2
COROLIS MASS FLOW CONTROLLER example, the magnet is mounted on the tube and the coil is
mounted on the Stationary package wall. The coil will move
CROSS-REFERENCE TO RELATED through the magnet's field, inducing a current in the coil.
APPLICATIONS This current is proportional to the Velocity of the magnet
This Application is a continuation-in-part of U.S. patent relative to the coil. Since this is a Velocity measurement, the
Velocity, and thus the Signal, is at the maximum when the
application Ser. No. 09/430,881 filed Nov. 1, 1999, which is flow tube crosses its rest point (Zero crossing). The Coriolis
a continuation-in-part of U.S. patent application Ser. No. force induced twist causes a phase shift in the Velocity Signal
09/326,949 filed Jun. 7, 1999, which claims the benefit of that is detected by measuring the difference in the Zero
U.S. Provisional Patent Application Serial No. 60/111,504, crossing times between the two Velocity Sensors. In practice
filed Dec. 8, 1998. this places a large accuracy burden on the time measurement
BACKGROUND OF THE INVENTION circuitry. This may limit the ultimate sensitivity of mass flow
measurement by this technique.
1. Field of the Invention Further, the flow rate capabilities of known devices based
The invention relates generally to a mass flow measure 15 on Coriolis technology often are limited to flow rates that are
ment and control, and more particularly, to a mass flow higher than desired for many applications. Moreover, exist
measurement and control device based on the Coriolis force ing Coriolis mass flow measuring devices only provide for
effect and having an integrated flow control valve with mass flow Sensing with no integral flow control capabilities.
asSociated Sense, control and communication electronics. It has been left to the user to provide any means for
2. Description of Related Art controlling flow.
Mass flow measurement based on the Coriolis force effect
The present invention addresses shortcomings associated
with the prior art.
is achieved in the following manner. The Coriolis force SUMMARY OF THE INVENTION
results in the effect of a mass moving in an established
direction and then being forced to change direction with a 25 In one aspect of the present invention, a Coriolis mass
vector component normal to the established direction of flow Sensor includes a flow tube, a light Source positioned
flow. This can be expressed by the following equation: adjacent a first Side of the flow tube, a light detector
positioned adjacent a Second Side of the flow tube, and a
F=2Mx (1) drive device operatively situated relative to the flow tube for
vibrating the flow tube, such that the flow tube moves
-e
Where F (the Coriolis force vector) is the result of the through a path defined between the light Source and the light
detector. In certain embodiments, the light Source emits
croSS product of M (the momentum vector of the flowing infrared light, Such as an infrared LED used in conjunction
mass) and o (the angular Velocity vector of the rotating with an infrared photo diode.
coordinate System). 35 In accordance with other aspects of the invention, a
In a rotating System, the angular Velocity vector is aligned flexible-tube Coriolis mass flow sensor includes a flexible
along the axis of rotation. Using the “Right Hand Rule”, the flow tube having first and second ends. The flow tube defines
fingerS define the direction of rotation and the thumb, a generally linear flow path, and a drive device is positioned
extended, defines the angular velocity vector direction. In to actuate the flow tube. First and Second pick off Sensors are
the case of the typical Coriolis force flow Sensor, a tube, 40 positioned at the first and second ends of the flow tube,
through which fluid flow is to be established, is vibrated. respectively. The first and Second pick off Sensors each
Often the tube is in the shape of one or more loops. The loop output a signal in response to movement of the flow tube,
shape is Such that the mass flow vector is directed in wherein a Coriolis force established by a flow of material
opposite directions at different parts of the loop. The tube through the flow tube causes a phase shift between the
loops may, for example, be “U” shaped, rectangular, trian 45 Signals output by the first and Second pick off Sensors.
gular or “delta” shaped or coiled. In the Special case of a In another aspect of the invention, a Coriolis mass flow
Straight tube, there are two Simultaneous angular Velocity Sensor includes a flow tube, a frame having the flow tube
vectors that are coincident to the anchor points of the tube mounted thereon, a drive device operatively situated relative
while the mass flow vector is in a Single direction. to the frame for Vibrating the frame, and at least one pick off
The angular velocity vector changes directions Since, in a 50 Sensor Situated relative to the flow tube So as to measure the
Vibrating System, the direction of rotation changes. The twist in the flow tube due to Coriolis force. The frame, for
result is that, at any given time, the Coriolis force is acting example, may comprise a Silicon frame to which a stainless
in opposite directions where the mass flow vectors or the Steel flow Sensor tube is attached.
angular Velocity vectors are directed in opposite directions. BRIEF DESCRIPTION OF THE DRAWINGS
Since the angular Velocity vector is constantly changing due 55
to the vibrating System, the Coriolis force is also constantly Other objects and advantages of the invention will
changing. The result is a dynamic twisting motion being become apparent upon reading the following detailed
imposed on top of the oscillating motion of the tube. The description and upon reference to the drawings in which:
magnitude of twist is proportional to the mass flow for a FIGS. 1A and 1B are block diagrams conceptually illus
given angular Velocity. 60 trating a Coriolis mass flow controller and Sensor in accor
Mass flow measurement is achieved by measuring the dance with aspects of the present invention;
twist in the Sensor tube due to the Coriolis force generated FIGS. 2A and 2B illustrate a Coriolis mass flow sensor
by a fluid moving through the Sensor tube. Typical known employing an electromagnetic drive in accordance with an
devices use pick off Sensors comprising magnet and coil embodiment if the present invention;
pairs located on the flow tube where the Coriolis force's 65 FIGS. 3A and 3B illustrate a Coriolis mass flow sensor
induced displacement is expected to be greatest. The coil employing an electroStatic drive in accordance with an
and magnet are mounted on opposing Structures, for embodiment if the present invention;
 US 6,748,813 B1
3 4
FIGS. 4A and 4B illustrate a Coriolis mass flow sensor flow controller in accordance with an embodiment of the
employing an acoustic drive in accordance with an embodi present invention;
ment if the present invention; FIG. 25 illustrates a hybrid Coriolis mass flow sensing
FIGS. 5A, 5B and 5C illustrate a Coriolis mass flow tube in accordance with an embodiment of the present
Sensor employing a piezoelectric drive in accordance with invention;
an embodiment if the present invention; FIGS. 26A and 26B illustrate Wheatstone bridges func
FIG. 6 is a Schematic of a lock-in amplifier for measuring tioning as piezoresistive Sensors for the hybrid tube Structure
the Coriolis force induced phase shift in accordance with the illustrated in FIG. 25;
present invention; FIG. 27 is a block diagram Schematically illustrating a
FIG. 7 is a schematic of a dual channel lock-in amplifier Straight tube flow Sensor in accordance with the present
for measuring the Coriolis force induced phase shift in invention;
accordance with the present invention; FIG. 28 is a block diagram Schematically illustrating an
FIG. 8 is a graph illustrating the relationship between the alternative Straight tube flow Sensor in accordance with the
amplitudes of input signals from Sensor tube position Sen 15 present invention; and
Sors using Signal processing methods in accordance with the FIGS. 29A and 29B schematically illustrate exemplary
present application; piezoelectric tilt actuators in accordance with the present
invention.
FIG. 9 is a schematic of a dual lock-in amplifier for
measuring the Coriolis force induced phase shift in accor While the invention is susceptible to various modifica
dance with the present invention; tions and alternative forms, specific embodiments thereof
FIG. 10 is a schematic of a dual lock-in amplifier includ have been shown by way of example in the drawings and are
ing reference frequency adjustment for measuring the Corio herein described in detail. It should be understood, however,
lis force induced phase shift in accordance with the present that the description herein of Specific embodiments is not
invention; intended to limit the invention to the particular forms
25 disclosed, but on the contrary, the intention is to cover all
FIG. 11 illustrates a first embodiment of a capacitive modifications, equivalents, and alternatives falling within
displacement probe in accordance with the present inven the Spirit and Scope of the invention as defined by the
tion; appended claims.
FIG. 12 illustrates a second embodiment of a capacitive DETAILED DESCRIPTION OF THE
displacement probe in accordance with the present inven INVENTION
tion;
FIG. 13 illustrates a third embodiment of a capacitive Illustrative embodiments of the invention are described
displacement probe in accordance with the present inven below. In the interest of clarity, not all features of an actual
tion; implementation are described in this specification. It will of
FIG. 14 is a perspective view of a Coriolis mass flow 35
course be appreciated that in the development of any Such
controller in accordance with an embodiment of the present actual embodiment, numerous implementation-Specific
invention; decisions must be made to achieve the developers' specific
FIG. 15 is a sectional view of the Coriolis mass flow
goals, Such as compliance with System-related and busineSS
related constraints, which will vary from one implementa
controller shown in FIG. 14, tion to another. Moreover, it will be appreciated that Such a
40
FIG. 16 is an exploded view of the Coriolis mass flow development effort might be complex and time-consuming,
controller shown in FIG. 15; but would nevertheless be a routine undertaking for those of
FIGS. 17A and 17B illustrate aspects of a prior art ordinary skill in the art having the benefit of this disclosure.
threaded valve connection and a Sealed threaded valve FIG. 1A illustrates a Coriolis based mass flow sensor and
connection in accordance with the present invention, respec 45 controller in accordance with embodiments of the present
tively; invention. It is comprised of essentially two Separate opera
FIG. 18 is a perspective view of an embodiment of a tional Systems: a Coriolis Sensor pickup and drive System A,
Coriolis mass flow controller in accordance further aspects and an application and control System B. The Coriolis Sensor
of the present invention; pickup and drive System interfaces with the Coriolis Sensor
FIG. 19 illustrates a Coriolis mass flow device employing 50 1. The application and control System B provides an inter
an optical pick off Sensor in accordance with embodiments face for a user 5, and provides control Signals to a flow
control device Such as a valve 6.
of the present invention;
FIG. 20 is a block diagram illustrating a Coriolis mass The purpose of the Sensor pickup and drive System A is to
control and sense the motion of the Coriolis sensor 1 for the
flow controller employing an optical pick off Sensor as purpose of determining relative mass flow as a function of
shown in FIG. 19: 55
Coriolis force, and relative density as a function of resonant
FIG.21 is a block diagram illustrating portions of a Sensor frequency. The exemplary Sensor pickup and drive System A
pick off and drive circuit in accordance with aspects of the provides three data values to the application and control
present invention; system B:
FIG. 22 is a block diagram illustrating portions of an 60 1. DeltaT the time difference that relates to the phase lag
application and control circuit in accordance with aspects of of one side of the Sensor tube to the other indicating
the present invention; relative mass flow.
FIG. 23 is a block diagram conceptually illustrating 2. Frequency-the resonant frequency of the Sensor tube
portions of a HART interface for a Coriolis mass flow that relates to the relative density of the measured
controller in accordance with the present invention; 65 material.
FIGS. 24A and 24B are front and side sectional views, 3. Temperature-an RTD is measured to determine the
respectively, of the flow Sensing portion of a Coriolis mass temperature of the Sensor tube.
 US 6,748,813 B1
S 6
The application and control system B uses DeltaT in Surface is also accomplished, which may be desirable for
conjunction with calibration constants to present the desired certain deposited materials. Also, chemical reactions at the
mass flow units to the user 5. It also uses Frequency in Surface may be accomplished by accelerating the chemical
conjunction with calibration constants to present the desired Species So that the kinetic energy can be used to activate or
density and/or volumetric flow units to the user 5. Tempera enhance the chemical reaction.
ture is used for compensation of both mass flow and density Tube materials used for the Coriolis flow sensing tube 2
calculations. The application and control System B uses the in particular embodiments of the present invention are
mass or Volume flow unit output in comparison with the Austenitic and Martensitic Stainless Steels, high nickel
user's Set point input to control the valve 6 that regulates alloys, Titanium and Zirconium and their alloys, particularly
flow to the desired Setting. Titanium-Vanadium-Aluminum alloys and Zircalloy (for
FIG. 1B is a block diagram conceptually illustrating a their high yield strength and low Young's modulus), Silicon,
Coriolis mass flow Sensor in accordance with aspects of the Sapphire, Silicon carbide, Silica glass and plastics. Tube
coating materials employed in accordance with the present
present invention. The Coriolis mass flow sensor 1 includes invention include Silicon carbide, nickel, chrome, diamond,
a flow sensor tube 2, with a drive device 3 situated relative the refractory carbides, the refractory metal nitrides, and
thereto So as to vibrate the tube 2. Displacement gauges 4 are 15 refractory metal oxides.
positioned relative to the tube 2 So as to measure the twist In other embodiments, the Sensing tube comprises a
in the tube 2 due to Coriolis force. hybrid of structures of different material compositions
A typical material for the sensor tube 2 is 31.6L stainless mechanically attached So as to utilize the best material
Steel. Reasons for using 31.6L StainleSS Steel include that it properties of each part of the Structure. The Sensor Structure
is resistant to chemical attack from many Substances, it is is divided into a wetted portion and a non-wetted portion, for
resistant to rupture from normal proceSS pressures, it is example. The wetted portion may be a tube of any material
typically noncontaminating and can be readily formed to the compatible with the application fluid, including metallic,
desired shape of a Coriolis sensor tube. However, 31.6L ceramic and Silica tubes. This tube is attached to a vibratory
Stainless Steel is not Suitable for all applications. Therefore, Structure, Such as a frame, that conveys the tube in the proper
it is necessary that other tube materials be available to cover 25 vibrational mode to induce the Coriolis forces. The vibratory
applications not Suitable for 31.6L Stainless Steel. Known structure may itself be a tube in which the wetted tube fits,
devices use Silicon as an alternate material to 316L StainleSS or it may be a frame to which the tube is attached. The
Steel. The advantage of Silicon over 31.6L Stainless Steel is Vibratory Structure may be made of a material that can be
that Sensor tubes can be made in a Smaller form than can be shaped into a beam of a form to Support the wetted tube. An
realized by 316L stainless steel. example would be Silicon etched from a wafer in a shape that
Another consideration for material Selection for the Sensor would Support a wetted tube that could be stainleSS Steel,
tube 2 is the resistance to StreSS induced or enhanced plastic or other material that could be shaped into a tube to
corrosion. StreSS is generated at the base of the bending arm convey flow.
where the tubes are mounted. In polycrystalline materials FIGS. 2A and 2B illustrate a Coriolis mass flow sensor 1
StreSS will cause impurities in the material to diffuse and 35 in accordance with particular embodiments of the present
concentrate at grain boundaries between the microcrystal invention. The Coriolis mass flow sensor 1 employs an
line granular regions. This will, in many cases, weaken the electromagnetic drive 10 that includes an electromagnet 12
bonds between the microcrystalline grains making the mate driven by a signal Source (not shown), which, in the embodi
rial to be more Susceptible to chemical attack. Single crystal ment illustrated, comprises a Sinusoidal signal Source. The
materials like Silicon or Sapphire are less likely to be affected 40 electromagnet 12 is situated near a Small permanent magnet
in this manner. 14 mounted on a sensor tube 16. The sensor tube 16 is
Metals, like 316L Stainless Steel are usually polycrystal connected to a base 18 that includes first and Second ports
line and therefore more Susceptible to this type of chemical 19, so as to define a flow path from one port 19 through the
attack to varying degrees. Amorphous materials like Silica flow tube 16 to the other port 19. The exemplary sensor tube
glass and Several plastics also are more resistant to StreSS 45 16 shown in the embodiments disclosed herein is generally
induced chemical attack, Since they do not have a grain “U” shaped, though other shapes, Such as delta shaped,
Structure like polycrystalline materials. Tube materials that rectangular, coiled, or Straight tubes may also be used.
are Susceptible to chemical attack may have their Surfaces Alternative tube shapes are discussed further herein below.
modified or coated in Such a way to minimize corrosion or Moreover, further embodiments are envisioned that employ
attack at the Surfaces if the use of the underlying material is 50 multiple parallel Sensing tubes, providing redundancy,
otherwise attractive. rangeability (wherein selected tubes may be valved in or
Surface modification may be accomplished by ion out), greater accuracy, etc.
implantation, thermal diffusion, and chemical or electro FIGS. 3A and 3B illustrate an embodiment similar to that
chemical reaction. The intent, here, is to remove, shown in FIG. 2, using an electroStatic drive. The electro
redistribute, or introduce elemental or molecular species that 55 Static drive 20 includes a charge plate 22 positioned near a
leave a chemically resistant layer at the Surface. Surface small dielectric plate 24 mounted on the sensor tube 16. If
coating may be accomplished by thermally activated depo the tube 16 is made of dielectric material, then the charge
Sition from a vapor, liquid or powder impinging on the plate 22 is positioned near the tube 16 and the dielectric plate
Surface at elevated temperatures. Lower temperatures may 24 may be eliminated. Again, the charge plate is driven by
be used if the chemically reactive Species is also excited or 60 a signal Source (not shown), Such as a sinusoidal signal
ionized by plasma or an intense photon flux as from a laser. Source. A Voltage applied to the charge plate 22 will produce
Other materials resistant to chemical attack may be depos an electric field between it and the dielectric plate 24. This
ited by nonreactive, physical vapor deposition as accom will produce a Surface charge on the dielectric plate 24. AS
plished by thermal or electron beam evaporation or by ion the Voltage polarity is rapidly changed on the charge plate
Sputtering. If Sputtering is accomplished using a highly 65 22, the resultant electric field between it and the dielectric
energetic ion beam So that the Sputtered species is chemi plate 24 will alternately be attractive or repulsive causing the
cally excited or ionized, then a chemical reaction with the flow tube 16 to vibrate.
 US 6,748,813 B1
7 8
FIGS. 4A and 4B illustrate another embodiment of the A first Signal processing technique uses a lock-in amplifier
Coriolis mass flow Sensor 1 that employs a novel acoustic with a reference Signal Supplied by one of the displacement
drive 30. The acoustic drive 30 includes a small speaker 32 gauges 50, and an input signal Supplied by the other dis
placed near the tube 16. The preSSure waves generated by the placement gauge 50. The lock-in amplifier may be imple
speaker 32 cause the tube 16 to vibrate. mented by hardware or software, or a combination of both.
In FIGS.5A, 5B and 5C, yet another embodiment of the Either gauge 50 may Supply the reference or the input signal.
Coriolis mass flow sensor 1 is illustrated. The Coriolis mass
flow sensor 1 of FIGS. 5A, 5B and 5C uses a piezoelectric The phase output from the lock-in amplifier is proportional
drive 40, wherein two piezoelectric stacks 42 are positioned to flow. FIG. 6 is a functional Schematic of a lock-in
on opposite Sides each leg of the flow tube 16, in effect amplifier 52, with which such a method for measuring the
creating two bimorphs on each leg 16 as shown in FIG. 5. Coriolis force induced phase shift in accordance with the
The piezoelectric and reverse piezoelectric effects would be present invention may be implemented. The Signals are
used to either drive and/or sense the deflection of the tube moving left to right as illustrated in FIG. 6. The Left input
16. 100 and Right input 102 signals are from the Left and Right
Mass flow measurement is achieved by measuring the 15 displacement gauges 50 respectively. For example, the Left
twist in the Sensor tube due to the Coriolis force generated input 100 may be used as the reference signal. The sine out
by a fluid moving through the Sensor tube. For example, in 103 is the drive signal, phase locked to the Left input 100
known Coriolis mass flow Sensors, pick off Sensors com signal. This will drive the flow sensor tube 16 at resonance.
prising magnet and coil pairs are typically located on the
flow tube where the Coriolis forces induced displacement is The Right Input 102 signal is mixed with the Left/Reference
expected to be greatest. The coil and magnet are mounted on Input 100 signal and its 90° phased-shifted signal 104 in the
opposing Structures, for example, the magnet is mounted on two Phase Sensitive Detectors (PSDs) 106. Functionally, the
the tube and the coil is mounted on the Stationary package PSDs 106 multiply the two signals, producing a high fre
wall. The coil will move in and out of the magnet’s field, quency component and a DC component. The low pass
inducing a current in the coil. This current is proportional to 25 filters 108 remove the high frequency component producing
the velocity of the magnet relative to the coil. Since this is a DC voltage at the X and Youtputs 110, 112. The X output
a Velocity measurement, the Velocity, and thus the Signal, is 110 is called the “in-phase” component and the Youtput 112
at the maximum when the flow tube crosses its rest point is called the “quadrature' component of the vector Signal
(Zero crossing). The Coriolis force induced twist causes a relative to the reference Signal. Each of these components is
phase shift in the Velocity signal that is detected by mea
Suring the difference in the Zero crossing times between the phase Sensitive; however, the vector magnitude and phase
two Velocity Sensors. In practice this places a large accuracy components can be separated by the following relationships:
burden on the time measurement circuitry. This may limit
the ultimate sensitivity of mass flow measurement by this R-VxxY, the magnitude Eq. I
technique. 35
U.S. Pat. No. 5,555,190, assigned to the assignee of the 0=tan"(Y|X), the phase angle. Eq. 2
present application, discloses digital Signal processing meth
ods and devices for determining frequency and phase rela The relationship between the outputs from the lock-in
tionships of a vibrating Sensor tube Such as the tubes amplifier 52 and the inputs from the displacement gauges 50
disclosed in conjunction with the Coriolis mass flow Sensing 40 is derived as follows:
devices disclosed herein. The entire specification of U.S. Consider the two Signals as Sine waves with arbitrary
Pat. No. 5,555,190 is incorporated by reference herein. amplitudes and arbitrary phase difference. Each Signal can
Aspects of the present invention provide a flow measure be represented as below:
ment technique that provides for a lower flow capability, is
more direct and requires leSS accuracy in the circuitry than 45
typical time based signal conditioning techniques. Referring
to the embodiments illustrated in FIGS. 2-4, displacement V =B sin(otxp)
of the vibrating Sensor tube is measured using capacitive
pick off Sensors. Two capacitance displacement gauges 50
are positioned near the tube 16 at positions Symmetric to the 50 At the bottom PSD 106 the following operation occurs:
shape of the tube 16 So as to measure the twist in the Sensor
tube 16 due to the Coriolis force generated by a fluid moving X'=V, (V,h)=A sincot B sin(otxp)
through the sensor tube 16. In specific embodiments of the 1
present invention, the capacitance displacement gauges 50 X = 5AB|cos) - cos(2cot + i)
are miniaturized and Surface mounted on the Sensor package 55
wall or on a sensor block inserted inside the loop of the flow
sensor tube. The twist in the sensor tube 16 due to the This signal has a DC voltage component and an AC
Coriolis force results in a phase shift between the two signals component at twice the frequency. The Low Pass Filter
from the capacitance displacement gauges 50. Since this is (LPF) 108 removes the AC component leaving
a displacement measurement, the Signal is directly propor 60
tional to the displacement. The relative displacement of each 1
Side of the tube is measured as a phase shift. The gauge X = 5ABcost).
driver and Signal conditioning electronicS translate the rela
tive displacement of the tube 16 into a high level Signal
which is a function of the phase shift that can be used to 65 At the top PSD 106 the following operation occurs:
measure the Coriolis effect when flow is established through
the tube 16. Y'-Acos cot B sin(otxp)
 US 6,748,813 B1
10
We have a cosine multiplier since cos (ot=sin(cotx90). This signal has a DC voltage component and an AC
component at twice the frequency. The Low Pass Filter
1 1
Y = - 2 ABsini) + 5 ABsin(20t + (5)
(LPF) 108 removes the AC component leaving
5
x =– 5 A - lAB
5 cosis.
Again, we have a Signal with AC and DC components,
which after passing through the LPF 108, results in the
following: At the top PSD 106 the following operation occurs:
1 1O
Y = - 5 ABsin). Y=A cos (otA sin ot-B sin(cotxp)

We have a cosine multiplier since coscot=sin(cotx90).

Calculating the magnitude, R, and the phase angle, 0,
from equations 1 and 2 we have: 15 1 1 1
Y = iA’ sin2iot- 5ABsin) 5 ABsin(20 + (b)
R -= 2 AB
Again, we have a Signal with AC and DC components,
and 2O
which after passing through the LPF, results in the follow
ing:
0=p
1
These calculations may be executed by any Suitable digital Y = - 5ABsin).
or analog processing device 120. The vector phase is pro 25
portional to mass flow. Calculating the magnitude, R, and the phase angle, 0,
Another method in accordance with embodiments of the
invention requires a dual channel lock-in amplifier with the from equations 1 and 2 we have:
reference signal and one input Signal Supplied by one of the
displacement gauges 50 and a Second input Signal Supplied R =- 2 Ava -- B-2abcosti an d 6=ta -( Bcos(j
Bsini- A
by the other displacement gauge 50. The lock-in amplifier
may be implemented by hardware or Software, or a combi
nation of both. The difference between the two input signals cp is no longer the phase angle, but is the arctangent, a
is then measured against the reference Signal. The resultant function of the phase angle and the amplitudes of the Left
phase output from the lock-in amplifier is proportional to 35 and Right input signals. Analysis of this equation shows that
flow. FIG. 7 is a functional Schematic of a dual channel
lock-in amplifier 54. The Signals are moving in the same 0 is a Strong function of (p. In fact, the relative amplitudes of
manner and have the same definitions as in FIG. 6. The Left the input signals can control the Strength of this function.
input 100 is also used as the reference signal. As before, the This can be illustrated in graph shown in FIG. 8, in which
sine out 103 is the drive signal, phase locked to the Left 40
A and B are the amplitudes of the Left and Right signals
input 100 signal. In this case, the Left Input 100 signal is respectively. AS the amplitudes are more closely matched,
subtracted from the Right Input 102 signal and mixed with the Sensitivity is higher for the lock-in amplifier output, 0.
the Left/Reference S Input 100 signal and its 90° phased Even for amplitudes that are matched within 2%, the sen
shifted signal 104 in the two Phase Sensitive Detectors sitivity of 0 to p is nearly 100 times that of the standard
(PSDs) 106. The internal functions are the same as in the 45 lock-in amplifier configuration.
lock-in amplifier 52 of FIG. 6. FIG. 9 is a functional schematic of a dual lock-in amplifier
The following derivation may be used to determine the 56 with which another exemplary method for measuring the
relationship between the outputs from the lock-in amplifier Coriolis force induced phase shift in accordance with the
54 and the inputs from the displacement gauges 52. Any present invention is implemented. The lock-in amplifier may
Suitable digital or analog processing device 120 may be used 50 be implemented by hardware or Software, or a combination
to perform the calculations. of both. The Signals are moving in the same manner and
Consider the two signals as Sine waves with arbitrary
amplitudes and arbitrary phase difference. Each Signal can have the same definitions as disclosed above. The Left input
be represented as below: 100 is also used as the reference signal. As before, the sine
out 103 is the drive signal, phase locked to the Left input 100
Vie-Ve-A sin (0t 55 signal. In this case, the Left Input 100 signal is mixed with
V,right
in-B sin(otxp) itself and its 90° phased-shifted signal in the two Phase
Sensitive Detectors (PSDs) 106 in the top lock-in amplifier
The output of the Low Noise Differential Amplifier 114 in 58. In the bottom lock-in amplifier 60, the Right Input 102
this case will be V-Vright 60 signal is mixed with the Left Input 100 signal and its 90
At the bottom PSD 106 the following operation occurs: phased-shifted signal in the two Phase Sensitive Detectors
X'=V, (Vr-V,)=A sin otA sin ot-B sin(otxp)
(PSDs) 106. The paired outputs from the non-phase shifted
PSDs 106 and phase shifted PSDs 106 are differentiated in
p 1 2 1
the two Low Noise Differential Amplifiers 114. The DC
X = 5A 1 - cos2Got- 5AB|cos) +cos(2cot + i) 65 components of the Signals are passed by the Low Pass Filters
108 to give the usual lock-in amplifier outputs. The
mathematics, which may be executed by any Suitable digital
 US 6,748,813 B1
11 12
or analog processing device 120, are the same as in the the reference frequency generator 144 will take too long
method outlined above in conjunction with FIG. 7, though reaching the intended frequency. If the Signal frequency
the order in which the operations occur is different. In the experiences frequent Step changes, a PID or adaptive algo
Dual Channel Lock-in technique of FIG. 7, two high level rithm can be used to adjust the reference frequency in a more
Signals, with very Small differences are Subtracted. The responsive manner.
low-level Signal is then multiplied with a high level Signal, In alternative embodiments, the capacitance displacement
which can introduce noise in analog circuits or round off probes 50 may be mounted on piezoelectric actuators that
errors in digital circuits. In the Dual Lock-in technique of would, first, align the capacitance displacement probes 50 in
FIG. 9, the high level signals are first multiplied and the three dimensions. Further, when used with the dual channel
resulting Signals, which are close in amplitude, are then lock-in amplifier or dual lock-in amplifier methods disclosed
Subtracted resulting in an output with lower noise. herein, the piezoelectric actuators can dynamically adjust
A lock-in amplifier's use is most notable with respect to the sensitivity of the of the flow sensor, thereby providing an
measuring a low-level Signal that is buried in noise of a extended range of operation.
much higher amplitude. The lock-in amplifier accomplishes Such dynamic positioning provides compensation for
this by acting as an extremely narrow bandpass filter. The 15 manufacturing variability, particularly the positioning of the
Signal and noise is multiplied by a reference Sine and cosine flow Sensor tube relative to the capacitance displacement
wave, and then passed through a low-pass filter to remove probe. Dynamic positioning also provides compensation for
the reference frequency. The results of the multiply/filter dimensional shifts due to relative thermal expansion of the
operations are DC signals that represent a complex vector various components. Used in combination with the dual
(x+iy). The phase difference between the reference fre channel lock-in amplifier or dual lock-in amplifier, dynamic
quency and the Signal of interest can be determined by positioning allows the two displacement signals to be
atan(y/x). closely matched to provide an adjustable Sensitivity to flow.
In terms of measuring Coriolis force, the phase difference A low sensitivity would be used for high flow conditions
between two Signals of the same frequency is of interest. while high sensitivity would be used for extended low flow
This can be accomplished using dual lock-in amplifiers, 25 conditions, thereby increasing the dynamic range of flow
each driven with the same reference frequency as shown in measurement.
FIG. 10. In the functional Schematic illustrated in FIG. 10, Embodiments of the present invention additionally pro
Left and Right input signals 100, 102 are multiplied by vide improved capacitance measurement techniques,
reference Sine and cosine waves provided by a reference Specifically, a novel geometry of the capacitance displace
frequency generator 144. The input signals 100, 102 are ment probe. Normally, the displacement of an object is
mixed with the sine and cosine signals in PSDS 106, then measured as a distance normal to the capacitance displace
passed through fifth-order bessel IIR low pass filters 148 as ment probe. The displacement may also be measured as a
described in conjunction with FIG. 6, FIG. 7 and FIG. 9. The distance tangential to the capacitance displacement probe.
multiply/filter process described above is performed on the Referring to FIG. 11, this can be accomplished by placing
Left and Right input signals 100,102 with a resulting phase 35 two plates 130 side by side with a uniform gap 132 between
difference output X, Y of each Signal with respect to the the plates 130 and placed near a sensor tube 134 in the plane
reference frequency. The difference between the two output tangential to the motion (indicated by the arrow 136) as
Signals X, Y represents the phase difference between the two shown in FIG. 11. In one embodiment, the plates 130 will be
input signals 100,102. In the case of Coriolis mass flow, this at the same potential and the sensor tube 134 will be at
phase difference represents an indication of mass flow 152. 40 ground potential. The sensor tube 134 is positioned directly
When using lock-in amplifiers to measure the extremely over the gap 132 between the plates 130 with the expected
Small phase differences associated with Coriolis mass flow, motion 136 normal to the gap So that cyclic motion of the
it is necessary to adjust the reference frequency to match the sensing tube 134 will position the tube 134 more closely to
Signal of interest. If the reference Signal is not very close to one plate 130 than the other 130. The relative capacitance is
the Signal of interest, a very low frequency AC signal will 45 measured between each of the plates 130 and the sensor tube
appear at the outputs of the low-pass filters 148. The 134. As the sensor tube 134 moves over one plate 130 or the
frequency of the Coriolis Sensor changes with mass flow, other, the amount of area contributing to the capacitance will
temperature, density and pressure, further complicating the change and thus the relative capacitance measured.
measurement process. An alternative configuration has the gap 132 running
The reference frequency can be adjusted accurately by 50 diagonally across the sensor tube 134 as shown in FIG. 12.
processing the output vector from one of the input signals This allows a less precise placement of the sensor tube 134
100, 102. First, the derivative of the output vector is calcu over the plane of the plates 130. Misalignment of the sensor
lated. This may be accomplished by calculating the complex tube 134 will cause a Smaller mismatch in the Signal as
difference between two consecutive output vectors. Then, compared to the parallel gap 132.
the original output vector is rotated 90 degrees and the dot 55 A further embodiment has the gap 132 in a “saw tooth”
product of this vector and the derivative is calculated, pattern as shown in FIG. 13. This is an improvement over
resulting in an error signal 150 that is provided to the the diagonal gap 132 in that an angular misalignment of the
reference frequency generator 144. The error signal 150 is sensor tube 134 with respect to the gap 132, whether parallel
negative, positive, or Zero, if the reference frequency needs or diagonal, will cause a difference in the rate of change of
to be adjusted down, up or unchanged, respectively. 60 capacitance between the two plates 130. This will introduce
The amount of reference frequency adjustment is depen an unwanted change in phase between the two signals. The
dent on the accuracy of the phase measurement, but "Saw tooth' pattern will average out any angular misalign
generally, the finer the adjustment, the better the accuracy as ment of the Sensor tube 134, providing more Symmetrical
determined by calculating the Standard deviation over a Signals.
number of output Samples. However, the finer adjustment 65 FIG. 14, FIG. 15 and FIG. 16 illustrate an exemplary low
(Small step changes) of reference frequency will be detri flow Coriolis mass flow controller 200 employing capacitive
mental if there are Step changes in the Signal frequency, as pick off Sensors in accordance with an embodiment of the
 US 6,748,813 B1
13 14
present invention. The Coriolis mass flow controller 200 In the embodiment shown in FIGS. 14-16, the conductive
includes a flow sensor portion 202 and a flow control portion plates comprise first and Second plates as disclosed above in
204. A processor either internal or external to the mass flow conjunction with FIGS. 11-13. In the particular embodiment
controller 200 receives an indication of a set point, or illustrated, saw-tooth shaped plates, as illustrated in FIG. 13,
desired mass flow. The Set point value is compared to the are employed. The capacitive pick off Sensors 210 are
actual mass flow as indicated by flow sensor portion 202 to assembled into an integrated sensor block 301 sized to fit
generate an error value. The flow control portion 204 into the sensor enclosure 207, dimensionally referenced to
includes a valve that is manipulated to adjust the flow rate the back wall of the enclosure 207 by press pins 302. The
and minimize the error. The implementation of particular conductive plates 300 of the capacitive pick off sensors 210
control Schemes would be a routine undertaking for one are manufactured on a multilayer printed circuit board So as
skilled in the art having the benefit of this disclosure, and to provide a guard layer to minimize parasitic capacitance
thus, the Specifics of Such an implementation are not and a back contact layer for Soldering to the Sensor block
addressed in detail herein.
The flow sensor portion 202, which is surrounded by an 301. Since the capacitive pick off sensors 210 are required
enclosure 205, includes a sensor tube 206 that is bent into a to operate in a vacuum, low outgassing materials are used in
loop shape, a drive device 208 and two pick off sensors 210 15 the illustrated embodiment. Standard fiberglass materials are
positioned at opposite sides of the sensor tube 206 that not vacuum compatible. Desired material characteristics
measure the displacement of the sides of the sensor tube 206. include that it be vacuum compatible, solderable, bondable
In existing Coriolis devices, the Sensor is typically into multilayers with a low outgassing bond and that it have
enclosed in a welded metal housing. The Sensor tube within a low dielectric constant for Simple guard layer design. In a
the housing also has attached to it displacement or Velocity specific embodiment, commercially available DUROID is
Sensors with wires connecting through feedthroughs to elec used.
tronics outside the housing. The Sensor tube in Such devices In the illustrated embodiment, the conductive plates com
is relatively large and has a resonant frequency that is about prise first and Second plates as disclosed above in conjunc
100 Hz. For Smaller sensor tubes, as in embodiments of the tion with FIGS. 11-13. In the particular embodiment
present invention, the resonant frequency is Somewhat 25 illustrated, saw-tooth shaped plates, as illustrated in FIG. 13,
higher, on the order of 200 Hz, and greater. AS the frequency are employed. The capacitive pick off Sensors 210 are
increases, there will be an increased Viscous damping effect assembled into an integrated sensor block 301 sized to fit
due to the atmospheric conditions inside the Sensor enclo into the sensor enclosure 207, dimensionally referenced to
Sure. By evacuating the enclosure and utilizing vacuum the back wall of the enclosure 207 by press pins 302. The
compatible materials inside the enclosure, the Viscous damp conductive plates 300 of the capacitive pick off sensors 210
ing can be reduced or even eliminated. Thus, in the exem are manufactured on a multilayer printed circuit board So as
plary embodiment illustrated, the sensor tube 206 is situated to provide a guard layer to minimize parasitic capacitance
within a vacuum sensor housing 207. and a back contact layer for Soldering to the Sensor block
The sensor tube 206 is designed to allow elastic bending 301. Since the capacitive pick off sensors 210 are required
orthogonal to a line connecting the legs of the tube's loop. 35 to operate in a vacuum, low outgassing materials are used in
The loop is wide enough to allow elastic twisting about the the illustrated embodiment. Standard fiberglass materials are
centerline of the loop. In order to measure the Coriolis force not vacuum compatible. Desired material characteristics
at low flows, the sensor tube 206 mass needs to be mini include that it be vacuum compatible, solderable, bondable
mized. Tube Sizing is critical Since the tube needs to be into multilayers with a low outgassing bond and that it have
Small, yet still capable of retaining the fluids at extended 40 a low dielectric constant for Simple guard layer design. In a
pressures. It is also preferable for the pick off sensors 210 to specific embodiment, commercially available DRUOID is
be non-contact since any contact with the tube 206 or mass used.
loading on the tube 206 may suppress the Coriolis force. The drive device 208 drives the tube 206 into a bending
Pick off Sensor technologies may include capacitive, mode Vibration, causing it to vibrate. In the illustrated
magnetic, piezoresistive and optical. Piezoresistive, Strain 45 embodiment, the drive device 208 consists of a small magnet
gauge displacement Sensors do contact the tube but at the 304 Soldered on the sensor tube 206 and a small electro
base of the loop where the displacement is minimum and the magnetic coil 306 to alternately push and pull on the magnet
strain is the highest. This would have minimal effect on the 304. In the embodiment shown in FIG. 16, a non-rare earth
tube's vibration. Optical technologies include various laser magnet, and more particularly, a nickel plated Samarium
and white light interferometric displacement techniques, 50 cobalt magnet is used. The Samarium cobalt magnet has a
triangulation techniques, multiple internal reflection and good magnetic Strength to weight ratio. In this embodiment,
beam occultation techniques. Magnetic displacement tech the magnet weighs approximately 20 mg. The magnet 304 is
nologies include Hall effect, eddy current, variable reluc positioned at the top, center of the sensor tube 206 so that the
tance and magnetoresistive techniques. magnetic poles are directed parallel to the tube's preferred
Capacitive pick off Sensor technology is used in the 55 displacement direction.
embodiment illustrated in FIGS. 14-16, because it has the The coil 306 is located outside the sensor enclosure 207,
Sensitivity required to measure the tube displacement, it is coupled to a circuit board 209. The sensor enclosure 207 is
noncontact, and would not be affected by a magnetic drive nonmagnetic and thus transparent to the magnetic fields. The
device. The capacitive pick off sensors 210 each include at coil 306 is an open coil type as opposed to a toroid design.
least one conductive plate 300, which is connected to a given 60 In this embodiment the coil 306 is a commercially available
Voltage potential and Situated adjacent the flow Sensor tube power inductor rated at least 1 mH. The center axis of the
206 so as to define a gap therebetween. The flow sensor tube coil 306 is aligned perpendicular to the face of the magnet
206 is connected to a voltage potential different than the 304. The sensor tube 206 is driven to resonance using the
conductive plate 300. The capacitance between the conduc Signal from one of the capacitive pick off Sensors as feed
tive plate 300 and the flow sensor tube 206 varies due to the 65 back to the coil drive circuit through a phase locked loop
relative motion of the conductive plate 300 and the flow (PLL) function. The function may be implemented as an
sensor tube 206 when the flow sensor tube is vibrated 206. electrical circuit or in Software.
 US 6,748,813 B1
15 16
The sensor tube 206 is mounted to a base portion 212, IP-65/NEMA 4X compliant. An example of such a device
which defines a flow inlet 214 and a flow outlet 216, Such 400 is shown in FIG. 18. In comparison, the embodiment
that a flow passage is provided from the inlet, through the illustrated in FIGS. 14-16 includes a connector 342 coupled
flow sensor tube 206, through the flow control portion 204, to the user interface board 340. As shown in FIG. 18, an
and through the sensor flow outlet 216. The flow control electronics cap 337 is extended to provide space for the
portion 202 includes a meter body 222 with a valve coil 228 additional components required for a particular application.
and coil cover 230 situated therein. A valve stem 232 and Another feature of an o-ring sealed enclosure 205 is that
plunger 234 are situated within the valve coil 228, and a it provides a tertiary fluid containment, the sensor tube 206
valve body 236 is connected to the meter body 222 with a being the primary fluid containment and the Sensor enclo
seal 238 therebetween. A valve seat 240, a spring 242 and an Sure 207 providing the Secondary containment.
orifice 244 are positioned within the valve body 236. End In the event that there are bubbles in the fluid being
blocks 224, 225 are situated on either end of the flow control controlled, the annular opening around the plunger in a
portion 204 with seals 226 provided between the meter body conventional valve restricts the passage of bubbles to the
outlet of the valve. Bubbles will collect at the entrance of the
222 and end block 224, and between the valve body 236 and annular opening to the point that the liquid flow will be
end block 225. In one embodiment, the seals 226 comprise 15 restricted and flow control will be lost. If the annular
electroformed nickel Seals. opening is enlarged, the increased Spacing of the plunger
In an exemplary embodiment, the Coriolis mass flow from the valve coil will reduce the field strength in the
controller 200 is assembled in the following manner. The magnetic circuit and thus reduce the effective force that can
meter body 222 and sensor enclosure 207, as well as a base be achieved in order to open or close the valve against
plate 310, a center post 312 and the sensor tube 206 are hydraulic forces created by the fluid. Thus, in the illustrated
assembled and held in place by a fixture that dimensionally Coriolis mass flow controller 200, a circular hole 246 is
references the sensor tube 206 to the walls of the sensor provided through the plunger 234. The circular hole 246 is
enclosure 207. The remaining parts are indexed by preSS compatible with the shape and size of the bubbles, allowing
pins 330. These parts are then brazed as a single unit. The bubbles to pass more freely through the valve. This mini
magnet 304 is soldered onto the sensor tube 206. The sensor 25 mizes the possibility of flow restriction caused by the
block 301 is assembled and installed into the sensor enclo bubbles. The hole 246 through the center of the plunger 234
sure 207 using press pins 302. The press pins 302 extend minimizes any effects on the magnetic circuit So that the
through the back of the sensor enclosure 207 by approxi force to open and close the valve against hydraulic forces is
mately 0.5 mm. A hermetically sealed connector 320 is maintained.
pressed into the back opening 322 of the Sensor enclosure With typical existing Valves, the valve plunger has a
207. The sensor block press pins 302 and hermetically captive Seat that is made from Some deformable material
sealed connector 320 are laser or e-beam welded to provide that, when pressed against the land of the orifice, will form
a leak tight Seal. A cover 324 is placed over the front Side of a Seal against flow. In the case of a normally closed, Solenoid
the Sensor enclosure 207 in a vacuum environment and laser type valve, the force against the Seat may be generated by a
or e-beam welded into place, providing a vacuum tight 35 Spring balanced So that the Solenoid action lifts the Seat from
environment. The remaining valve components and end the orifice land. In the case of a normally open, Solenoid type
blocks 224, 225 are then assembled with the meter body 222. Valve, the force against the Set is generated by the Solenoid
The electroformed nickel seals 226 may be used, or elasto action and is balanced So that the Spring lifts the Seat from
meric O-rings may be used for calibration purposes, then the orifice when the magnetic field is removed. The seat
replaced with the nickel Seals. The electronics are assembled 40 material may be elastomeric, plastic, or a ductile metal.
and installed on the completed assembly. An O-ring 332 is It is usually preferable to have elastic deformation over
installed on the base plate 310 and the enclosure 205 is plastic deformation So that the Seal is repeatable.
pressed down over the o-ring Seal 332. Cam locks on the Alternatively, hard materials may be used for the Seat and
base plate 310 are rotated to lock down the enclosure 205. land, but fabricated to very tight tolerances including highly
An O-ring 334 is installed on an electronics cover cap 336. 45 matched Surfaces between the Seat and land. This is a high
The electronics cap 336 is positioned over a user interface cost approach. The Spacing between the Seat and land is
connector 338. The electronics cap 336 is pressed into place critical to valve operation Since the magnetic force on the
on the enclosure 205 affecting the o-ring seal. The plunger is not linear with displacement. In the case of a
assembled mass flow controller 200 is then tested and normally open Valve, the normal position of the plunger and
calibrated. 50 thus the Seat relative to the land needs to be optimized in
The exemplary Coriolis mass flow controller 200 has a order to provide the maximum force when the Seat is moved
modular design that provides Several benefits. AS discussed against the land, while allowing the maximum flow in the
above, the electronicS packaging is designed to effect o-ring open position. In a normally closed valve, the force of the
seals at the flow body (between the lower end of the Seat against the land is generated by the Spring. The Spring
enclosure 205 and base plate 310) and at the top to a user 55 force needs to be Sufficient to close against hydraulic forces,
interface cap (between the upper end of the enclosure 205 yet minimized to allow the magnetic force to lift the Seat
and electronics cap 336). The electronics cap 336 is con from the land Sufficient distance to allow maximum flow.
nected to a user interface board 340 internal to the Coriolis Existing devices may use a variety of means to adjust the
mass flow controller 200, which is also connected, to the spacing between the Seat and land, including placing Shims
Sense and control electronics. The electronics cap 336 and 60 under the land or Seat, or having a threaded adjustment
user interface board 340 together define the interface to the screw in the orifice component. As shown in FIG. 17A,
user's electronics. This allows the flexibility to configure the however, a typical threaded adjustment in the orifice does
interface according to the user's requirements without the not seal between the orifice body 250 and the valve body
need to design different Sense and control electronics and 252, leaving a leak path 254 between threads 256. Such a
enclosure for each user configuration. 65 threaded adjustment requires that the threads 256 be sealed
A variant of the user interface cap, for example, will have against fluid leakage. A Separate Seal, Such as an O-ring or
Seals and electrical conduit to provide a device that is gasket provides this Seal.
 US 6,748,813 B1
17 18
In accordance with aspects of the present invention, the ture. The sensor pick off and drive circuit 524 further
orifice 244 and/or land are made of a plastic material, Such provides an output signal to the drive coil 513 for controlling
as VESPEL(R), which is machinable into a threaded compo vibration of the sensor tube 502.
nent with a precision orifice. AS shown in the exemplary The tube is vibrated (in and out of the paper as illustrated
embodiment illustrated in FIG. 17B, the threads 256 are in FIG. 19) using a coil 513 driven with a sine wave at the
machined oversized so that there is an interference fit 258 resonant frequency of the tube 502. The magnetic force
between the orifice body 250 and valve body 252, thus created by the coil 513 (for example, a 1 mH inductor as in
Sealing, eliminating the need for a separate Seal (o-ring or the embodiment described above in conjunction with FIGS.
gasket). The orifice land now is the deformable member 14–16) pushes and pulls on a magnet 514 that is attached to
Simplifying the design and manufacture of the valve Seat 240 the sensor tube 502, thus imparting motion. As the tube 502
and plunger 234 (referring to FIGS. 15 and 16). Vibrates, the amount of infrared light reaching the photo
diodes 512 from the LEDs 510 is increased or decreased as
The present invention, however, is not necessarily limited the sensor tube 502 moves back and forth in the light path.
to any specific valve plunger configuration. In alternative The optical Sense circuit translates the light variations into
embodiments, a pump is used in place of the valve. A Voltages that represent the position of the tube.
metering pump, for example, may be used for fluid control 15
As the sensor tube 502 vibrates, the outputs of the optical
purposes. In particular, a piezoelectric pump may be Sense circuit appear as two Sine waves representing the
employed that includes a plurality of piezoelectric tube motion of the left and right sides of the sensor tube 502. With
portions. The piezoelectric tube portions are controlled in a no mass flow present through the sensor tube 502, the left
manner to cause different tube portions to constrict or and right sides of the tube 502 are in phase, and therefore the
expand, thus allowing the fluid flow to be controlled as two Sine waves are in phase indicating Zero flow. AS mass
desired. flow increases through the sensor tube 502, the phase
FIG. 19 illustrates another exemplary Coriolis mass flow difference between the motion of the left and right side of the
Sensing device in accordance with Still further aspects of the sensor tube 502 increases (linearly with mass flow).
invention. The illustrated Coriolis mass flow sensing device The sensor pick off and drive circuit 524 generates the
500 includes, among other things, alternative structure for 25 sensor drive signal from the optical sense PCB outputs 521,
measuring the tube displacement to detect the Coriolis 522. Therefore, the sensor tube 502, optical pick offs 510,
forces due to mass flow through the tube. Light sources 510 512 and drive coil/magnet system 513,514 make up a closed
are positioned on the Sides near the top or on top of the flow System that Oscillates at a frequency determined by the
tube 502 where the displacement is expected to be the mechanical properties of the sensor tube 502 itself. This
greatest. Photo diodes or other photo detectors 512 can then concept is analogous to an electronic oscillator that uses a
be placed on the opposite side of the tube 502 facing the light crystal instead of a mechanical object (the sensor tube 502).
The DSP PCB 430 and the associated electronics of the
Source 510. The photo detectors 512 are connected to sensor sensor pick off and drive circuit 524 translate the left and
electronics that process the signals received from the photo right sensor tube outputs 521, 522 to a numerical value
detectors 512. The Sensor electronicS may employ digital representing the actual phase difference between the left and
Signal processing devices, Such as the Signal processing 35 right side of the sensor tube 502. This phase difference
methods disclosed in U.S. Pat. No. 5,555,190, or the lock in represents mass flow.
amplifier as disclosed herein in conjunction with the As shown in FIG. 21, the sensor pick off and drive circuit
embodiments illustrated in FIGS. 6-11. Other embodiments 524 includes a stereo A/D converter 550 that is used to
are envisioned that use modal Sensing or Sinusoidal curve fit, sample the left and right outputs 521,522 from the optical
wherein the received signal is compared to a reference using 40 sense PCB 520 for determining the phase difference between
least Squares phase determination, for example. the left and right side of the sensor tube 502, for determining
In one specific embodiment, the light sources 510 and sensor tube 502 vibration frequency, and for determining the
photo detectorS 512 are part of an optical Sense circuit proper sensor tube 502 drive level. An RTD A/D converter
implemented on an optical Sense printed circuit board 552 receives the output from the RTD 542 to measure the
(PCB). The light sources 510 and photo detectors 512 45 sensor tube 502 temperature via the RTD. A multiplying D/A
comprise infrared LEDs and photodiodes to Sense the converter 554 is used to adjust the sensor tube drive level.
motion of the sensor tube 502. As shown in FIG. 19, there The DSPPCB 430 controls the stereo A/D converter 550, the
are two sets of LEDs 510 and photodiodes 512, one set to RTD A/D converter 552 and the multiplying D/A converter
sense each side of the sensor tube 502. 554.
FIG. 20 is a block diagram schematically illustrating 50 Referring back to FIG. 20, the optical drive PCB 540
portions of a Coriolis mass flow controller employing the functions to provide a 90 degree phase shift of the drive
optical Coriolis mass flow sensing device 500 shown in FIG. Signal output, as well as providing attenuation and AC
19. The optical Coriolis mass flow sensing device 500 makes coupling of the optical sense PCB 520 left and right outputs
up a portion of the optical sense PCB 520. The optical sense 521,522. Further, the optical drive PCB 540 provides an
PCB 520 provides left and right output signals 521, 522 55 electrical connection of the RTD 542 to the sensor and pick
(corresponding to the left and right portions of the Sensor off circuit 524 on the motherboard PCB 526.
tube 502) to a sensor pick off and drive circuit 524 residing A discussion of the Signal flow further clarifies the pur
on a motherboard PCB526 via an optical drive PCB 540. An pose of the optical drive PCB 540 and illustrates how the
application and control circuit 528 is also implemented on sensor tube 502 is driven at its resonant frequency. The
the motherboard PCB 526. A digital signal processing (DSP) 60 motion of the sensor tube 502 generates two sine waves (left
PCB 530 includes a DSP processor 532, a flash EEPROM and right output signals 521, 522) via the optical sense PCB
534, a high-speed SRAM 536, and logic and Supervisory 520. These signals pass through to the optical drive PCB 540
circuits 538. A Texas Instrument TMS320C32 processor where they are AC coupled to remove any DC offset, and
operating at 50MHz functions as the DSP processor 532 in attenuated to reduce the amplitudes to that which are appro
one embodiment of the invention. An RTD 542 provides an 65 priate for the inputs of the stereo A/D converter 550 of the
output to the sensor pick off and drive circuit 524 via the sensor pick off and drive circuit 524 on the motherboard
optical drive PCB 540 to measure the sensor tube tempera PCB 526.
 US 6,748,813 B1
19 20
The sensor pick off and drive circuit 524 buffers these The user interface PCB 560 shown in FIG. 22 is an
signals and samples them with the stereo A/D converter 550, optional addition to the motherboard PCB 526 that provides
and also feeds the left side signal 521 through the multiply for a variety of communication protocols. All of the elec
ing D/A converter 554 for adjusting drive gain. After the tronics described to this point are not communication
multiplying DAC 554, the signal is fed back to the optical Specific. To obtain compatibility with various communica
drive PCB 540 where a 90-degree phase lag is induced tion protocols, a unique user interface PCB 560 is provided
before the signal is fed to the sensor drive coil 513. The for each desired protocol using a common user interface
90-degree phase shift circuitry is necessary because a PCB form factor that will plug into the motherboard PCB
mechanical oscillator at resonance requires that the energy 526.
feeding back into the System (via the drive coil and magnet For example, a common communication protocol is the
513, 514) be 90 degrees out of phase with the motion of the HART protocol. The Analog/HART user interface PCB
tube 502. provides a 0(4)-20mA set point input and flow output in
AS will be apparent to one skilled in the art, the addition to the 0(1)-5V input and output already present on
attenuation, AC coupling and 90 degree phase shift could be the motherboard PCB 526. The HART physical layer is also
incorporated on the optical sense PCB 520 or on the moth 15 present on this version, and an isolated power Supply
erboard PCB 526. However, by implementing these func capable of 13VDC to 30VDC main power input is provided.
tions on a separate PCB, the optical sense PCB 520 and FIG. 23 illustrates the HART interface 580. The flow
optical drive PCB 540 may be removed from the system, output signal (O(4)-20mA) 582 is modulated with the appro
allowing other mass flow Sensors to be connected directly to priate carrier to allow the HART communication protocol to
the motherboard PCB 526. The pick off inputs and the drive be transmitted and received on the output signal. The HART
output on the motherboard PCB 526 must compatible with protocol provides a digital interface to the Coriolis mass
the corresponding outputs and drive System of the particular flow controller for the purpose of monitoring data and for
mass flow Sensor to be implemented, or an appropriate calibration and configuration of the device. The flow output
interface must be provided. signal 582 (0(4)-20mA) is also converted to a 0(1)-5V signal
Known Coriolis mass flow sensors do not require the 90 25 584 for flow monitoring of a voltage in addition to current.
degree phase shift on the drive output, Since typical prior art The Set point input provides a jumper to Select between a
Coriolis Sensor pick offs use magnets and coils that are voltage 586 or a current 588 input. The set point input is
Velocity Sensitive (pick off output amplitude is greatest at converted to a voltage (if current input is selected) and
Zero crossing), whereas the optical or capacitive pick offs passed through to the motherboard PCB 526 and is con
disclosed herein are position Sensitive (pick off output nected directly to the motherboard PCB set point input 570.
amplitude is greatest at the peaks). Since Velocity is the The signal that is used for the flow output signal 572 on the
derivative of position, and the derivative of a Sine function motherboard PCB 526 only configuration is converted to a
is a cosine function, and the Sine function is a 90-degree current output on the HART interface 580 and interpreted as
phase shifted cosine, the 90-degree phase shift in Velocity a density output signal 590. The valve override input 570 is
Sensitive pick offs occurs naturally. 35 also passed through directly to the motherboard PCB 526
To initiate vibration of the sensor tube 502, the drive gain Valve override input.
is increased much higher than normal. Ambient vibration The motherboard PCB 526 only configuration shares a
that is always present vibrates the sensor tube 502 mostly at common ground between the power Supply return and all
its resonant frequency. This Small motion is detected by the Signal returns. The power is Supplied using +15VDC and
optical pick offs 510,512 and is used to drive the sensor tube 40 ground. While Separate ground connections exist on the
502 at greater amplitudes (via the high gain drive circuit). motherboard PCB connector for input and output Signals,
When the sensor tube 502 vibration reaches the desired they are electrically the Same point.
amplitude, the drive circuit is Switched to normal gain and The +15VDC input voltage 576 to the motherboard PCB
the DSP PCB 530 takes over sensor tube amplitude control 526 is used directly on all components requiring +15VDC.
via the multiplying DAC 554. Without active control of the 45 The +15VDC is also used to drive two DC-DC Switching
sensor tube drive amplitude, the sensor tube 502 would converters. One is used to convert +15VDC to +5 VDC, the
either Stop vibrating, or vibrate out of control. other to convert +1.5VDC to -9 VDC. All of the electronic
The phase difference, the Sensor tube frequency and the and electrical circuits (including the valve) are powered
sensor tube temperature calculated by the DSP PCB 530 is using these 3 voltage sources (+15VDC, -9VDC and
transmitted to the application and control system 528 via a 50 +5VDC) in an exemplary Coriolis mass flow controller in
4800-baud serial link in the illustrated embodiment. accordance with the present invention. The only connection
FIG. 22 Schematically illustrates aspects of the applica between chassis ground and power/signal ground is a 1M
tion and control circuit. The motherboard PCB 526 also resistor and a 0.01 uP capacitor in parallel.
contains the circuitry for the application and control circuit The addition of the HART interface 580 provides isola
528. A user interface (UI) PCB 560 may be plugged into the 55 tion on the power Supply input 576. The input Voltage range
motherboard PCB 526. The motherboard PCB 526 includes of the HART interface is +13 to 30VDC and is completely
a microcontroller 562, a flash EEPROM 564, a high-speed isolated from the internal Voltage Sources and grounds. A
SRAM 566, and logic and Supervisory circuits 568. One DC-DC converter that converts 13–30VDC (reference num
particular embodiment uses a Motorola 68LC302 ber 592) to 15VDC, provides the isolation. The isolation is
microcontroller, running at 25Mhz. The microcontroller 562 60 galvanic (main power transfer) and optical (feedback). The
controls output of the DC-DC converter is electrically isolated
1. an A/D converter that is used to Sense an analog Set +15VDC and ground.
point input and analog valve override input 570; FIGS. 24A and 24B illustrate the flow sensor portion 600
2. a D/A converter used to output an analog flow Signal of a Coriolis mass flow controller in accordance with an
572; and 65 embodiment of the invention employing optical pick off
3. a D/A converter used to output a valve control Signal sensors. The flow sensing portion 600 shown in FIGS. 24A
574. and 24B is Suitable for use in a mass flow controller Such as
 US 6,748,813 B1
21 22
the controller 200 illustrated in FIGS. 14-16 hereof. sistors. Flow is directly proportional to the differential strain.
Essentially, the flow sensor portion 600 of FIGS. 24A and The phase does not have to be extracted from two separated
24B would be implemented in place of the flow sensor Signals.
portion 202 of FIGS. 14-16. The flow sensing portion 600 Other aspects of the present invention involve Coriolis
includes the flow sensor tube 602, to which a magnet 604 is flow measurement devices employing Straight Sensor
attached. Infrared LEDs 606 and photodiodes 608 are tubes-the flow tube defines a generally linear flow path.
coupled to an optical sense PCB 610, positioned on either FIG. 27 schematically illustrates a straight tube flow sensor
side of the flow sensor tube 602. The flow sensor tube 602, 450 in accordance with embodiments of the invention. First,
magnet 604, LEDs 606, photodiodes 608 and PCB 610 are the tube 452 can be actuated in the usual vertically polarized
all situated within a housing 612, to which a cover 614 is mode by attaching piezoelectric drive devices 454 at each
attached. A 1 mH inductor functions as a coil 616 to drive end of the tube 452. In certain embodiments, the piezoelec
the tube. The coil 616 is positioned outside the housing 612. tric drive devices comprise piezoelectric unimorphs, with
Alternatively, the Sensing tube, drive device and pick off the piezoelectric layer(s) attached to one side of the tube
Sensors all may be contained within the enclosure, or 452. Alternative embodiments are envisioned in which other
Selected components in addition to or in place of the coil 15 piezoelectric drive devices are employed, Such as piezoelec
may be positioned outside the enclosure. For example, tric bimorphs.
certain embodiments may employ an enclosure having a The opposite Side may have either a piezoresistive layer
window defined therein. This allows the light source and/or attached or a piezoelectric layer attached to act as a Sensor
photo detector to be placed outside the enclosure. In Still 456. The pair of unimorphs 454, actuated synchronously,
further embodiments, the Sensor electronics are remoted drives the tube 452 at its resonant mode. AS flow is estab
from the enclosure, for example, using fiber optic cable. This lished through the tube 452, the Coriolis forces will shift the
may be desirable, for example, when the Coriolis mass flow relative Strain on the piezo Sensors 456, creating a phase
Sensing device is employed in a hazardous environment. shift in their output signal.
AS disclosed above, the light Source and detector may Another straight tube Coriolis sensor 451 is schematically
comprise an infrared LED light Source matched to an 25 illustrated in FIG. 28. The straight tube 452 can be actuated
infrared photo diode. The size of the photo diode active in a circularly polarized mode, Similar to that of a two
Surface is close to but slightly larger than the tube diameter. person jump rope. The component of the mass flow vector
As the tube vibrates, it moves through the path between the that induces the Coriolis force is perpendicular to the line of
LED and photo diode, occulting the light from the LED. The the tube 452. Each end of the tube 452 will experience a
tube may be positioned So that the light path between the Coriolis force that will either be oriented in the direction of
LED and detector is partially broken when the tube is at rest. or in opposition to rotation. This will create a phase shift in
As the tube moves about this rest position in a vibratory at opposite ends of the tube 452. The tube may be actuated,
fashion, the light reaching the detector will alternately be at for example, by placing a magnet 460 at the center of the
a minimum or maximum providing a sinusoidal output from tube 452 and driving it in circular oscillation with 2 orthogo
the detector. The relative outputs from each side of the tube 35 nally positioned electromagnetic coils 462. The respective
can be measured for phase differences due to Coriolis drive Signals have a phase difference of 90 degrees. Sensors
induced flow effects. 456 are positioned at either end of the tube 452,
AS noted herein above, the flow Sensing tube may be alternatively, the Sensors 452 could be placed in an orthogo
fabricated from any of a variety of materials. Further, the nal fashion similar to the drive coils 462 and magnet 460 at
flow Sensing tube may comprise a hybrid of materials. An 40 the /3 points on the tube 452. The sensors 456 could be
example of such a hybrid structure is illustrated in FIG. 25. optical, capacitive or electromagnetic in nature depending in
A Coriolis mass flow sensor 700 is illustrated, including a part on the tube material.
silicon frame 702 and a stainless steel tube 704. The Coriolis As an alternative to the magnet 460 and coil 462 drive
mass flow sensor 700 further includes a clamp 706 and arrangement, a piezoelectric tilt actuator attached to each
sensors 708, all of which are also implemented in silicon. 45 end of the tube acts as a driver for this mode in other
Additional materials may be used; for example, the clamp embodiments of the invention. Known piezoelectric tilt
706 may be fabricated from metal, glass, plastic, ceramic, actuators are typically used to dynamically align optical
etc. Thin silicon arms 710 extend from the frame 702 and are mirrors. The typical optical mirror configuration consists of
attached to the sides of the sensor tube 704. threee piezoelectric Stacks arranged in a tripod attached to a
The sensors 708 are piezoresistors implemented in a 50 platform holding a mirror. To drive the tube in circular
Wheatstone bridge at the base of each of the silicon arms oscillation the piezoelectric Stacks are driven with three
710 attached to the sides of the sensor tube 704. These are, Sinusoidal signals, each with its phase 120 degrees advanced
in effect, Strain gauges, measuring the Strain induced by the from the neighbor after it. This would be similar to a
bending of the silicon arms 710. FIG. 26A illustrates a first three-phase motor drive. Since piezoelectric tilt actuators are
Wheatstone bridge 720. A Wheatstone bridge 720 is imple 55 usually expensive and are large compared to a given mirror,
mented at the base of each of the arms 710. The Wheatstone the following alternative is employed in embodiments of the
bridge 720 is typically also implemented in Silicon, being present invention.
deposited or implanted in the silicone frame 702. The Flat piezoelectric unimorphs are considerably leSS expen
Wheatstone bridge 720 includes four bridge resistors R1, Sive than the three-Stack actuator mentioned above. They
R2, R3, R4, of which bridge resistors R1 and R4 are variable 60 typically require a lower Voltage to achieve equivalent
piezoresistors. The Wheatstone bridge 720 further includes displacements and are much Smaller that the Stacked actua
an excitation Supply connection Vs, a Signal return GND, tors. Exemplary tilt actuators 470, 471 are conceptually
and Sensor output Signal connections -Vout and +Vout. illustrated in FIGS. 29A and B. The tilt actuators 470, 471
FIG. 26B illustrates a second Wheatstone bridge 722 that employ, respectively, a three-arm and four-arm flat spiral
is implemented between the two arms 710 to measure the 65 springs 474, 475. Piezoelectric devices are configured on
differential stain between the two arms 710. In the Wheat each arm 476 of the flat spiral spring 474, 475. In the
stone bridge 722, resistors R1 and R2 are variable piezore illustrated embodiment, the Spring 474 has a piezoelectric
 US 6,748,813 B1
23 24
unimorph 472 configured on each arm 476 near the outside 6. The Coriolis mass flow sensor of claim 1, wherein the
ring structure 478 of the spring 474, 475. Piezoelectric or light Source is positioned relative to the flow tube at a point
piezoresistive Sensors are attached to the opposite Side of the wherein displacement of the vibrating flow tube is at a
spring 474 from the piezoelectric actuators 472. The sensors maximum.
Sense the relative phase between the Sensors on each end of 5 7. The Coriolis mass flow sensor of claim 1, wherein the
the tube.
Application of a Voltage to the unimorphs 472 thus results light Source is positioned relative to the flow tube Such that
in displacement of the respective arm 476. With the three the flow tube is positioned partially within the path defined
arm spring 474, the unimorphs 472 are driven by a three between the light source and the light detector when the flow
phase sinusoidal signal as with the three-Stack tilt actuators tube is at rest.
described above, resulting in a generally circular drive 8. The Coriolis mass flow sensor of claim 1, further
motion. The four-arm spring 475 is more complicated in comprising:
Structure, but is simpler in actuation. Instead of a three-phase a frame having the flow tube mounted thereon;
driver, a two-phase driver is required for the four-arm
Structure. Each drive signal is applied to 2 opposing arms wherein the drive device is operatively situated relative to
476. The motion is analogous to applying two sinusoidal 15 the frame for vibrating the frame.
Signals to the X and y inputs to an analog oscilloscope and 9. The Coriolis mass flow sensor of claim 8, wherein the
observing the Lissajous figures. If the two Signals are 90 frame comprises a tube in which the flow tube is situated.
degrees out of phase and are of the same amplitude, result 10. The Coriolis mass flow sensor of claim 8, wherein the
will be a circle. flow tube and the frame are fabricated from different types
The flat spiral spring 474,475 has the advantage over the of material.
sheet type unimorphs 454 disclosed in conjunction with 11. The Coriolis mass flow sensor of claim 10, wherein
FIG. 27, in that the spring 474 will accommodate vertical the flow tube is fabricated of stainless steel.
displacement without the requirement that the diameter
change as in the sheet type 454. Density can still be 12. The Coriolis mass flow sensor of claim 10, wherein
measured by an increase in the Sensor Signal amplitude 25 the flow tube is fabricated of plastic.
driven by an increase in the centrifugal force on the tube. 13. The Coriolis mass flow sensor of claim 10, wherein
This mode of actuation allows for increased flexibility of the frame is fabricated of silicon.
tube material selection. The tube does not have to be a 14. The Coriolis mass flow sensor of claim 1, wherein the
resonating Structure. piezoelectric devices are each connected to a power Source.
The System does not even have to be in resonance Since 15. The Coriolis mass flow sensor of claim 1, wherein the
it can be driven to a continuum of frequencies just as with piezoelectric device comprises a piezoelectric unimorph.
the example of the two person jump rope. 16. A Coriolis mass flow Sensor, comprising:
The particular embodiments disclosed above are illustra a flexible flow tube having first and Second ends, the flow
tive only, as the invention may be modified and practiced in tube defining a generally linear flow path;
different but equivalent manners apparent to those skilled in 35 a drive device including first and Second piezoelectric
the art having the benefit of the teachings herein. unimorphs operatively connected to the first and Second
Furthermore, no limitations are intended to the details of
construction or design herein shown, other than as described ends of the flow tube, respectively, to actuate the flow
in the claims below. It is therefore evident that the particular tube, the drive device including a flat Spiral Spring
embodiments disclosed above may be altered or modified defining a plurality of arms and a plurality of piezo
40
and all Such variations are considered within the Scope and electric devices, each of the arms having one of the
Spirit of the invention. Accordingly, the protection Sought piezoelectric devices attached thereto, and
herein is as set forth in the claims below. first and Second pick off Sensors positioned at the first and
What is claimed is: Second ends of the flow tube, respectively, each of the
1. A Coriolis mass flow Sensor, comprising; 45
first and Second pick off Sensors outputting a signal in
a flow tube; response to movement of the flow tube, wherein a
a light Source positioned adjacent a first Side of the flow Coriolis force established by a flow of material through
tube; the flow tube causes a phase shift between the Signals
a light detector positioned adjacent a Second Side of the output by the first and Second pick off Sensors.
flow tube, the Second Side being generally opposite the 50
17. The Coriolis mass flow sensor of claim 16, wherein
first Side, the light Source and the light detector being the drive device activates the flow tube in a vertically
fixed relative to each other, the flow tube being mov polarized mode.
able relative to the light Source and the light detector; 18. The Coriolis mass flow sensor of claim 16, wherein
and the drive device activates the flow tube in a circularly
polarized mode.
a drive device operatively situated relative to the flow 55
19. A Coriolis mass flow Sensor, comprising:
tube for vibrating the flow tube, such that the flow tube a flexible flow tube having first and second ends, the flow
moves through a path defined between the light Source tube defining a generally linear flow path;
and the light detector.
2. The Coriolis mass flow sensor of claim 1, wherein the a drive device including first and Second piezoelectric
light Source emits infrared light. 60 unimorphs operatively connected to the first and Second
3. The Coriolis mass flow sensor of claim 2, wherein the ends of the flow tube, respectively, to actuate the flow
light Source comprises an infrared LED. tube in a circularly polarized mode,
4. The Coriolis mass flow sensor of claim 3, wherein the first and Second pick off Sensors positioned at the first and
light detector comprises an infrared photo diode. Second ends of the flow tube, respectively, each of the
5. The Coriolis mass flow sensor of claim 4, wherein the 65 first and Second pick off Sensors outputting a signal in
photo diode defines an active Surface larger than the diam response to movement of the flow tube, wherein a
eter of the flow tube. Coriolis force established by a flow of material through
 US 6,748,813 B1
25 26
the flow tube causes a phase shift between the Signals 22. The Coriolis mass flow sensor of claim 21, wherein
output by the first and Second pick off Sensors. the piezoelectric devices are each connected to a power
20. The Coriolis mass flow sensor of claim 19, wherein Source Such that each of the piezoelectric Stacks is driven
the drive device comprises: with a sinusoidal Signal having its phase 120 degrees
a flat Spiral Spring defining a plurality of arms, and advanced from the Sinusoidal signal applied to an adjacent
a plurality of piezoelectric devices, each of the arms piezoelectric device.
having one of the piezoelectric devices attached 23. The Coriolis mass flow sensor of claim 20, wherein
thereto. the plurality of arms comprises four arms.
21. The Coriolis mass flow sensor of claim 20, wherein
the plurality of arms comprises three arms. k k k k k