A mass flow meter for placement in line within a pre-existing process
line. The flow meter having a conduit forming a substantially free
floating spiral or circular loop which is symmetrical about the
axis line defined by the process line. A driving transducer extending
radially from a bracket on a support beam which is positioned along
the axis line and attached to the inlet and outlet end of the conduit.
The driver imparting an alternating deflection to the loop which
is substantially perpendicular to the fluid flow within the loop
and parallel to the axis line. Sensing transducers are positioned
along the periphery of the loop, displaced equidistant from the
driving transducer along its circumference for determining the deflection
signature of the loop. The deflection of the loop in response to
the fluid reaction forces is measured without reference to a specific
fixed axis or position of the loop. This acceleration signature
is correlated to the mass flow rate of the fluid through the conduit.
1. An apparatus for measuring the mass flow of a fluid stream comprising:
a conduit having an inlet end and an outlet end, each said end fixed
with respect to one another and positioned substantially along a
single axis; a substantially free-floating continuous flow tube
forming at least one loop spiraled between said inlet and said outlet
ends, whereby the continuous flow tube is substantially free of
restrictions or constraints along its spiraled length offset from
the single axis, and said loop being symmetrical about said single
axis between said fixed inlet and outlet ends; a driving transducer
imparting an oscillation to said loop in a direction perpendicular
to the flow within said loop and parallel to the single axis; and
means for sensing the deflections of said loop in response to the
reaction of the flow to the oscillation of said driving transducer,
said sensing means positioned in opposite radial directions from
said driving transducer along the periphery of said loop.
2. An apparatus as claimed in claim 1 further comprising a support
beam positioned substantially along said axis between said inlet
end and said outlet end; and a mounting bracket on said beam and
in the plane of said loop, said bracket having a plurality of radially
extending arms for support of said driving transducer and said sensing
3. An apparatus as claimed in claim 1 further comprising a second
driving transducer positioned diametrically opposite of the first
mentioned transducer on said loop and imparting a corresponding
oscillation to said loop in substantially the same rotational direction
as said first mentioned transducer.
4. An apparatus as claimed in claim 1 wherein said driving transducer
comprises an electromagnetic coil excited by an alternating electrical
current, said output of said coil having a frequency corresponding
to the natural resonant frequency of the loop, such that the oscillation
of the of the loop induces the corresponding Coriolis reaction force
from the fluid with said loop.
5. An apparatus as claimed in claim 1 wherein said sensing means
comprises an accelerometer mounted directly onto the conduit loop,
said accelerometer being substantially immune to common mode vibrations
unrelated to the fluid reaction against the loop.
6. An apparatus as claimed in claim 1 further comprising a support
beam attached to said inlet end and said outlet end and extending
substantially along said axis passing through the plane of said
loop, said loop being spiraled concentrically about said support
7. An apparatus as claimed in claim 1 wherein the periphery of
said spiraled loop is substantially circular when viewed along said
8. An apparatus as claimed in claim 7 wherein said circular portion
of said loop is formed substantially in a single plane.
9. An apparatus as claimed in claim 1 wherein said loop is formed
in a single plane substantially perpendicular to said single axis.
10. An apparatus for measuring the mass flow of a fluid in a defined
fluid stream or pipeline comprising: a conduit having an inlet end
for receiving the flow from the fluid stream and an outlet end for
returning the flow to the fluid stream, said inlet end and said
outlet end positioned substantially along an axis defined by the
defined fluid stream or pipeline, said conduit substantially free
of restrictions or constraints for at least a portion of its length
between the inlet end and the outlet end, said portion including
a free floating continuous circular shaped loop, said loop lying
substantially in a plane perpendicular to the axis with said axis
passing through the center of the circle formed by said loop; a
support beam positioned along said axis and passing through said
loop, said support beam connected at respective opposite ends thereof
adjacent said inlet end and said outlet end; a mounting bracket
attached to said support beam at a position substantially in the
plane of said loop, said bracket having a plurality of radially
extending arms; at least one driving transducer mounted on one said
arm and positioned adjacent to said loop said driving transducer
imparting an oscillatory displacement to said loop, the displacement
imparted in a direction substantially parallel to the axis line;
and means for sensing the deflections of said loop due to the reaction
of the flow against said loop in response to the oscillatory displacement,
said means sensing said reaction without reference to a specific
preset or fixed position of said loop, said sensing means mounted
on said radially extending arms at positions adjacent the loop and
displaced equidistant and in opposite directions from said driving
transducer along the periphery of said loop.
11. An apparatus as claimed in claim 10 further comprising: a second
driving transducer mounted on one of said radially extending arms
and positioned adjacent to said loop diametrically opposite from
the first mentioned driving transducer, said pair of driving transducers
imparting oscillatory displacement to said loop in the same rotational
direction about the center of said loop.
12. An apparatus as claimed in claim 11 wherein said sensing means
includes a pair of piezo electric transducer type accelerometers.
13. An apparatus for measuring the mass flow within a pre-existing
defined fluid stream, by measuring Coriolis reaction forces of the
fluid on the apparatus, comprising: means defining a conduit having
an inlet and an cutlet for receiving and exhausting flow from the
fluid stream, said inlet and outlet positioned substantially in
a straight line and each positioned along the defined fluid stream;
a continuous flow tube including a substantially free floating loop
formed between said inlet and said outlet, said loop being substantially
symmeterical about and substantially free of restrictions or constraints
along its periphery offset from said straight line and having a
first and second gently bent portions, said first portion for directing
the flow from said inlet into said loop, said second portion for
directing the flow from said loop into said outlet; a support beam
extending substantially along said straight line and attached at
opposite ends to said conduit means adjacent to said inlet and said
outlet; means for imparting an oscillation perpendicular to the
flow at a point on said loop, means for sensing the movement of
the loop due to the reaction of the fluid to said oscillation means,
said sensing means positioned adjacent to the periphery of said
loop and displaced equally and in opposite directions along said
periphery from said oscillation means on said loop.
14. An apparatus for measuring the mas flow of a fluid stream comprising:
a conduit having an inlet end and an outlet end positioned substantially
along a single axis line and fixed with respect to one another;
a substantially continuous flow tube spiraled about said axis line,
said spiral of said flow tube having a loop of an arc of at least
270.degree. formed about said axis line, an inlet section for directing
the flow into the loop from the inlet end of the conduit and an
outlet section for directing the flow from the loop into the outlet
end of the conduit, the flow tube being substantially free of restrictions
or constraints along its continuous length so as to be substantially
free-floating between said inlet and outlet ends; means to oscillate
the flow tube transverse to the direction of flow within said loop;
and means to sense the reaction of the flow on said free-floating
flow tube in response to the imparted oscillation, said sensing
means positioned on opposite sides of said oscillation.
BRIEF SUMMARY OF THE INVENTION
This invention relates to a mass flow meter which measures Coriolis
or gyroscopic type reaction forces to determine the mass flow of
a fluid or slurry within a conduit. Paricularly this invention incorporates
a conduit loop having an inlet end and an outlet end positioned
substantially along a single axis which is typically defined by
a line of existing piping. The loop is alternately deflected in
a direction orthogonal to the flow within the conduit. The alternating
deflections or oscillations of the conduit imparts a transverse
angular momentum to the fluid flowing through the loop. The fluid
reacts with a repetitive and measurable force against the wall of
the conduit causing a transverse deflection of the loop. The reaction
of the fluid on the conduit is proportional to the magnitude and
direction of the fluid mass flow.
BACKGROUND OF THE INVENTION
The invention relates to a mass flow metering device which operates
within a defined fluid stream. Such metering devices are desirably
constructed without internal moving parts which may be contaminated
by the fluid within the stream. The principle of the invention is
based on the known fact that a fluid flowing through a conduit or
tube which experiences an acceleration orthoginal to the direction
of its flow, will interact with the conduit wall with a reaction
force which is directly proportional to the mass flow of the fluid
within the conduit. The reaction force generated by the fluid against
the conduit is generally referred to as a Coriolis force.
Various issued patents describe mass flow meters which utilized
the measurement of the fluid reaction forces to determine the mass
flow rate. These patents teach various conduit designs and configurations,
various means for measuring the reaction forces and various ways
of determing the mass flow.
Roth, U.S. Pat. No. 2865201 teaches a gyroscopic type flow meter
which directly measures the magnitude of the reaction forces on
the conduit. Since these forces are created by a continuous oscillation
of the conduit, the Roth design is impractical. Similar conduit
designs are found in Roth, U.S. Pat. No. 3276257 and Henderson,
U.S. Pat. No. 3108475. The sensitivity of the reaction force measurement
in all of these conduit designs is greatly influenced by the oscillatory
fluctuations of the meter conduit and by environmental vibrations.
A series of patents, U.S. Pat. Nos. 3261205 3329019 and 3355944
to Sipin teach the measurement of the fluid reaction forces due
to an imparted transverse vibration on a straight conduit, a curved
conduit and a U-shaped conduit. The earlier conduit designs in this
series attempt to directly measure the reaction forces on the conduit
and, therefore, were subject to the same substantial sensitivity
deficiencies due to external vibrational influences found in the
patents discussed above. In the curved and U-shaped conduit designs,
the imparted oscillation creates a torsional bending moment about
an, ideally, fixed axis. In the U-shaped design the sensors were
required to be referenced to the actual motion of the tube and to
a fixed or stationary position. In a working environment each of
the Sipin conduit designs are extremely noisy in operation and,
basically, ineffective due to inacuracies created by vibrations
of the flow meter and the references of the sensors tube unrelated
to the fluid reaction force. The drivers, which impart the oscillatory
motion to the conduit, are attached to an external casing of the
meter. The internal and external vibrational effects causes substantial
output deficiencies in the reaction force sensing means and, therefore,
greatly effect the calculation of the mass flow rate.
In Smith, U.S. Pat. No. 4109524 an attempt was made to separate
the oscillation means from the force measurement system. The flow
meter disclosed in this patent is cumbersome in application and
does not effectively reduce the vibrational effects on the reaction
force sensing means.
The first patent to recognize the need for vibrational and noise
immunity on the sensing means is Cox et al, U.S. Pat. No. 4127028.
In Cox each reaction force sensor is referenced to two adjacent
cantalevered tubes. The two tubes are oscillated simultaneously
in opposite relative directions and, ideally, at the same resonance.
The external vibrational influences on the two tubes are intended
to be self-cancelling when viewed by the sensors referenced to both
tubes. However, the driving means in this design is mounted on a
long cantilever arm and includes a large weight at the end of the
arm. This structure produces an extremely low vibrational resonance
and greatly limits the ability of the cantalevered tube to oscillate
about a fixed reference axis. Environmentally induced vibrations,
as well as vibrational effects of the driving means continue to
influence the Cox measurement sensitivity by affecting the positioning
of the tubes differently.
The same deficiencies found in Cox '028 in its reaction force sensing
are found in the Smith, U.S. Pat. No. 4187721 and its corresponding
Reissue No. 31450. Smith, U.S. Pat. No. 4422338 attempts to
enhance the sensitivity of the meter by using a frame which surrounds
the oscillating tube to act as a fixed sensor reference. In addition,
the Smith '338 design utilizes velocity type sensors to create an
adjoining reference system such that the zero or reference position
of linear type sensors, which record the tube motion due to the
fluid reaction forces, is continually adjusted in response to vibrational
influences on the meter. However, since the rotational axis of the
cantalevered flow meter tube and mounting frame is not stationary,
due to the vibrational effects on the meter structure. The effect
of adjusting the reference plane of the reaction force sensors,
therefore, is minimal. Commonly assigned copending application Ser.
No. 809659 submitted to the Patent Office on Dec 16 1985 teaches
a conduit design which is not cantilevered and is driven preferably
directly along the axial line of the pipeline of the defined fluid
stream. The structure of this invention overcomes many of the prior
art deficiencies in sensing.
It is important to note that in all of the known flow meter designs,
as long there is an increasing gradient of transverse velocity from
the entrance of the flow meter tube to a point of maximum velocity
and a decreasing transverse velocity gradient from the maximum point
to the outlet, that there will be a decreasing transverse reaction
or Coriolis force gradient in one direction from the inlet to the
point of maximum deflection or velocity and a transverse force gradient
in the opposite direction from the maximum point to the outlet.
The measurement or sensing of these reaction forces created by the
Coriolis reaction of the fluid maybe correlated to the mass flow
rate within the tube.
The prior art of this type flow meter exhibits significant deficiencies
in their determination of the fluid reaction on the tube. These
deficiencies are directly related to the geometry of the meter and
its sensing technique. It is difficult to isolate the oscillating
motion of the flow meter tube created by the fluid reaction forces
due to the environmental vibrations encountered by the conduit (or
vibrations created by the meter itself).
The typical industrial environment in which the flow meter operates
is subject to substantial vibrational influences due to the presence
of rotating machinery within the process line in which the meter
is located. External temperature influences, as well as, internal
pressure and temperature fluctuations adversely affect the reliability
and the sensitivity of the known meter designs.
Additional problems which effect the sensitivity of this type flow
meter relate to the utilization of these instruments "on line"
within an existing piping system in an industrial process. Impedance
of the fluid flow caused by the flow meter may significantly hamper
the efficiency of the industrial process.
Furthermore, flow meters of this type have a tendency to become
complex, bulky and expensive, all of which adversely affect the
applicability of the Coriolis or gyroscopic measurement technique
in many instances.
OBJECT OF THE INVENTION
It is therefore an object of this invention to provide a mass flow
meter that overcomes some of the deficiencies of the prior art and
which may be easily positioned "on-line" within an existing
pipe or process line.
It is also the object of this invention to provide a flow meter
structure which effectively increases the measurablility of the
fluid reaction force on the conduit while eliminating environmental
and structural limitations that affect the reaction force sensing
and its correlation to the mass flow rate.
It is a further intent of the present invention to provide a mass
flow meter that is substantially insensitive to temperature and
pressure fluctuations and to typical industrial environmental vibrations.
SUMMARY OF THE INVENTION
The preferred embodiment of the present invention incorporates
a flow meter conduit or tube positioned within a pre-existing pipe
line or defined fluid stream having an inlet and an outlet end arranged
axially along the pipe line of the fluid stream. Intermediate between
the inlet and outlet, the flow meter tube is spiraled symmetrically
about the axis line such that the conduit forms a substantially
free floating loop. In one embodiment of the invention the loop
lies in a plane substantially perpendicular to the first axis (the
plane being defined by the "Z" and the "Y" axes).
The loop is free floating having no defined axis of rotation and
is relatively free of restrictions or constraints along all points
of its periphery.
A fluid stream enters through the inlet of the meter, proceeds
around the loop (such that it is traveling in a direction perpendicular
to the axis of its input flow), exits the loop through the outlet
and returns into the defined fluid stream. A support beam, lying
substantially along the first axis and passing through the geometric
center of the loop is secured adjacent to the inlet and outlet ends
of the flow meter conduit. A mounting bracket secured to the support
beam incorporates radially extending arms which position a single
or, in the alternative, a pair of driving transducer(s) on the periphery
of the loop. Each driver imparts an oscillating deflection to the
loop in a direction substantially perpendicular to the flow within
the loop and parallel to the X-axis. Sensing transducers may be
mounted radially from the bracket and positioned adjacent to the
outside edge of the loop. Sensors may also be mounted directly onto
the periphery of the loop without support from the brackets. Two
or more sensors on opposite sides of the center oscillation are
used to process and correlate the information relating to the deflection
signature of the conduit loop due to the reaction forces of the
fluid on the conduit.
The radially positioned sensing transducers produce serial information
as to the specific displacement cycle of the conduit resulting from
the fluid reaction forces. This information can be correlated in
the microprocessor in any convenient manner to provide an accurate
determination of the mass flow rate.
The support beam may be rigidly mounted or have a spring damping
arrangement to reduce vibrations which may be translated to and
from the mounting system. However, due to the radial sensing configuration
contemplated by this invention, the external vibration translated
to the beam and mounting bracket are effectively self cancelling.
A free floating loop arrangement has the advantage of reducing
the spring constant of the conduit which acts to resists deflection
of the loop due to the fluid reaction forces. This spring constant
reduction increases the sensitivity of the meter. The sensing capabilities
of the meter are also increased, as compared to the known designs,
since the flow meter loop is not cantalevered or subject to an extreme
bending moment about a fixed mounting position. The softer spring
constant, also, permits the use of heavier or stronger wall materials
when designing the flow meter conduit, increasing longevity and
permitting use with higher operating pressures and temperatures.
The symmetrical positioning of the loop also optimizes the center
of gravity about its central axis.
A free floating loop, as compared to a cantalevered U-shaped form,
eliminates the need for measurements about a fixed rotational axis.
The reactions of the flow meter conduit, as measured by the sensors,
are not referenced to a specific fixed structure or axis and, therefore,
vibrations created by the structure or by environmental machinery
do not alter a fixed reference location. Additionally, radial positioning
of the drivers and the sensors effectively cancel these external
vibrations and, therefore, do not create a significant effect on
the sensor measurements.
The acceleration imparted to the fluid by the driver is, desirably,
at a maximum at a point along the axis line defined fluid stream
and is directed parallel to that line. Common mode vibrations from
the driver are translated axially through this system. Additional
vibrational influences do not substantially affect the fluid flow
before or after passing through into the flow meter.
Also, the transverse mounting of the loop is substantially immune
to noise and other translated vibrational forces. Transverse mounting
with respect to the fluid stream creates a very stable plane, such
that no one portion of the flow meter conduit is subject a to greater
vibrational effect than another.
In line mounting of the flow meter conduit, also, brings the inlet
and outlet of the flow meter closer together. Therefore, the conduit
contemplated by this invention substantially reduces the size of
the meter between the inlet and the outlet as well as the size of
the casting of the covers and mounting brackets required.
Further objects and advantages will become apparent to those skilled
in the art by particularly describing the preferred embodiments
of the invention.
For the purpose of illustrating the invention, there is shown in
the drawings a number of forms which are presently preferred; it
being understood, however, that this invention is not limited to
the precise arrangements and instrumentalities shown.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a single loop embodiment in accordance
with the teachings of the present invention.
FIG. 2 is a side view of the embodiment in FIG. 1.
FIG. 3 is a perspective view of the embodiment in FIG. 1 referencing
a three-dimensional coordinate system.
FIGS. 4a and 4b show an alternate sensor embodiment mounted directly
on the flow meter conduit.
FIG. 5 shows an alternate embodiment of the flow meter to that
shown in FIGS. 1 2 and 3.
FIG. 6 shows a two driver embodiment of the flow meter shown in
FIG. 7 shows the relative reaction forces effecting the conduit
DETAILED DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the flow meter of this invention comprises
a conduit or tube which is generally referenced by the numeral 10.
This conduit 10 is to be positioned "in line" within a
defined fluid stream or pre-existing pipe line (not shown).
Referring to FIGS. 1-3 the conduit 10 is provided with an inlet
12 and an outlet 14 at respective ends. The inlet 12 and outlet
14 are positioned substantially along a single axial line which
is defined by the pre-existing pipe line and is referenced as the
X-axis 16. Intermediate of the inlet 12 and outlet 14 the conduit
10 is formed into a spiral which, as shown, forms a loop 18. The
referenced coordinate system referred to in this text is shown in
FIG. 3. The Y-axis is referred to by the numeral 20 and the Z-axis
being 22 in the three dimensional system shown.
The inlet portion 24 of the conduit 10 between the inlet 12 and
loop 18 and its corresponding outlet portion 26 from the loop 18
to the outlet 14 are formed through the use of gently bent portions
which turn the direction of the fluid flow approximately 90.degree.
(when viewed from above the X-Z plane). These inlet and outlet portions
24 26 of the spiral design in FIGS. 1 2 and 3 are formed to minimize
restriction of the fluid flow through the conduit 10. The actual
shape of these portions 24 26 will vary depending on conduit diameter,
the intended working fluid and the length of the spiral of the loop
along the X-axis 16.
A mounting bracket 28 is positioned at the center of the loop 18.
Supporting arm 30 extends radially from the mounting bracket 28
and is positioned substantially along the Y-axis 20 to a position
directly adjacent to the periphery of the loop 18. A driving transducer
32 is mounted on the end of support arm 30. The driver 32 may be
of any conventional design such as an electromagnetic coil excited
by an alternating current (See FIG. 2). The driver 32 when excited
to oscillate the loop 18 imparts a deflection to the loop 18 substantially
parallel to the X-axis 16. The oscillation of the loop 18 induces
the alternating change in the angular momentum of the fluid within
the conduit 10. Alternately, driver 32 substantially deflects the
loop 18 perpendicular to the Y-Z plane and about the Z-axis 22
although these references are not critical to the invention.
The mounting bracket 28 is supported on a beam 36 which passes
through the center of the loop 18 and extends substantially along
the X-axis 16 and is attached to the inlet 12 and the outlet 14.
This structure references the driver 32 to a single point which
is substantially at the center of the loop 18.
The loop 18 is substantially symmetrical about the reference beam
36 (and the X-axis 16) and, therefore, automatically compensates
for thermal expansion of the conduit 10 due to temperature variations
in the fluid or the environment. Expansion or contraction of the
conduit loop 18 or the bent portions 24 26 will result in equivalent
changes in the loop's dimensions along its periphery and its position
with respect to the X-axis 16.
It should be noted that the plane of the loop 18 need not be perpendicular
to the X-axis 16 (FIGS. 1 2 and 3). The only limitation is that
the driver 32 deflects the conduit 10 in a direction which is substantially
perpendicular to the flow within the loop 18 and at the same time
parallel to the X-axis 16.
Sensing transducers 38 and 40 may be mounted radially from the
mounting bracket 28 on support arms 39 41 respectively. These
sensors 38 40 are, preferably, located at the position adjacent
to the maximum measurable deflection of the loop 18 created by the
reaction of the fluid to the transverse acceleration created by
the driver 32. Typically this position is a along the circumference
of the loop 18 approximately 90.degree. from the driver 32. These
sensors or switches may take any known form such as linear, optical,
In an alternate embodiment of this invention a piezo transducer
type sensor 38', 40' may be directly attached to the loop 18 (as
shown in FIG. 8) or mounted by a clip (not shown) rather than be
supported on arms 39 41. Although any type sensing mechanism may
be utilized these piezo self referencing sensors, which are accelerometers,
are preferred. This type of sensing transducer, particularly shown
in FIGS. 4a and 4b, converts high mechanical vibrational energy
into an electrical pulse where the relative motion of the loop 18
becomes proportional to the acceleration of the tube 10 at the reference
position. The piezo transducer is generally used together with a
low pass filter to eliminate vibrational frequency components in
the neighborhood of the natural resonance frequency. Such filtering
may be performed simultaneously by a microprocessor while calculating
the mass flow calculations.
The mechanical structure of a typical accelerometer is shown in
FIGS. 4a and 4b. A ceramic body piece 42 is formed with its electrical
components 42a, 42b, 42c being mounted within a thick film or directly
onto the only surface. The ends of the sensor 38 are mounted to
the conduit wall 10. The body 42 is provided with a central, typically,
tungsten filled epoxy mass 46. The central mass 46 is mounted to
a film which is supported on the body 42 by washer 48. The alternating
deflections of the loop 18 due to the reaction forces of the fluid
move the central mass 46 in alternating directions placing the piezo
element crystal in alternating tension and compression modes. The
output of this arrangement produces an electrical signal simulating
the deflection signature of the fluid reaction forces on the conduit
It is desired that the physical dimensions of the loop be such
that its natural resonant frequency does not correspond to the resonant
frequencies of machinery found in the surrounding environment or
utilized in the process line. Typical industrial machinery operates
at a resident frequency of 50-60 Hz. The combination of these environmental
vibrations on the operating flow meter may create substantial discrepancies
in the measurements of the sensing transducers 38 40.
The alternate embodiments of the invention included in FIGS. 5
and 6 show, generally, a loop 18 and 118 respectively, formed substantially
in a single plane (Y-Z plane). The imparted oscillation created
by the driver(s) 32 in these figures is parallel to the X-axis 16
perpendicular to the fluid flow within the loop 18 and 118 and substantially
perpendicular to the Y-Z plane. Thus the deflections of both sides
of the loop are basically away from the Y-Z plane although this
plane is not particularly referenced by the sensors.
The embodiment in FIG. 6 includes a second driver 32' which is
mounted from the bracket 28 by a second support arm 30'. The two
drivers impart 32 32' deflections of the single plane loop 18'
such that the loop 18' is deflected substantially simultaneously
away from the Z-axis 22. Again, this axis is not referenced by the
sensors 38', 40' for a proper calculation of the mass flow.
Both embodiments of the flow meter in FIGS. 5 and 6 utilize the
substantially free floating loop design having a reduced spring
constant. The torsional bending of the loop 18' is reduced as compared
to the alternate embodiment 18 (in FIGS. 1-3) since the conduit
is in the same plane and not spiraled about the X-axis.
FIG. 9 shows the integrated reaction forces (Fm and Fm') on the
loop 18 in response to the transverse imparted deflection (VC).
This integrated reaction force (Fm) is basically the same for all
embodiments shown in the drawings and creates a torque (Tm) substantially
about the Y-axis 20.
In operation, a fluid stream is supplied to the inlet 12 travels
around loop 18 and is returned into the stream through the outlet
14. The fluid is subject to an alternating transverse acceleration
caused to the loop 18 by the excitation of the driver 32. A maximum
deflection occurs in one direction and then a reverse deflection
occurs to a similar maximum. The transverse acceleration imparted
to the fluid flowing in the conduit 10 results in reaction force
which deflects the loop 18 on opposite sides of the driver 32
away from its stationary position. The sensors 38 40 (or 38', 40')
are preferably positioned at points of maximum displacement of the
loop 18 caused by this fluid reaction force.
The deflection of the loop is measured with respect to time in
order to determine the signature of both sides of the loop 18 due
to the oscilating accelertion force. The transverse acceleration
of the flowing mass within the loop 18 will cause a differential
deflection on opposite sides of the driver 32. The deflection of
the loop 18 between the inlet portion 24 and the driver 32 will
lag or lead the deflection between the driver 32 and the outlet
portion 26 depending on the oscillation directions. This is due
to the spatial accelerations and decelerations of the mass flow
in these respective loop 18 segments. The signature information
provided by the sensors 38 40 with respect to this phase motion
of the loop 18 is fed into a microprocessor. Noise vibrations can
be removed simultaneously from these signals as can an indication
of the validity of the signature cycle. The sensor data may then
be directly correlated to determine the mass flow. Each of these
calculations and electronic filterings can be performed by any suitable
Suitable sensing means can be of either the analog or digital type.
Analog sensors are used to measure the phase difference of the differential
deflection of the two sides of the loop 18. Information relating
to the phase of the two simultaneous outputs cancels the effects
of structural changes in the physical positioning of a loop 18 with
respect to the sensing system. This type sensing system dynamically
responds to structure variations in the flow meter due to the changes
in ambient conditions and, also, to common dynamic continuous or
spike vibrational effects.
The electrical circuitry utilized to control the energization of
the driving transducers and to measure the loop 18 deflections,
its time phase relationship to the driving force, and to receive
and process the resulting signals may be performed in a microprocessor.
The driver circuit is a conventional mechanical feedback multivibrator
which runs at the resonant frequency of the mass being driven. Typically,
A MOSFET bridge excites the coil which drives the magnet. Conventional
coil/acceleometer feedback can be used but a combination of piezo/coil
or piezo/crystal can be used to eliminate some electromagnetic common
Since it has become clear that mechanical noise is affecting known
flow meters, it is desirable to produce a narrow band signal to
eliminate unwanted noise caused by vibrations actually sensed by
the sensors. This is in addition to differential noise cancellation
between the sensors and the driver. The narrow band filters at the
output of the piezo x-tal type preamp should be very tightly matched
in characteristics and physically tied together for temperature
tracking, so that any phase shift in the filters will be identical
and the integrity of the desired mechanical phase shift is maintained.
In a circular design common industrial environmental vibrations
effect the loop 18 equally at all locations rather than to one portion
to a greater extent than another. The temperature and vibration
error, which unequally effect different portions of the apparatus
in known Coriolis type flow meters, may cause the offset zero reading
during calibration and use of these known meters. The structure
of this invention inherently provides the, so called, common mode
rejection of these environmental vibrations and substantially increases
the sensitivity and accuracy of the meter. The free floating design,
therefore, permits the application of the invention in otherwise
normally unacceptable industrial environments.
The present invention may be embodied in other specific forms without
departing from the spirit or essential attributes thereof and, accordingly,
reference should be made to the appended claims, rather than to
the foregoing specification, as indicating the scope of the invention.