A Coriolis-type mass flow meter for use in sanitary applications.
A pair of sensing tubes have their ends rigidly mounted within bores
formed within identical inlet and outlet fixtures. The ends of the
tubes fit snugly within the bores and are ends brought out flush
with the ends of the bores. The flush ends of the tubes are secured
to the bores by means of welding. An annular flange is formed about
the flush tube ends of the inlet and outlet fixtures to allow easy
assembly and removal of the mass flow meter from its associated
fluid flow pipeline or conduit. The inlet and outlet fixtures and
tubes preferably are formed from a non-reactive, weldable material
such as stainless steel. The mounting arrangement of the tubes within
the bores of the inlet and outlet fixtures makes it easy to secure
the tube ends to the fixtures by means of welding in a readily accessible
location. These welds can then be easily smoothed or polished to
remove any possible obstructions to fluid flow or hiding places
for contamination. This arrangement results in a mass flow meter
which is acceptable for sanitary applications, e.g. the measuring
of mass flow and/or density of foodstuffs.
What is claimed is:
1. In a Coriolis-type mass flow meter of the type having an inlet
and an outlet, and at least a pair of tubes disposed between the
inlet and outlet to allow fluid to flow therebetween, and means
for vibrating the tubes and means for measuring the frequency of
vibration of the tubes and for deriving therefrom a measure of the
mass of fluid flowing through the tubes, the improvement comprising:
an inlet fixture and an outlet fixture for rigidly holding ends
of the pair of tubes, the inlet fixture and outlet fixture being
identical in structure, each fixture having a pair of separate and
unconnected bores formed therein for receiving the ends of the tubes,
the wall of a bore being in direct contact with an outer surface
of its associated tube, each tube being arranged with its end substantially
flush with an end of its associated bore, the tubes and fixtures
each being formed from a weldable material and the end of each tube
which is flush with its respective bore being secured to the bore
by welding and the weld between each tube end and its associated
bore having a substantially smooth surface.
2. The meter of claim 1 wherein the inlet fixture and outlet fixture
each include an annular flange formed about each pair of bores in
proximity to the ends of the tubes disposed in the bores, the flange
arranged to mate with a complementary connector disposed on an end
of a conduit through which the fluid flows.
3. The meter of claim 1 wherein the bores of each fixture are arranged
substantially parallel to each other.
4. The meter of claim 1 wherein the tubes and fixtures are each
formed from a weldable, non-reactive material.
5. The meter of claim 4 wherein the material is stainless steel.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to mass flow meters of the Coriolis-type
and, more particularly, to such a mass flow meter for use in sanitary
2. Description of the Prior Art
Coriolis-type mass flow meters are well known in the art and are
used to measure the mass and/or density of a fluid or fluid-like
material. Representative examples of such mass flow meters are U.S.
Pat. Nos. 4852410 and 4756198. Although details of construction
and operation differ somewhat, in general Coriolis-type mass flow
meters utilize a pair of tubes disposed between an inlet and an
outlet connected in line to a pipe carrying a fluid or fluid-like
material (e.g. a slurry) whose mass and/or density is to be measured.
External magnetic drivers are used to vibrate the tubes at a characteristic
frequency. A change in the frequency measured by motion sensors
arranged on the tubes is indicative of the mass flow rate of the
fluid travelling through the tubes.
In their usual arrangement, the tubes are held rigidly fixed at
one end by an inlet fixture having a Y-shaped passage which causes
fluid entering the inlet fixture from an inlet pipe to be split
into two substantially equal streams flowing into the fixed ends
of the tubes. The opposite ends of the two tubes are also rigidly
fixed to an identical outlet fixture having a Y-shaped passage which
causes the streams coming from the two tubes to be recombined and
applied to an outlet pipe. Such an arrangement is shown in U.S.
Pat. No. 4852410 and is used in Schlumberger Industries M brand
mass flow meter upon which U.S. Pat. No. 4852410 is based.
One drawback to the use of such Y-shaped tube fixtures is that
the ends of the tubes must be firmly secured within or to the ends
of the Y-shaped passages formed in the fixtures. Generally, the
tube ends are secured to the Y-shaped passages by means of welding.
This poses several problems. First, this requires that the weld
between the interior end of the tube and the inside of each Y-shaped
passage be made well inside the fixture. This is a particularly
difficult operation when smaller sizes of tubing, e.g. one-half
inch (13 mm). are used. Second, it is difficult to machine and polish
the inside of the Y-shaped passages sufficiently to prevent surface
irregularities from interrupting the smooth flow of fluid through
the passages and from leaving any areas where contaminants may hide.
Finally, the process of creating a weld between the interior of
the tube end and the inside wall of each Y-shaped passage often
results in a rough edge or lip surrounding the tube end at the well
which is also difficult to make smooth and free of places where
contamination may reside.
Such drawbacks are especially significant when a mass flow meter
of the type described above is to be used in a so-called "sanitary"
environment. For example, mass flow meters may be used to measure
the mass and/or density of milk products, food-stuffs, or the like.
Metering equipment of this type must meet various sanitary standards
and regulations such as the "3-A" Sanitary Standard No.
28-01 of the Sanitary Standards Symbol Administration Council. These
standards and regulations require that the metering mechanism be
free of areas or obstructions where foodstuffs or contaminants can
hide, and that the metering mechanism be easily removable from the
fluid flow pipeline to allow for easy cleaning, sanitization, and
SUMMARY OF THE INVENTION
The present invention provides an arrangement enabling a Coriolis-type
mass flow meter of the type shown in U.S. Pat. No. 4852410 to
meet sanitary specifications. In particular, the invention is a
Coriolis-type mass flow meter of the type having an inlet and an
outlet, and at least a pair of tubes disposed between the inlet
and outlet to allow fluid to flow therebetween. Means are provided
for vibrating the tubes and for measuring the frequency of vibration
of the tubes and for deriving therefrom a measure of the mass of
fluid flowing through the tubes. There is further provided an inlet
fixture and an outlet fixture for rigidly holding ends of the pair
of tubes, with the inlet fixture and the outlet fixture being substantially
identical in structure. Each fixture has a pair of separate and
unconnected bores formed therein for receiving the ends of the tubes.
The wall of a bore is in contact with an outer surface of its associated
tube along the entire length of the bore, with each tube being arranged
with its end substantially flush with an end of its associated bore.
Preferably, the tubes and fixtures are formed from a non-reactive
and weldable material, such as stainless steel. The tube ends which
are flush with the ends of the bores in each fixture may be secured
by means of welding between the tube end and bore. The bores of
each fixture may be arranged substantially parallel to each other.
The inlet fixture and outlet fixture may each include an annular
flange formed about each pair of bores in proximity to the ends
of the tubes disposed in the bores. The flange is arranged to mate
with a complementary connector disposed on an end of a conduit or
pipe through which the fluid or fluid-like material flows.
The foregoing arrangement has several advantages over prior-art
Y-shaped inlet and outlet tube fixtures. First, since the ends of
the tube are brought out flush with their respective bores, the
process of welding the tube end to the flush end of the bore takes
place in a readily accessible location. This also means that any
irregularities in the surface of the resulting weld can be easily
filed or ground down to create a smooth area free of discontinuaties
or obstructions which may interrupt the smooth flow of fluid into
or out of the fixture and which will not create an area where contaminants
may hide. This arrangement also eliminates the need to smoothly
machine the inside surface of the bores as is the case with prior-art
tube fixtures having Y-shaped passages since the bores of the present
invention are merely used to locate and secure the ends of the tubes
and do not come into contact with the fluid itself. Finally, the
provision of an annular flange arranged about the fixtures enables
the inlet fixture and outlet fixture to be readily attached or removed
from its associated fluid flow conduit or piping.
It will be appreciated that the arrangement of inlet and outlet
fixtures and tubes of the present invention minimizes areas where
contaminants or foodstuffs may be deposited. Only the flange area
of each fixture and the interior surface of the tubes are actually
in contact with the fluid to be measured. The flange ends of the
fixtures and the tubes themselves may be easily cleaned, sanitized
or sterilized and contain no internal welds or seams where contamination
or foodstuffs may linger even after cleaning.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
These and other features and advantages of the present invention
will be described in the following detailed description of the preferred
embodiment, when taken in conjunction with the accompanying drawing
FIG. 1 shows a typical prior-art Y-shaped tube fixture and flow
FIG. 2 is a side plan view of a Coriolis-type mass flow meter having
inlet and outlet fixtures constructed in accordance with the principles
of the present invention;
FIG. 3 is a top cross-sectional view of the tubes and fixtures
shown in FIG. 2;
FIG. 4 is an end plan view of the tubes and fixtures shown in FIG.
FIG. 5 is a detail perspective view of one of the fixtures shown
in FIGS. 2 and 3; and
FIG. 6 is a detail cross-sectional view of a portion of one of
the fixtures of FIG. 2 taken along lines 6--6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a cross-sectional view of a typical prior-art Y-shaped
tube fixture and flow divider, of the type shown in U.S. Pat No.
4756198 and incorporated in Schlumberger Industries, Inc.'s M
brand mass flow meter upon which U.S. Pat. No. 4852410 is based.
Inlet and outlet fixtures 1 are identical and have formed therein
a Y-shaped set of internal passages 3 5 and 7 with passages 3
and 5 being the arms of the "Y" and common passage 7 being
the base of the "Y". The portion of fixture 1 containing
common passage 7 may further include a flange 9 for connecting to
an external pipe or conduit. The ends of passages 3 and 5 are adapted
to receive a pair of tubes 11 and 13.
In order to minimize disturbances in the transition between tube
11 and 13 and passages 3 and 5 the interior diameter of tube 11
and 13 is normally dimensioned to be the same as the diameter of
interior passages 3 and 5.
In order to be able to secure tubes 11 and 13 to the ends of passages
3 and 5 of fixture 1 there are provided a pair of mounting collars
15 and 17 having an interior diameter dimensioned to snugly fit
around the exterior dimensions of tubes 11 and 13. Mounting collars
15 and 17 are then secured to fixture 1 e.g. by welding external
welds 19 and 21. Tubes 11 and 13 are then inserted into collars
15 and 17 and secured to the collars by welds 23 and 25 respectively.
While the foregoing arrangement or the variation shown in U.S.
Pat. No. 4756198 is adequate for ordinary use, it is difficult
to adapt this arrangement to meet the requirements for sanitary
applications. This is because the joint between the ends of tubes
11 and 13 and the interior of passages 3 and 5 is not seamless.
The area where the interior surface of tubes 11 and 13 adjoins the
interior surfaces of passages 3 and 5 can cause disturbances in
fluid flow through passages 3 and 5 and tubes 11 and 13 unless
it has exactly the same dimensions and degree of smoothness. Furthermore,
this joint can act as a trap for contaminants, making it extremely
difficult to clean fixture 1 to meet the requirements of sanitary
standards. In addition, the Y-shaped passages of fixture 1 are difficult
to machine smooth to minimize interruptions to fluid flow and to
meet sanitary standards. It is also possible to weld the abutting
interior surfaces of tubes 11 and 13 and passages 3 and 5 together
to remove the undesirable interior seam. However, such an interior
weld is difficult to execute due to its location. In addition, any
such weld would need to be smoothed or further polished to ensure
that the interior weld did not itself act as an obstruction to fluid
flow or as a trap for contaminants. This is especially true when
dealing with smaller, e.g. half inch (13 mm). diameter tubing and
FIGS. 2-6 show an improved form of an inlet and outlet fixture
for a mass flow meter which is particularly useful for sanitary
applications. Identical inlet and outlet fixtures 27 and 29 support
the ends of a pair of tubes 31 and 33. The ends of tubes 31 and
33 fit within a pair of bores 35. 37 formed in fixture 27 and bores
39 41 formed in fixture 29. Bores 35. 37 ant 39 41 are substantially
cylindrical in shape and are dimensioned to snugly receive the ends
of tubes 31 and 33 therein. Bores 35. 37 and 39. 41 are separate
and unconnected with each other, with bore 35 having a longitudinal
axis arranged substantially parallel to that of bore 37. Likewise,
the longitudinal axis of bore 39 is arranged substantially parallel
to that of bore 41. The ends of tubes 31 and 33 are brought out
flush with the ends of bores 35 37 and 39. 41.
Tubes 31 and 33 and fixtures 27 and 29 are preferably formed from
a non-reactive, weldable material, such as stainless steel. The
ends of 31 and 33 which are flush with bores 35 37 and 39 41
are secured to fixtures 27 and 29 by means of welding as shown in
more detail in FIGS. 5 and 6. These welds, indicated at 43 45 and
47. 49 are easily performed since they are located at a readily
accessible area on fixtures 27 and 29. This also enables any slight
irregularities in the welds to be easily filed, machined off or
polished. If desired, the areas where tubes 31 and 33 exit through
the opposite ends of bores 35 37 and 39 41 opposite the flush
ends of the tubes may also be welded as indicated by reference numerals
51 53 and 55 57.
Also shown are flanges 59 and 61 disposed about the flush tube
ends of fixtures 27 and 29 respectively. Flanges 59 and 61 are
arranged to mate with complementary connectors 63 and 65 associated
with the conduit or piping 67 and 69 through which a fluid or fluid-like
material which is to be measured by the mass flow meter flows.
Not shown in the drawing figures are means for vibrating tubes
31 and 33 and means for measuring the frequency of vibration of
the tubes and deriving therefrom a measure of the mass flow and/or
density flowing through tubes 31 and 33. Such vibrating means and
measuring and deriving means are shown and discussed in detail in
U.S. Pat. No. 4852410 whose specification is hereby explicitly
incorporated herein by reference. In any event, the vibrating means,
and measuring and deriving means are well-known in the art and do
not constitute a part of the present invention.
The foregoing arrangement results in a tube end fixture having
no interior seams or welds. The only welds in contact with the fluid,
welds 43 45 and 47 49 are readily accessible meaning that these
welds are easy to perform and they can be readily smoothed or polished
to the degree required to meet sanitary standards. Furthermore,
this arrangement enables all exterior areas (e.g. the flanges) and
interior areas (e.g. the tubes) to be easily cleaned or sanitized.
While the present invention has been described in considerable
detail, it is understood that various modifications will occur to
those skilled in the art, therefore, the foregoing detailed description
of the preferred embodiment is not intended to be limitive of the
present invention which is defined by the appended claims.