Coriolis-type mass flow meter for sanitary use

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.

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 environments. 
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. 
4,852,410 and 4,756,198. 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. 4,852,410 and is used in Schlumberger Industries M brand 
mass flow meter upon which U.S. Pat. No. 4,852,410 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 
inspection. 
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. 4,852,410 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.

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. 4,756,198 and 
incorporated in Schlumberger Industries, Inc.'s M brand mass flow meter 
upon which U.S. Pat. No. 4,852,410 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. 
4,756,198 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 fixture passages. 
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. 4,852,410 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.