Abstrict A mass flow meter for flowing media with equipment for determining
the coriolis force consists of a helicoidally bent measuring tube
provided with two tube loops whose inflow and outflow ends are fastened
to a massive cast block and between whose oppositely pivotable tube
loops are arranged an oscillator and two sensors measuring the torsional
oscillations. For a more compact stiffening and an improved clamping
of the measuring tube at the cast block, the two tube loops are
in each case ovally bent in one plane, extend approximately parallel
to one another and are provided on one longitudinal side in each
case with two tube sections lying opposite to one another in an
alignment line (x.sub.1 --x.sub.1 or x.sub.2 --x.sub.2). Of these
sections, two are crosswise connected through a central tube part
extending between the two loops and the two other tube sections
are joined to the tube inflow and outflow ends which extend in opposite
directions in a curved shape between the two tube loops and which
run coaxially to the longitudinal sides to the outside. The tube
loops are clamped and welded to the cast block in the area of these
four tube sections.
Claims What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A mass flow meter for flowing media with equipment for determination
of the coriolis force, comprising a helicoidally bent measuring
tube (1) provided with two tube loops (23), whose inflow and outflow
ends (56) are affixed to a block (13) and between which tube loops
(23) are arranged an oscillator (17) and two sensors (18), characterized
in that, the two tube loops (23) are each ovally bent in one plane,
and the loops extend approximately parallel to one another and each
loop is provided with two tube sections (9 10 or 11 12) lying
opposite to one another in an alignment line (x.sub.1 --x.sub.1
or x.sub.2 --x.sub.2) of which two sections (10 11) are crosswise
connected through a curved central tube section (7) that extends
between the loops and the two other tube sections (9 12) join to
the tube inflow and outflow ends (5 6), which extends in opposite
directions in a curved shape between the two tube loops (2 3) and
which extend along substantially the same axis beyond the loops
and that the tube loops (2 3) are anchored to the block 13 in the
area of the four tube sections (9 to 12).
2. The mass flow meter according to claim 1 characterized in that,
the measuring tube (1) consists of two uniform, generally hook-like
bent tube parts (4), which extend from the tube inflow and outflow
ends (5 6) up to the middle of the respective tube loop (2 3)
and to which is connected by two connections (8) the central tube
section (7).
3. The mass flow meter according to claim 2 characterized in that,
the two connections (8) are orbital welding seams each of which
is covered by a ring (16) welded onto the measuring tube (1), to
which ring is fastened the oscillator (17).
4. The mass flow meter according to any one of the claims 1 to
3 characterized in that, the block (13) consists of a base plate
(14) lying within the oval tube loops (2 3) and the base plate
(14) intersecting their planes and a cover plate (15) which has
half shells (21 22) enclosing the measuring tube (1) at the four
tube sections (9 to 12) and which are welded to these tube sections
(9 to 12) as well as to one another.
5. The mass flow meter according to claim 4 characterized in that,
the base plate (14) is provided with support webs (22) an half shells
(24) and is welded together with them.
Description The invention relates to a mass flow meter for flowing media with
equipment for determination of the coriolis force, which consists
of a helicoidally-bent measuring tube, provided with two tube loops,
whose inflow and outflow ends are affixed to a massive cast block
and between whose opposedly pivotable tube loops are arranged an
oscillator and two sensors measuring torsional oscillations of the
loops.
BACKGROUND OF THE INVENTION
A mass flow meter of this general type is known, for example, from
the WO No. 85/05677. In that prior meter design, the measuring tube
(shown in FIG. 4 of that publication) consists of a uniformly bent
tube-piece which is helicoidally bent so that the two tube loops
extend in a spiral path. The inflow and outflow ends of the tube
are guided from the outside tube windings tangentially in opposite
directions and are bent outside of the tube loops into a joint axle
center where also takes place the mounting or clamping of the tubes
on bearing blocks. This fastening results, to be sure, in a relatively
favorable, almost exclusively torsional, stress at the two clamping
sites. However, the great distance between the clamping sites requires
a considerable mechanical expenditure for a stiffening device that
exludes as much as possible external vibration effects. Such mechanical
stiffening devices also require much space.
European Patent Application No. 86 200 575.8 describes a mass flow
meter in which two ovally-bent tube loops, arranged approximately
parallel to one another, as well as an inflow and outflow tube are
welded to a connecting block provided with flow channels. This construction
has, however, the drawback that the measuring tube is subdivided
into four tube sections which have to be welded to the connecting
block in an involved manner. These welding connections of the bent
tube loops are weakened by the deformation forces arising upon oscillation
of the tubes; indeed, in some cases, the connections can be destroyed.
Furthermore, cracks or grooves caused by the welding can exclude
that type of flow meter from certain application fields, e.g. for
the food industry.
SUMMARY OF THE INVENTION
In contrast, this invention has the object to stiffen a mass flow
meter with a continuous measuring tube of the generic type in a
compact manner and to clamp-in the measuring tube at sites that
are favorable for the vibrations of interest. This objective is
achieved by the invention in that the two tube loops of the flow
meter are each always ovally bent in one plane, they extend approximately
parallel to one another and they are always provided on a longitudinal
side with two tube sections each lying opposite to one another in
alignment. Also, of the four tube sections, two tube sections are
connected crosswise by a curved central tube section or part which
extends between the two loops, and the two other tube sections are
joined to the inflow and outflow ends of the tube. Still further,
these ends are guided in the shape of a curve in two opposite directions
to the outside between the two tube loops and coaxially to the longitudinal
sides, and the tube loops are clamped in a cast block and welded-on
in the area of these four tube sections.
This new design of the measuring tube to pass through the flow
meter without any interruption produces a definite advantage in
that the meter is especially compact. Also, the two tube loops have
a particularly favorable form for the generation of mechanical oscillations
and the measurement of the twistings caused by coriolis forces.
Further, since the tube loops are clamped and welded to continuous
sections of the measuring tube there are avoided the above-described
destructive forces on the welding seams. Finally, the measuring
tube of the present flow meter is so favorably bent that the central
tube section which connects the two tube loops and the deflected
tube sections which lead to the inflow and outflow ends of the tube
lie within the space encompassed by the two tube loops.
A particularly favorable assemblage of the equipment can be achieved
in that the measuring tube may consist of two uniform, generally
hook-shaped bent tube parts which extend from the inflow and outflow
ends of the tube up to the center of the pivotable longitudinal
side of the respective tube loop and to which is welded the central
tube section. This construction permits, for the first time, the
relatively easy manufacture and installation of a measuring tube
which is complicated, yet still compact in its design. For manufacture,
there are required only three tube parts, of which two tube parts
are identical. These three tube parts are connected to form a continuous
uniform measuring tube by orbital welding which can produce gap-free
welding seams. The two orbital weld seams are favorably located
at sites on the measuring tube at which arises the lowest mechanical
strain, but which are also symmetrical to the clamping sites. For
protection, the two orbital welding seams may also be covered permanently
by a ring welded to the measuring tube and to which can be affixed
the oscillator component of the flow meter.
The cast block which serves for stiffening and clamping consists
preferably of a base plate, which lies within the oval tube loops
and intersects their planes, and a cover plate which has half shells
enclosing the measuring tube at the four tube sections, and which
are welded to these tube sections, as well as to one another. This
design allows a simple mounting of the equipment. For this, the
cast block is inserted in the measuring tube and positioned so that
the tube sections lie in the half shells. Then, the cover plate
is laid on and welded in place. As support for the inflow and outflow
ends of the tube, the base plate is provided with correspondingly
arranged supporting webs and half shells and is welded to tube ends.
After such assembly, the flow meter with its inflow and outflow
ends, which ends may be provided, for example, with mounting flanges,
is ready to be installed into a pipe line through which flows the
medium that is to be measured.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of the invention is illustrated in the drawing
in an exemplified embodiment, wherein:
FIG. 1 is the measuring tube of a mass flow meter shown in perspective
and diagrammatically;
FIG. 2 is a mass flow meter shown in a lateral view;
FIG. 3 is the FIG. 2 flow meter without its casing shown in a central
longitudinal section;
FIG. 4 is the FIG. 2 flow meter viewed from the front;
FIG. 5 is the FIG. 2 flow meter showing a top view of the measuring
tube and of the cast block, without the cover plate;
FIG. 6 shows the bottom surface of a cover plate for the cast block
depicted in FIG. 5; and
FIG. 7 shows a section of the FIG. 2 flow meter in a view from
the bottom, with the oscillator and the sensors.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The measuring tube 1 shown in FIG. 1 in a simplified manner, consists
of a continuous uniform tube usually made of a corrosive-resistant
material, e.g. stainless steel, through which flows the medium which
is to be measured. The tube is helicoidally bent so that there are
formed two tube loops 2 and 3 which are always ovally bent in a
parallel plane/s and which are spaced apart approximately parallel
to one another (See also FIG. 4).
As the measuring tube 1 presents sort of a knot, it is assembled
out of three tube parts which are gap-free-welded at their joint
abutments according to the so-called butt-weld-orbital-method to
form the continuous uniform measuring tube 1. The three tube parts
consist of two identical, hook-like bent tube parts 4. One of these,
a frontal hook-like bent tube part 4 shown in FIG. 4 forms the
inflow end 5 of the measuring tube 1 and extends over the right
deflection by 180 degrees up to the center of the lower longitudinal
side of the frontal tube loop 2; the other of these, a rear hook-like
bent tube part 4 forms, in like manner, the outflow end 6 of tube
1 and extends over the left deflection by 180 degrees up to the
center of the lower longitudinal side of the rear tube loop 3. The
associated third tube part 7 is shaped generally like a non-planar
letter C i.e. a twisted C, and, on the one hand, forms the other
half of the respective tube loop 2 or 3 and, on the other hand,
connects cross-wise both tube loops 2 and 3.
The welding-together of the three tube parts 4 7 and 4 is done
at two lower joint abutments where the two orbital weld seams 8
are indicated in FIG. 1. From FIG. 1 is seen also that the middle
portion of the central tube part 7 lies at the same height as the
tube sections 9 to 12 proceeding at the top longitudinal sides
of the tube loops 2 and 3 along the alignment lines x.sub.1 --x.sub.1
or x.sub.2 --x.sub.2. The tube inflow and outflow ends 5 6 on
the other hand, are bent in opposite directions obliquely inward
into the space between the two tube loops 23 and they extend from
there between both tube loops 23 out beyond the front end of the
measuring tube 1. The tube segments 9 10 or 11 12 lying opposite
to one another in the alignment lines x.sub.1 --x.sub.1 or x.sub.2
--x.sub.2 comprise the clamp-in sites at which the measuring tube
1 is clamped and fastened in a cast block 13 as shown in FIG. 2.
FIG. 2 shows that the tube sections 9 10 extend out at the head
of the cast block 13 and run downward around the cast block 13 and
form thereby the pivotal oval tube loop 2. Approximately parallel
thereto lies the other identically-designed tube loop 3 (see FIGS.
4 and 5).
The cast block 13 comprises a base plate 14 and a cover plate 15
both of these parts being massive cast pieces. FIG. 2 shows further
that the two orbital weld seams 8 are each covered by a welded-on
ring 16 which also serves as a fastening member for a magnetic oscillator
17. The oscillator is arranged between the two tube loops 2 3 and
sets the loops into opposite oscillations (see FIGS. 4 and 7). FIG.
2 in connection with FIG. 7 shows also two sensors 18 which are
arranged at the sides between the tube loops 23 and which pick
up the torsions of the tube loops 2 3 caused by coriolis forces.
Finally, as shown in FIGS. 2 and 4 the mass flow meter comprising
the measuring tube 1 and the cast block 13 is equipped with a casing
19 consisting of two half shells.
For the clamping and bracing of the measuring tube 1 at the cast
block 13 the base plate 14 and the cover plate 15 is provided with
suitable bearing parts. From FIGS. 3 to 5 it can be seen that the
base plate 14 is provided with sidewalls 26 between which are provided
for support of the aforementioned tube sections 9 to 12 two support
webs 20 which have half shells 21 into which fits, in each case,
a tube section 9 to 12. In a corresponding manner also, the cover
plate 15 shown in FIG. 6 is provided with half shells 22 so that
tube sections 9 to 12 are enclosed and clamped at their circumferences
by the half shells 21 22. For this purpose, the tube sections 9
to 12 are welded to the half shells 21 22. Likewise, the cover
plate 15 is welded to the box-shaped upper rim of the base plate
14. The two supporting webs 20 have cutouts 27 through project the
inflow or outflow end 5 or 6 of the tube. The course of the central
tube part 7 is indicated in FIG. 6 by the associated centerline
25. Further, there are cast onto the base plate 14 supporting webs
23 provided with half shells 24 upon which rest and are welded-on
the tube inflow and outflow ends 56. |