Abstrict A Coriolis-force mass flow meter is proposed, which is clamped
at one side in a rigid mounting, has a tubular loop through which
a test medium is flowing and which, relative to the mounting, is
capable of oscillating itself about a particular axis of oscillation
and can be given a rotary oscillation about a specified axis of
rotation by an exciter system. In the state of the art, the axis
of oscillation and the axis of rotation essentially coincide. In
contrast to this, the special feature of the inventive flow meter
consists therein that said axes have an angle that is significantly
different from 0.degree., the axis of rotation having a directional
component parallel to the plane of the tubular loop. In this way,
a significant improvement in respect to signal generation is achieved.
In the drawing, (1) refers to the tubular loop, (2) to the loop
mounting, (3) to the support of the loop mounting, (5) to the exciter
system, SA to the axis about which tubular loop (1) is capable of
oscillating, and DA to the axis of the excited rotary oscillation.
Claims I claim:
1. Mass flow meter with at least one tubular loop, through which
a test medium is flowing and which is clamped at one side into a
rigid loop mounting, forms at least a half turn and can be elastically
deflected relative to the loop mounting transversely to the plane
of the loop mounting about an axis of oscillation, that is defined
by the clamping, moreover with an exciter system, which imposes
a primary oscillation about a specified axis of rotation on the
tubular loop in operation, the oscillatory motion, in conjunction
with the mass flow through the loop, giving rise to Coriolis forces
in this loop, which act on the loop in proportion to the flow, and
with a device for measuring the action that is proportional to the
flow, the tubular loop consisting of two lateral arms extending
at opposite distances from the loop mounting as well as one cross
arm connecting these lateral arms at a distance from the mounting,
the axis of rotation (DA) intersecting or crossing the axis of oscillation
(SA) at an angle significantly different from 0.degree. and moreover
having a directional component parallel to the plane of the loop
and the axis of rotation intersecting the cross arm of the tubular
loop or crossing it at a minimum distance, wherein there is a device
for suppressing deflections (7) of the cross arm (1c) of the tubular
loop (1 1') at the point of intersection with the axis of rotation
(DA) by generating a counterforce to compensate for the respective
deflection force, the measuring device measuring the magnitude of
the counterforce or a physical quantity that gives rise to this
counterforce.
2. Mass flow meter as defined in claim 1 wherein the axis of rotation
(DA) crosses the axis of oscillation at an angle (a) of about 90.degree.
or at a minimum distance.
3. Mass flow meter as defined in claim 1 wherein the loop mounting
(2 2') is supported in a support (3) so that it can rotate about
the axis of rotation (DA) and wherein the exciter system (5) gives
the loop mounting (2 2') and, over this, the tubular loop (1 1')
a rotary oscillation about the axis of rotation (DA).
4. Mass flow meter as defined in claim 1 wherein the side arms
(1a, 1b) of the tubular loop (1 1') run essentially parallel to
each other and extend essentially perpendicular to the axis of oscillation
(SA) and the cross arm (1c) is essentially perpendicular to the
side arms (1a, 1b).
5. Mass flow meter as defined by claim 4 wherein the new axis
or rotation (DA) intersects or crosses the cross arm (1c) in the
center.
6. Mass flow meter as defined in claim 1 wherein the inertial forces,
caused by the oscillatory motion of the loop mounting (2) and the
tubular loop (1), and acting on the support (3) of the loop mounting
(2), are compensated for by mass balancing system (15 16) exerting
a counteraction on this support (3) and oscillating with the same
frequency but opposite phase.
7. Mass flow meter as defined in claim 6 wherein the new mass
balancing system (16) comprises an identical repetition of the tubular
loop (1) with the associated loop mounting (2).
8. Mass flow meter as defined in claim 7 wherein the new test
medium flows through the two tubular loops (1 1') in the same direction,
so that the measuring device (8 9) measures the sum of the two
individual flows.
9. Mass flow meter as defined in claims 7 wherein the new test
medium flows through the two tubular loops (1 1') in the opposite
direction, so that the measuring device (8 9) measures the difference
between the two flows.
10. Mass flow meter as defined in claim 6 wherein the support (3)
of the loop mounting (2 2') is spring-mounted at the housing of
the flow meter.
11. Mass flow meter as defined in claim 6 wherein the measuring
device (8 9) is arranged so as to be stationary with respect to
the support (3) of the loop mounting (2 2').
12. Mass flow meter as defined in claim 1 wherein a second measurement
device (18) is provided, which measures the motion of the loop mounting
(2 2') relative to the support (3) or relative to the housing of
the mass flow meter and whose signal is used to compensate for a
possible zero point error due to external influences.
13. Mass flow meter with at least one tubular loop, through which
a test medium is flowing and which is clamped at one side into a
rigid loop mounting, forms at least a half turn and can be elastically
deflected relative to the loop mounting transversely to the plane
of the loop mounting about an axis of oscillation, that is defined
by the clamping, moreover with an exciter system, which imposes
a primary oscillation about a specified axis of rotation on the
tubular loop in operation, the oscillatory motion, in conjunction
with the mass flow through the loop, giving rise to Coriolis forces
in this loop, which act on the loop in proportion to the flow, and
with a device for measuring the action that is proportional to the
flow, the tubular loop consisting of two lateral arms extending
at opposite distances from the loop mounting as well as one cross
arm connecting these lateral arms at a distance from the mounting,
the axis of rotation (DA) intersecting or crosssing the axis of
oscillation (SA) at an angle significantly different from 0.degree.
and moreover having a directional component parallel to the plane
of the loop and the axis of rotation intersecting the cross arm
of the tubular loop or crossing it at a minimum distance, wherein
the measuring device (8) measures the mutual phase position of the
oscillation, which the side arms (1a, 1b) of the tubular loop (1
1') execute at a distance from the loop mounting (2), preferably
in the vicinity of the cross arm (1c) of the tubular loop (1 1').
14. Mass flow meter with at least one tubular loop, through which
a test medium is flowing and which is clamped at one side into a
rigid loop mounting, forms at least a half turn and can be elastically
deflected relative to the loop mounting transversely to the plane
of the loop mounting about an axis of oscillation, that is defined
by the clamping, moreover with an exciter system, which imposes
a primary oscillation about a specified axis of rotation on the
tubular loop in operation, the oscillatory motion, in conjunction
with the mass flow through the loop, giving rise to Coriolis forces
in this loop, which act on the loop in proportion to the flow, and
with a device for measuring the action that is proportional to the
flow, the tubular loop consisting of two lateral arms extending
at opposite distances from the loop mounting as well as one cross
arm connecting these lateral arms at a distance from the mounting,
the axis of rotation (DA) intersecting or crossing the axis of oscillation
(SA) at an angle significantly different from 0.degree. and moreover
having a directional component parallel to the plane of the loop
and the axis of rotation intersecting the cross arm of the tubular
loop or crossing it at a minimum disstance, wherein the measuring
device (9) measures the flow-proportional deflection (7) of the
cross arm (1c) of the tubular loop (1) at the point of intersection
with the axis of rotation (DA).
Description SUMMARY OF INVENTION
The invention relates to mass flow meter.
Known mass flow meters have been formed with a tubular loop of
a U shape with parallel side arms clamped at one end to a loop mounting.
A cross arm connects the side arms. The tubular loop is excited
by a driving system into a primary oscillation which is a rotary
oscillation about the axis of oscillation, and the axis of rotation
and axis of oscillation coincide. It is an object of the invention
to provide a mass flow meter of the type formed with the U shaped
tubular loop as above discussed, which is capable of supplying significantly
larger measuring signals than previously available with mass flow
meters of this type, and permitting reliable measurement of significantly
smaller flows. In the improved mass flow meter, the tubular loop
and, with it, the part of the tubular loop, which is practically
always present and corresponds to the cross arm of the known flow
meters, is excited by the exciter system to a--primary--rotary oscillation
about the axis of rotation. This primary, rotary oscillation, in
conjunction with the mass flow rate, gives rise in said part of
the tubular loop to Coriolis forces, which result in translatory
deflection of this tubular loop part, which is proportional to the
flow, displaced by 90.degree. relative to the exciting oscillation
and superimposed on the primary rotary oscillation. The translatory
deflection manifests itself as an oscillation of said tubular loop
part about the axis of oscillation of the tubular loop, and the
flexural resistance of the tubular loop about the axis of oscillation
is significantly smaller than the flexural resistance about the
axis of the secondary oscillation, exhibited by the tubular loop
of the known flow meters. Thus, a significantly larger measuring
signal is obtained than attained in flow meters having dimensions
of the same order of magnitude permitting the use of thicker tubes
for the same measuring range.
BRIEF DESCRIPTION OF DRAWINGS
The invention is explained in greater detail below by means of
examples of the operation shown in the drawing.
FIG. 1 shows the mass flow meter in a simplified representation
in perspective view for explaining the basic principle;
FIG. 2 shows, as a function of time, the course and the mutual
phase position of the oscillations, executed by the side arms or
the cross arm of the tubular loop of the flow meter of FIG. 1;
FIG. 3 is a first practical design of the inventive mass flow meter
in schematic representation in perspective view;
FIG. 4 is a second practical design in schematic representation
and perspective view.
DETAILED DESCRIPTION
The flow meter of FIG. 1 has a tubular loop 1 one side of which
is clamped into a rigid loop mounting 2. The flow meter can be deflected
elastically relative to the loop mounting 2 and transversely to
its plane about an axis of oscillation SA that is defined by the
clamping. The tubular loop 1 forms a half turn and comprises two
side arms 1a and 1b, which extend at a spaced distance from each
other from the loop mounting 2 and one cross arm 1c, which connects
these at a distance from the mounting 2.
The tube mounting 2 is mounted, so that it can rotate about the
axis of rotation DA, in a support 3 that, like the axis of rotation
DA, lies in the plane of the tubular loop. The axis of rotation
DA extends parallel to side arms 1a and 1b of tubular loop 1 forms
an angle of about 90.degree. with the axis of oscillation SA and
intersects cross arm 1c of tubular loop 1 essentially in the center.
The test medium, usually a fluid, is supplied to the tubular loop
1 at one clamped end and emerges from this loop at the other clamped
end, as indicated by arrows 4 in FIG. 1. In so doing, it flows,
in order, through side arm 1a, cross arm 1c and side arm 1b.
Immediately next to the loop mounting 2 which consists of a magnetic
material here, there is arranged an electromagnetic exciter system
5 which displaces the loop mounting 2 and, by way of this, the
tubular loop 1 into a primary rotary oscillation about the axis
of rotation DA. As long as the test medium is at rrest in tubular
loop 1 that is, as long as the flow has the value of zero, side
arms 1a execute essentially sinoidal oscillations at the ends adjacent
to cross arm 1c. These oscillations are shown in FIG. 2 (a and
b), by the unbroken curves, which are mutually displaced by 180.degree.
, that is, their phases are opposite. In FIG. 1 these oscillations
are indicated by arrows 25 and 26 the unbroken arrows on the one
hand and the broken arrows forming pairs that belong together in
respect to time.
When the test medium flows through tubular loop 1 it moves in
cross arm 1c first of all towards the axis of rotation DA and then
away from it. As a result, Coriolis forces arise in cross arm 1c
under the influence of the rotary oscillations taking place about
the axis of rotation DA. The magnitude of the Coriolis forces is
proportional to the flow and these forces endeavor to deflect arm
1c about the axis of oscillation SA, the direction of the deflection
changing periodically with rotary oscillation of the tubular loop
1 about the axis of rotation DA. This translatory deflection of
cross arm 1c, which manifests itself at tubular loop 1 as a rotary
oscillation about the axis of oscillation SA with an amplitude proportional
to the flow, is shifted by 90.degree. relative to the primary rotary
oscillation of the tubular loop 1 about the axis of rotation DA,
the oscillation that is caused by the exciter system 5. This is
shown in section c) of FIG. 2. In FIG. 1 this oscillation is indicated
by arrows 7.
The oscillation from the Coriolis force, which is proportional
to the flow, is superimposed on the fundamental oscillations, shown
as unbroken lines in FIGS. 2a and 2b, in the manner indicated by
a broken curve and leads to a phase displacement .DELTA..phi. between
the resulting oscillations, which the side arms 1a and 1b carry
out at the ends adjacent to the cross arm, the phase displacement
being exactly proportional to the Coriolis force and therefore to
the flow.
About the axis of oscillation SA, about which the Coriolis forces
in the cross arm 1c of tubular loop 1 bring about the secondary
osscillation, tubular loop has basically a slight flexural resistance,
which naturally depends on the nature of the tube, so that even
thick tubes can supply an unambiguously measurable deflection, as
indicated by arrow 7 for relatively slight flows or correspondingly
thinner tubes can still indicate extremely small flows with an unambiguously
measurable deflection.
The deflection of tube 1 is measurable in various ways. FIG. 1f
shows two different measuring devices, which are suitable for this
purpose. One of these devices is labelled 8 and measures the phase
displacement .DELTA..phi. between the oscillations carried out by
those ends of side arms 1a and 1b of tubular loop 1 which are adjacent
to cross arm 1c. The second, alternatively usable measuring device
is labelled 9 and measures the magnitude of the deflection of cross
arm 1c, as indicated by arrow 7 at the point of intersection of
this arm with the axis of rotation DA, that is, it measures the
amplitude of the oscillation as shown in FIG. 2c. A signal proportional
to the flow is generated by an electronic device 10 from the displacement
of the phase or from the amplitude of the deflection and is indicated
by indicating instrument 11.
A different possibility of measuring the flow through tubular loop
1 on the basis of the Coriolis forces arising in cross arm 1c, which
is subject to the primary rotary oscillations, consists of providing
a device, which counteracts the deflections of the cross arm at
the point of intersection with the axis of rotation DA by generating
a counterforce that compensates for the respective deflection force
in such a manner, that the deflections are practically prevented,
the measuring device then measuring the magnitude of the counterforce
or the physical quantity that produces the counterforce, such as
the current when the counterforce is generated electromagnetically.
Without special, additional facilities, a flow meter, constructed
as shown in FIG. 1 would exert considerable inertial forces on
the housing, in which the individual parts of the flow meter are
arranged and held. Versions of the flow meter, designed basically
as in FIG. 1 but in each case with facilities to prevent this, are
shown in FIGS. 3 and 4.
In the two constructions of FIG. 3 on the one hand and FIG. 4 on
the other, a balancing of masses is provided. The inertial forces,
caused by the oscillatory motion of the loop mounting 2 and the
tubular loop 1 and acting on the support 3 of the loop mounting
2 are compensated for by a mass balancing system 15 or 16 which
oscillates with the same frequency but the opposite phase and exerts
a counter-action on this support 3. In the construction of FIG.
3 this mass balancing system is a beam 15 rotatably supported,
like mounting 2 at support 3 and displaced by the exciter system
5 to this oscillation of opposite phase with a flywheel effect about
its axis of rotation that is parallel to the axis of rotation DA,
which compensates for the flywheel effect of the oscillating flow-metering
part. In the construction of FIG. 4 these facilities consists of
an identical repetition of the tubular loop 1 with the associated
loop mounting 2. In the construction of FIG. 4 the phase of the
oscillation of the repeated tubular loop 1' with the associated
mounting 2' is also opposite to that of tubular loop 1 and its mounting
2.
On account of the two tubular loops 1 and 1', present in the construction
of FIG. 4 and identical with one another, this construction also
offers the possibility, provided that the measuring device 8 or
9 is designed appropriately, of measuring the sum or the difference
of the individual through-puts through tubular loop 1 on the one
hand and through tubular loop 1' on the other. For example, owing
to the fact that a particular test medium is sent in series through
tubular loops 1 and 1', the measurement signal is doubled when the
sum is measured. An example of the difference measurement is the
supply of fuel to an engine through one tubular loop and the discharge
of excess fuel, not consumed by the engine, through the other tubular
tube. By these means the fuel, consumed by the engine, is indicated
as the result of the difference measurement.
For all of the embodiments illustrated above, the support 3 the
exciter system 5 and the measuring devices 8 and 9 can be connected
rigidly with the housing of the flow meter and, in so doing, can
also be coupled rigidly to each other.
For the specific embodiments described however, the support 3 for
the loop mounting can also be spring mounted on the housing of the
flow meter. The spring mounting has the effect of shielding the
measuring system from vibrations of the housing coming from the
outside or from other external influences. In the latter case, it
is advisable to couple the exciter system 5 and the measuring devices
8 and 9 rigidly with the loop support 2 or the loop supports 2 and
2' and not with the housing.
FIG. 4 also shows yet a second measuring device 18 which functions
much like measuring device 8 but, contrary to the latter, measures
the motion of the loop mounting 2 and/or 2' relative to the housing
of the mass flow meter and the signal of which can be used to compensate
for possible zero-point errors due to external influences. In the
version of FIG. 4 the compensating signal is generated in an electronic
device 19 and superimposed compensatingly on the signal from electronic
device 10. In this manner, interference with the measuring system,
originating from the housing of the flow meter, can be eliminated
practically completely.
The measuring system 18 is preferably connected rigidly with the
housing of the flow meter.
The preceding specifications and the attached drawing are an account
of the best means known at the present time of carrying out the
invention. |