The flow meter has in a substantially cylindrical inner housing
(1) a helically designed diffuser (4), which imparts a swirl to
the medium flowing through the inner housing. Downstream of the
diffuser there is rotatably mounted a rotor (8), which has blades
(13) extending from its rotational spindle (9) as well as a ring
(14) which connects the blade ends to one another and is coaxial
to the spindle. The rotor (8) is set in rotation by impingement
of the blades (13) by the flowing medium. On the outer circumferential
surface (15) of the ring (11) there is on a circular line a multiplicity
of markings (16) arranged at equal angular intervals from one another.
Through a window (18) in the inner housing (1), a light beam strikes
the outer circumferential surface (15) of the ring (14), provided
with the markings (16). Upon rotation of the rotor (8), the sequence
of markings is transmitted by an optical-fibre cable (20) and sensed
by a sensor (21), so that from the signals received the flow rate
can be determined. The flow meter has the advantage that the medium
to be measured does not have to be transparent as in the application
of the light barrier and that the multiplicity of markings allows
an increase in the measuring accuracy.
1. A flow meter comprising:
a substantially cylindrical housing;
a rotor coaxially mounted for rotation in said housing, said rotor
including curved blades having a full surface area;
a helical diffuser disposed in a passage of the housing coaxially
upstream of said rotor for dividing a flow medium flowing through
the housing into a plurality of streams and generating a swirl so
as to rotate the rotor by impinging the blades;
a ring member disposed coaxially with said rotor and affixed to
and surrounding outer ends of said blades so as to be rotated with
said blades through successive revolutions; and
means for signal generation which interact with the rotor to determine
a flow rate of the medium based upon the revolutions of said ring
2. A flow meter according to claim 1 wherein the ring has markings
circumferentially distributed on an outer circumferential surface
thereof, and the means for signal generation have light-beam focusing
means as well as an optical sensor for the generation of signals
for determining the flow rate.
3. A flow meter according to claim 1 or 2 wherein the blades of
the rotor are axially parallel curved and the ring of full surface
area extends over the width of the blades.
4. A flow meter according to claim 3 wherein the ring and the
blades are designed in one piece.
5. A flow meter according to claim 3 wherein the ring is arranged
symmetrically with respect to the blade width in an axial direction.
6. A flow meter according to claim 2 wherein the outer circumferential
surface of the ring has a multiplicity of color markings arranged
on a circular line at equal angular intervals.
7. A flow meter according to claim 2 wherein the markings are
8. A flow meter according to claim 1 wherein the housing is surrounded
by an outer housing having a lens for focusing a light beam and
having a connection for an optical-fibre cable, which connects the
flow meter to an optical sensor.
9. A method of measuring a flow rate of a medium flowing through
a passage, the passage including a rotor rotatably mounted therein,
the rotor including blades, a ring member being affixed to ends
of the blades, the ring member having markings distributed about
a circumferential surface thereof, said method comprising the steps
directing the flow medium past the rotor so as to rotate the rotor
through successive revolutions;
focusing a light beam on the markings of the ring member;
sensing reflected light pulses produced by the rotating markings
with an optical sensor; and
determining a flow rate based upon an output signal of said optical
The invention relates to a flow meter, and in particular, to a
flow meter having a helical diffuser and a rotor for measuring volumetric
flow of a medium.
A flow meter of the specified type is known, for example, from
European Patent Specification 0228577. In the case of this flow
meter, there is arranged upstream of the rotor, which is disposed
in a flow passage for the medium, a helical diffuser for generating
a swirl in order to impinge on axially parallel extending and circumferentially
bent blades of the rotor which sets the latter in rotation. Each
blade of the rotor has a window designed as an axially parallel
slit. A beam of a light barrier directed at right angles to the
rotor spindle, passes the window. The light source of the light
barrier is arranged on one side and the light receiver being arranged
on the opposite side of the rotor on the housing. This principle
presupposes, however, that the medium of which the flow rate is
to be measured is transparent to enable transmission of the light
beam of the light barrier and thus, restricts its possible applications.
In addition, the number of pulses to be received per rotor revolution
for the measurement when blade windows are to be passed is restricted
to three, due to blade overlapping.
Whereas the known flow meter operates reliably in applications
with relatively great flow rates, at low flow rates it shows that
it is not capable of supplying accurate measuring results.
The present invention is therefore based on the object of providing
an inexpensively producible flow meter which, on account of accurate
measuring results even at the smallest rates, can be used universally.
To achieve this object, the flow meter has a substantially cylindrical
housing and a rotor coaxially mounted for rotation in the housing.
The rotor includes curved blades having a full surface area. A helical
diffuser is disposed in a passage of the housing with the passage
being coaxially upstream of the rotor. The diffuser divides a flow
medium flowing through the housing into a plurality of streams and
generates a swirl so as to rotate the rotor by impinging the blades.
A ring member is affixed to and surrounds outer ends of the blades.
A signal generator is provided which interacts with the rotor to
determine a flow rate of the medium.
The use of a ring on the rotor in combination with the impingement
of the curved blades on their concave side brings about an increase
in the response sensitivity of the same. The cause for this is likely
to be an approximately complete utilization of the kinetic energy
of the flow of which the throughput is to be measured. This takes
place by preventing a radial flow-off in the blade region. In this
case, due to the rigid anchoring of the blades, the ring can also
be used for stiffening the blades at their outer ends. This allows
the blade mass to be reduced without reducing the impinged surface
area. Consequently, the overall mass of the rotor does not increase
due to the mass of the ring.
The ring is expediently designed in one piece together with the
blades and the rotor spindle, which benefits both the stiffness
and the reduction in mass. Moreover, a rotor produced in one piece
allows corresponding assembly costs to be avoided. According to
a preferred further development of the flow meter according to the
invention, the counting or measuring signals are obtained by scanning
the outer surface of the rotor ring, provided with markings. Since
the flow meter consequently does not have to keep a beam path clear
for a light barrier, the form of the rotor is simplified. The universal
applicability of the flow meter is further increased inter alia
by the fact that the medium does not have to be transparent. Apart
from this, virtually any number of signals can be generated per
Further details and advantages emerge from the following description,
in which an embodiment of the flow meter is described in more detail
purely by way of example with reference to the drawings, in which:
FIG. 1 shows a longitudinal section through a flow meter, on a
scale enlarged approximately ten times.
FIG. 2 shows a cross-section through the flow meter along the line
1--1 in FIG. 1.
The flow meter has an inner housing 1 which is of a tubular design,
preferably consists of a plastic material and can be connected at
both ends to hose lines. A liquid medium flows through the inner
housing 1 in the direction of the arrow 2 from right to left. In
the cylindrical passage 3 of the inner housing 1 there is arranged
a diffuser 4 designed as a multi-thread screw or worm. An axial
core 5 from which the threads 6 start, is extended forwards on
the onflow side into a streamlined body 7. This diffuser divides
the inflowing medium up into various part-streams, which thereby
receive a swirling motion and are accelerated.
Arranged downstream of the diffuser 5 is a rotor 8. The rotor spindle
9 is mounted with play on the onflow side in a bore 10 formed in
the core 5 of the diffuser 4. On the other side, the rotor spindle
9 is mounted, likewise with play, in a bore 11 which is formed in
a narrow traverse 12 passing transversely through the passage 3.
Fastened on the rotor spindle 9 in axially parallel position are
three identical blades 13 which are arranged circumferentially distributed
and are curved over their extent about one or more, exclusively
axially parallel axes of curvature. The thin-walled blades 13 have
a full surface area and, in the exemplary embodiment represented,
have an axial extent which remains constant over the radial extent.
The ends of the blades are fastened on a cylindrical ring 14 coaxial
to the rotor spindle 9. The ring 14 represented is of the same width
as that of the blades 13 which corresponds to an advantageous configuration.
However, the axial extent of the ring may be both greater than and
less than that of the blades. Similarly, an axially symmetrical
arrangement of the ring with respect to the blades is not necessary.
An arrangement in which the ring is arranged offset in the axial
direction in such a way that it leaves the blades clear on one side
and projects axially over them to the other side may also be expedient.
In any event, the ring has a full surface area and end faces lying
in parallel radial planes.
The curvature of the rotor blades 13 is designed in such a way
that the latter are impinged on their concavely curved side by the
helical flow formed by the diffuser 5.
In any event, the rotor, comprising rotor spindle 9 blades 13
and ring 14 is expediently designed in one piece. Even with the
thinnest-wall design of the blades and of the ring, this produces
high strength and dimensional stability with the least rotor mass.
At the same time, such a one-piece rotor can be produced with a
relatively simple mould in an injection process, for example from
plastic material, if the blades are curved only about axes which
run parallel to the spindle of the rotor.
However, it is essential for the flow meter according to the invention,
or the dynamic behavior thereof, that the configuration and/or arrangement
of the ring 14 on the rotor enforces a flowing away of the medium
in approximately axial direction and prevents any radial flowing
away, in particular at the radially outer ends of the blades 13.
Since clearance losses between rotor and surrounding passage are
consequently already eliminated to a great extent, the flow energy
of the medium is retained completely for the impingement of the
blades. It has been shown that the impingement of the blades on
the concave side, together with the ring, significantly increases
the response sensitivity and plays a part in increasing the measuring
accuracy, in particular at lower flow rates.
The clearance between rotor-ring 14 and the inner wall of the passage,
which can be seen in the drawing, is of course not shown to scale
in its radial dimension and in reality, is very narrow. By means
of an inwardly protruding circumferential shoulder in the passage,
which is arranged before or, as shown, after the ring (considered
in the direction of flow), radial flowing away of the medium past
the rotor is avoided to the greatest extent.
If the ring 14 extends in particular less far downstream than the
blades 13 the inside diameter of the passage must be approximately
the same as the inside diameter of the ring in order to avoid any
radial flowing away of the medium.
On the outer circumferential surface 15 of the ring 14 there are
formed or arranged a multiplicity of markings 16 on a circular line
at equal angular intervals from one another. The markings are preferably
depressions worked into the surface during production of the ring;
color markings are also possible. The markings 16 are sensed when
the rotor 8 is rotating by a light beam 17 directed against the
outer surface 15 of the ring 14 for example by a laser beam which
passes from outside through a window 18 in the inner housing 1 to
strike the outer circumferential surface 15 of the ring 14 in the
region of the markings 16 present there. When the rotor 8 is rotating,
the light beam thus alternately strikes a marking 16 and the annular
surface between the markings, and the light returned with varying
intensity is focused by a lens 19 arranged externally in front of
the window 18 and fed via a fiber optic cable 20 to a sensor 21.
From the signals thus obtained, the flow rate per unit of time can
be determined. The fiber optic cable 20 is connected to an outside
housing 22 which can be screwed on and in which the lens 19 is
also exchangeably arranged.
Devices for the emitting of a light radiator and for the optical
sensing of the reflected light pulses are known. For example, the
fiber optic cable 20 may have regions which are separate from one
another in the longitudinal direction, one of which conducts the
light beam directed against the rotor outer surface 15 and passes
the returned light pulses through the other region to the optical
The advantage of this device is that, for the generation of signals,
it is not dependent on the interruption of a light path and consequently
allows a closed ring without windows, completely covering over the
blades. Obviously, this device does not allow the generation of
a number of signals per rotor revolution corresponding to the number
of blades each having a window, but the generation of a multiplicity
of signals corresponding to the number of markings present on the
circumference of the ring. The significantly increased signal sequence
allows the accuracy of the flow meter to be increased in certain
applications. It is likewise of advantage that the flow meter described
is also suitable for measuring the flow rate of any non-transparent
Together with the great number of signals per revolution, the increased
response sensitivity of the low-mass rotor produces extremely accurate
measuring results in all areas of application.