A turbine type flow meter incorporating an auxiliary turbine ahead
of the main turbine, the auxiliary turbine rotating in the opposite
direction from that of the main turbine and serving as a flow conditioner,
thereby extending the effective range of the flow meter to lower
rates of flow.
What is claimed is:
1. A turbine type flow meter comprising:
a housing with an inlet port and an outlet port at opposite ends
of a longitudinal cylindrical opening;
a shaft centrally supported within said cylindrical opening along
the axis thereof;
first and second rotors mounted on said shaft;
a pickoff coil mounted on said housing and excited by an a-c signal
at a given carrier frequency;
said inlet port and said outlet port being fashioned to facilitate
connections to fluid flow passageways through which the rate of
fluid flow is to be measured;
said second rotor being positioned by a rotor spacer a short distance
downstream from said first rotor and adjacent said pickoff coil;
said first and second rotors having oppositely canted vanes which
cause said first and second rotors to rotate in opposite directions
when a fluid entering said inlet port passes through said first
and second rotors and exits said outlet port;
said second rotor having said vanes that are made from a magnetic
whereby a fluid flowing through said first and second rotors causes
said first and second rotors to turn at velocities proportional
to the rate of fluid flow through said flow meter, said vanes of
said second rotor passing through the magnetic field of said pickoff
coil causing pulses to be superimposed upon said carrier frequency
of said a-c signal of said pickoff coil, the repetition rate of
said pulses being proportional to the flow rate of said fluid flowing
through said flow meter and said repetition rate being convertible
to rate of flow values by an external flow rate computer;
said first rotor serving to precondition and alter the flow pattern
at the entrance of said second rotor in such a way as to extend
the effective metering range to lower flow rates and providing improved
accuracy and linearity at such lower flow rates of fluid flow.
2. The turbine type flow meter set forth in claim 1 in further
first and second transition deflectors;
first and second straighteners, and a rotor spacer;
said rotor spacer being mounted on said shaft between said first
and second rotors and defining the spacing between said first and
said first transition deflector being mounted immediately upstream
from said first rotor;
said second transition deflector being mounted immediately downstream
from said second rotor;
said first flow straightener being mounted immediately upstream
from said first transition deflector and;
said second flow straightener being mounted immediately downstream
from said second transition deflector;
whereby said first and second transition deflectors serve to reduce
fluid turbulence at the fluid entrance of said first rotor and at
the fluid exhaust of said second rotor; and
said first and second flow straighteners serve as means for mounting
said shaft of said flow meter in addition to straightening the flow
patterns at said inlet and outlet ports of said flow meter.
3. The turbine type flow meter set forth in claim 1 wherein:
said second rotor is designed to rotate at a somewhat higher velocity
than the rotational velocity of said first rotor, the difference
in said two rotational velocities being more noticeable at the lower
end of the metered range.
4. The turbine type flow meter set forth in claim 2 wherein:
said second rotor is designed to rotate at a somewhat higher velocity
than that of said first rotor.
BACKGROUND OF THE INVENTION
This invention relates to flow meters of the turbine variety wherein
a rotor is turned by the fluid being measured. The turbine rotor
turns at a velocity proportional to the rate of flow. The vanes
of the rotor passing through the magnetic field of a pickoff coil
generate a pulsating signal in the pickoff coil at a frequency that
is proportional to the flow rate.
DESCRIPTION OF THE PRIOR ART
Prior art turbine type flow meters typically comprise a single
rotor with its pickoff coil together with various means for the
preconditioning of the flow pattern ahead of the turbine. While
such prior art turbine type flow meters are superior to most other
types of flow meters, they still leave considerable room for improved
performance in terms of accuracy, linearity, minimization of initial
calibration requirements, and especially in terms of measurement
SUMMARY OF THE INVENTION
This invention relates to turbine type flow meters incorporating
means ahead of the main turbine rotor for optimally shaping and
directing the flow pattern as the fluid enters the main rotor.
It is, therefore, one object of the present invention to provide
a turbine type flow meter that provides improved accuracy relative
to prior art turbine type flow meters.
Another object of this invention is to provide a turbine type flow
meter that exhibits improved accuracy over a wider range of fluid
flow rates without resort to excessively high revolutions per minute
at the maximum rate of flow, such excessively high revolutions per
minute being undesirable as they adversely affect bearing life of
the turbine flow meter.
A still further object of this invention is to provide a turbine
type flow meter that provides improved linearity over the total
A still further object of this invention is to provide such an
improved turbine type flow meter in a form that eliminates the need
for initial calibrations involving the tweaking or filing of rotor
blades, bending of straightener vanes, etc. to obtain wide range
A still further object of this invention is to achieve such improved
performance through the incorporation of an auxiliary, oppositely
turning rotor ahead of or upstream from the main rotor, the auxiliary
rotor serving as the primary means for appropriately directing the
flow pattern of the fluid as it enters the main rotor.
Further objects and advantages of the invention will become apparent
as the following description proceeds and the features of novelty
which characterize his invention will be pointed out with particularity
in the claims annexed to and forming a part of this specification.
BRIEF DESCRIPTION OF THE DRAWING
The present invention may be more readily described with reference
to the accompanying drawing in which:
FIG. 1 is a simplified side view of the improved flow meter of
the invention with the housing cut away to reveal details of the
FIG. 2 is a cross-sectional view of the flow meter taken along
line 2--2 of FIG. 1 showing the configuration of a flow straightener
incorporated in the flow meter of FIG. 1;
FIG. 3 is a perspective view of a transition deflector incorporated
in the flow meter of FIG. 1;
FIG. 4A is an end view of the main rotor incorporated in the flow
meter of FIG. 1;
FIG. 4B is a side view of the main rotor incorporated in the flow
meter of FIG. 1;
FIG. 5 illustrates the effect of the auxiliary rotor upon the flow
pattern of the fluid as it enters the main rotor; and
FIG. 6 shows the magnetic field of the pickoff coil as it links
a passing vane of the main rotor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to the drawings by characters of reference,
FIGS. 1-4 disclose the improved flow meter 10 of the invention,
the flow meter 10 comprising a generally cylindrical housing 11
a shaft 12 an upstream flow straightener 13 a downstream flow
straightener 14 an upstream transition deflector 15 a downstream
transition deflector 16 a main rotor 17 an auxiliary rotor 18
rotor bearings 19 and 21 bearing spacers 22 and 23 a rotor spacer
24 a pickoff coil 25 standard retainer 26 and lock nut 27.
Housing 11 has a cylindrical longitudinal opening, the central
part of which provides clearance for the free rotation of rotors
17 and 18. The inside diameter of this central part is somewhat
smaller than the overall outside dimensions of the flow straighteners
13 and 14. At both ends, the inside diameter of the housing is somewhat
greater than in the central part and just great enough to receive
the flow straighteners 13 and 14 in a snug fit. At the junctions
of the smaller diameter of the central part with the larger diameter
of the end sections retaining shoulders 28 are formed. The length
of the central part is just great enough to receive the two rotors
17 and 18 the rotor spacer 24 and the two transition deflectors
15 and 16; the enlarged outer sections are long enough to receive
the flow straighteners 13 and 14.
Shaft 12 has the form of a bolt threaded at the end to mate with
matching threads in the central opening 29 of flow straightener
14. The diameter of shaft 12 is just small enough to receive the
central circular openings of flow straightener 13 transition deflectors
15 and 16 rotor spacer 24 and the bearings 19 and 21 of rotors
17 and 18. The inlet and outlet ends of the housing are adapted
for connection to the fluid lines.
In the assembly of the flow meter 10 the flow straightener 13
transition deflector 15 rotor 18 with its bearing 21 and bearing
spacer 23 rotor spacer 24 rotor 17 with its bearing 19 and bearing
spacer 22 and transition deflector 16 are first slipped in place
over shaft 12 in the order just given. This subassembly is inserted
into the inlet side of the housing 11. Straightener 14 is then inserted
into the outlet opening of housing 11 and the threaded end of shaft
12 is turned into the threaded central opening of straightener 14.
As this threaded connection is tightened, the straighteners 13 and
14 are driven inwardly until their inboard outer diameters bear
against the shoulders 28. The positioning of the straighteners 13
and 14 upon shaft 12 against the shoulders 28 is further illustrated
by FIG. 2. The shaft 12 and the parts assembled thereon are now
centrally supported at both ends by straighteners 13 and 14.
As shown in FIG. 1 with the above assembled parts in place as
just described, the pickoff coil 25 is located directly above the
main rotor 17 with its axis directed downward so that the passing
vanes of the rotor 17 move through the magnetic field of coil 25
as the rotor 17 revolves. The coil 25 is held in this position by
its cylindrical retainer 26 which is threaded into an opening in
shell 11 and secured therein by lock nut 27. Transition deflector
15 as shown in FIGS. 1 and 3 has a cylindrical section 31 followed
by a conical section 32. This configuration tends to provide a smooth
transition between the deeper opening of straightener 13 and the
shallower opening of rotor 18 with the flow pattern 33 being driven
radially outward as shown in FIG. 3.
The rotor assembly 30 is more clearly shown in FIGS. 4A and 4B
where rotor 17 is shown to have canted vanes 34 evenly spaced about
its periphery. The rotor bearing 19 fits snugly over shaft 12 the
bearing spacer 22 fits securely over shaft 12 and between bearings
19 and rotor 17 fits securely over bearing 19. The rotational velocity
of the rotor at a given flow rate is dependent upon the number of
vanes, the dimensions of the vanes and the angle 35 at which the
vanes are mounted. The rotor is made of a magnetic material.
In the operation of the flow meter 10 fluid enters at the inlet
end of the meter from the upstream fluid lines as shown in FIG.
1 passing between the vanes 36 of straightener 13 which tend to
reduce any turbulence that may be present in the entering fluid.
As the fluid exits the straightener 13 it is deflected outwardly
by the conical section 32 of transition deflector 15. This reduces
turbulence that would otherwise be introduced by an abrupt change
in the fluid opening between deflector 15 and rotor 18.
As the fluid then passes through auxiliary rotor 18 rotor spacer
24 and main rotor 17 the flow pattern is conditioned in accordance
with the principles of the present invention as illustrated in FIG.
5. Ideally, fluid enters in a direction parallel with the axis of
the flow meter 10 as indicated in FIG. 5 by flow indicators 37.
The vanes 34 of rotors 17 and 18 are canted oppositely as shown
in FIG. 5. This causes the two rotors to be turned in opposite directions
by the passing fluid. Rotation directions for rotors 18 and 17 are
indicated, respectively, by rotation indicators 38 and 39. In the
process of driving auxiliary rotor 18 in the direction indicated
the flow pattern is converted into a swirling pattern as indicated
by flow indicators 41. It will be noted that the swirling pattern
shown by indicators 41 has rotational energy in a direction opposite
the rotational direction 38 of auxiliary rotor 18 and in the same
direction as the rotation of rotor 17. This added rotational energy
is absorbed by main rotor 17 and is manifested as increased rotational
velocity for rotor 17.
The benefit of this enhanced driving force and increased rotational
velocity for the main rotor 17 is felt most importantly at low fluid
flow rates where bearing friction and other inefficiencies most
seriously affect accuracy, linearity and rangeability. By virtue
of the improved performance achieved through this preconditioning
function of the auxiliary rotor the effective range of the flow
meter is extended to lower flow rates than have been achieved in
prior art flow meters.
In the design of the two rotors, 17 and 18 the main rotor 17 is
designed to rotate at a higher velocity than that of the auxiliary
rotor 18. This has been found desirable in terms of maximizing the
improvements claimed for the present invention. In a particular
implementation at relatively high flow rates, the velocity of the
main rotor was found to be roughly 12 percent higher than that of
the auxiliary rotor; at the low end of the range with quite a low
flow rate, the main rotor velocity was as much as 27 percent higher
than that of the auxiliary rotor. This increase in relative velocity
for the main rotor at low flow rates verifies and further explains
the improvement in accuracy and linearity obtained in the present
The spacing between the two rotors is also important. If the spacing
is too close the two rotors tend to interfere hydraulically with
each other. If they are too far apart, the flow pattern tends to
lose its angular approach. The spacing has been optimized experimentally
in existing designs of the flow meter.
When the foregoing design guidelines are observed, there is no
need for mechanical calibration of the manufactured product involving
the filing of rotor vanes or straightener vanes.
Referring again to FIG. 1 fluid flowing downstream from the main
rotor 17 passes over deflector 16 and through straightener 14 to
the flow meter outlet to the downstream piping. Deflector 16 again
provides a smooth transition between rotor 17 and straightener 14
thereby reducing turbulence that might otherwise be reflected upstream
with adverse effects on meter performance.
As in prior art turbine type flow meters, the rotational velocity
of the main rotor 17 is sensed by pickoff coil 25. The pickoff coil
25 is excited by an a-c signal or carrier, typically at a frequency
on the order of 60 kilohertz. This signal produces a magnetic field
42 as shown in FIG. 6. As the main rotor turns, its vanes 34 pass
through the field 42 each successive vane superimposing a pulse
upon the carrier waveform of the pickoff coil. The superimposed
pulses occur at a repetition rate (pulses per second) proportional
to rotor velocity and hence proportional to the measured rate of
fluid flow. An external flow rate computer makes the conversion
and registers the measured flow rate.
Variations and extensions of the present invention are contemplated
and are considered to fall within the scope of the invention.
While the present invention utilizes a single pickoff coil to sense
the rotation of the main rotor, a second pickoff coil can be added
to sense the rotation of the auxiliary rotor. With both signals
available, a failure or malfunction of either rotor would be evidenced
through a comparison of the two readings. This effective redundancy
provides improved reliability for critical applications. For such
applications, two prior art flow meters are typically connected
in series. The two-coil version of the present invention can thus
constitute a cost saving over the prior art.
The flow meter of the present invention has thus been shown to
provide improved range, accuracy, linearity and reliability over
prior art designs.