Abstrict A fluid flow meter with two independantly counter rotating turbine
impellers is disclosed in which fluid characteristics and/or upstream
flow disturbances cause minimal variations in volume flow rate measurements
by the meter as a result of fluidynamic interaction between the
impellers. The angular velocities of each of the impellers are sensed
in a conventional manner after which the velocity signals are added
to indicate a total volume thruput, and/or rate of flow, and optionally
compared to indicate an occurance of mechanical or electronic degradation.
Claims What is claimed is:
1. A meter for measuring fluid flow comprising:
a. A fluid conduit;
b. shaft support means mounted within said conduit;
c. a shaft axially mounted on said shaft support means;
d. a first turbine impeller having a plurality of blades rotatably
mounted in said conduit on said shaft;
e. a second turbine impeller having a plurality of blades rotatably
mounted in said conduit on said shaft, said second turbine impeller
mounted proximate and downstream from said first turbine impeller,
said second turbine impeller free to respond to any fluidynamic
aberration developed from said first turbine impeller, said second
turbine impeller arranged to rotate in a direction opposite that
of said first turbine impeller;
f. first sensing means for sensing the angular velocity of said
first turbine impeller; and
g. second sensing means for sensing the angular velocity of said
second turbine impeller.
2. The apparatus of claim 1 wherein said first turbine impeller
is integral with said shaft, said shaft rotates on said support
means, and said second turbine impeller rotates on said shaft.
3. The apparatus of claim 1 wherein said second turbine impeller
is integral with said shaft, said shaft rotates on said support
means, and said first turbine impeller rotates on said shaft.
4. The apparatus of claim 1 wherein said first and second sensing
means produce electrical signals and wherein said apparatus further
includes means to add said signals to produce an indication of the
fluid flow range through said meter.
5. The apparatus of claim 1 wherein said first and second sensing
means produce electrical signals and wherein said apparatus further
includes means to compare said signals to produce an indication
of malfunction.
6. The apparatus of claim 4 further including means to compare
said signals to produce an indication of malfunction.
7. The apparatus of claim 5 further including alarm means coupled
with said means to compare said signals to produce a warning of
said malfunction.
8. The apparatus of claim 6 further including alarm means coupled
with said means to compare said signals to produce a warning of
said malfunction.
9. A meter for measuring fluid flow comprising:
a. a fluid conduit;
b. a first shaft support means mounted within said conduit;
c. a second shaft support means mounted within said conduit;
d. a first shaft axially mounted on said first shaft support means;
e. a second shaft axially mounted on said second shaft support
means;
f. a first turbine impeller having a plurality of blades rotatably
mounted in said conduit on said first shaft;
g. a second turbine impeller having a plurality of blades rotatably
mounted in said conduit on said second shaft, said second turbine
impeller mounted proximate and downstream from said first turbine
impeller, said second impeller free to respond to any fluidynamic
aberration developed from first turbine impeller, said second turbine
impeller arranged to rotate in a direction opposite that of said
first turbine impeller;
h. first sensing means for sensing the angular velocity of said
first turbine impeller; and
i. second sensing means for sensing the angular velocity of said
second turbine impeller.
10. The apparatus of claim 9 wherein said first turbine impeller
is integral with said first shaft, said first shaft rotates on said
first support means, and said second turbine impeller rotates on
said second shaft.
11. The apparatus of claim 9 wherein said second turbine impeller
is integral with said second shaft, said second shaft rotates on
said first shaft.
12. The apparatus of claim 9 wherein said first and second sensing
means produce electrical signals and wherein said apparatus further
includes means to add said signals to produce an indication of the
fluid flow rate through said meter.
13. The apparatus of claim 9 wherein said first and second sensing
means produce electrical signals and wherein said apparatus further
includes means to compare said signals to produce an indication
of malfunction.
14. The apparatus of claim 9 further including means to compare
said signals to produce an indication of malfunction.
15. The apparatus of claim 13 further including alarm means coupled
with said means to compare said signals to produce a warning of
said malfunction.
16. The apparatus of claim 14 further including alarm means coupled
with said means to compare said signals to produce a warning of
said malfunction.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to fluid flow meters and more particularly
to flow meters which incorporate independently counter rotating
turbine impellers in the sensing mechanism.
2. Description of the Prior Art
A number of fluid flow meters utilizing rotating turbine impellers
are known in the prior art. In these devices, the meter is placed
in the line through which the flow is to be measured and the angular
velocity of the turbine, driven by the fluid flow, is measured and
correlated to the flow rate.
In prior art meters of this type, upstream disturbances in the
flow pattern produced a non-linear rotational velocity as related
to actual flow rate. This non-linearity reduced the reliability
and usefulness of these meters or required additional electronic
compensation to achieve an acceptable level of accuracy and range.
Also disclosed in the prior art are several designs in which an
additional turbine impeller or turbine shaped stator is interposed
in the flow path within the meter. One such prior art device, disclosed
in U.S. Pat. No. 3241366 adds a counter rotating impeller or
rotor upstream from the measuring rotor. This upstream rotor functions
only to direct the fluid flow on the blades of the principal or
measuring rotor. This upstream rotor termed a "compensating
rotor," requires a magnet and pins to effect a magnetic drag
on the compensating rotor which can be adjusted to extend the accuracy
of registration of the measuring rotor over an extended range of
flow rates.
In this disclosure, only the downstream rotor is a measuring rotor
and its performance curves will be substantially similar to those
disclosed and illustrated hereinafter for a downstream rotor or
impeller. The compensating rotor simply extends the measuring range
for conditions of low flow. The disclosure of the present invention
in which both impellers are measuring impellers, provides a simpler
construction which will achieve measurements at least equally reliable
and further includes self diagnostic means for early detection of
a malfunction.
Also, U.S. Pat. No. 3135116 reveals a dual turbine design in
which both rotors rotate in the same direction, one mounted piggyback
fashion on the rotating shaft of the other. A flow straightener
is interposed between the two turbines which acts, in contrast to
the present device, to fluid dynamically decouple the rotors.
U.S. Pat. No. 138657 discloses a meter having a dual augershaped
screw arrangement in which the upstream screw is stationary and
the forward or downstream screw revolves in response to flow through
the meter.
U.S. Pat. No. 470814 shows a similar arrangement including one
fixed and one rotating turbine - shaped deviced in which the blades
of each are angularly opposed to one another.
U.S. Pat. No. 3710622 discloses a dual rotor meter in which the
rotors have different parameters, rotate in the same direction and
are not fluid dynamically coupled.
The device described herein will be seen to be different in concept
and operation from the above or any other presently known to the
inventor.
SUMMARY OF THE INVENTION
The invention may be summarized as a fluid flow rate meter utilizing
two independantly counter rotating turbine impellers each of which
is a measuring impeller to overcome the nonlinearity of the single
impeller types resulting from upstream disturbances in the fluid
flow. Such disturbances are described or classed variously as turbulent
flow, viscous flow, velocity profile distortion, positive or negative
upstream swirl, and fluid viscosity.
Velocity profile distortion affects the operation of turbine meters,
and can speed up or slow down the angular velocity of impellers
as related to the average linear velocity of the fluid. Thus it
affects the calibration of the meter and can result in inaccurate
meter readings. In the design of the present invention, any changes
in angular velocity of the first impeller will result in an opposite
and equal change in the angular velocity of the second impeller.
Thus, averaging the angular velocity of both impellers will eliminate
inaccuracies caused by distortion in velocity profile and yield
a reasonably accurate reading within predetermined variances. Likewise,
increases in viscosity impose contrasting forces on impellers, one
of increasing the angular velocity as mentioned earlier, and the
other of decreasing the angular velocity due to the viscous drag
on the impeller blades. Viscous drag will slow each impeller, no
matter which direction it is rotating. However, in the present invention,
as the first impeller is being slowed by drag, the fluid will leave
the impeller blades with an angular velocity component which will
increase the speed of the second impeller. Thus, the averaging of
the angular velocities of both impellers will affect most of the
effect of increases in viscosity and minimize the calibration errors
resulting therefrom.
The impellers are preferably of equal size but oppositely canted,
the blades of one are arranged to produce a clockwise rotation,
while the blades of the other produce a counterclockwise rotation.
The impellers are mounted in proximity within a conduit such that
a change in angular velocity in the first due to upstream disturbance
produces an opposite change in the other. Adding the absolute value
of the two angular velocities and scaling the sum produces a highly
reliable flow rate measurement independant of any upstream disturbance.
The angular velocity signals may also be compared to indicate a
failure of one impeller or the other due to bearing friction, clogging
or other interference and the electronic signal detection - transmission
system. If one signal output exceeds another by a predetermined
amount during continuous comparison, a malfunction is indicated.
Alarm or warning systems may be incorporated into the comparison
circuitry to alert those monitoring the meter to the likelihood
of impending inaccurate readings based on turbine mechanical degeneration,
or electronic malfunction.
To explain the functioning of the meter of the present invention,
for example, where W.sub.1 and W.sub.2 represent the angular velocity
of each turbine impeller, W.sub. = W.sub.1 + W.sub.2 and, where
K is the sensing element constant, V is the flow rate, the addition
of W.sub.1 and W.sub.2 and relating the total to a volume rate:
##EQU1## the result will have extreme reliability, in that loss
of calibration can be easily detected and a fail safe circuit can
easily be provided. Furthermore, it will be relatively insensitive
to changes in viscosity, fluid swirl, and velocity profile.
Additionally, meter performance is critically related to various
factors such as bearing drag, blade angle and internal continuity.
A meter is calibrated before installation to determine the sensing
element constant, K. For the meter to be useful in service, the
meter must perform within certain predetermined limits. The utilization
of dual independant counter rotating turbine impellers, each of
which is a measuring impeller, in proximity to allow fluidynamic
interaction overcomes these problems. Any slowing of the first impeller
due to drag or bending of the impeller blades will have the effect
of increasing the angular velocity on the second impeller. A slowing
of the second impeller for the same reasons would minimize errors
since only one half of the deviation would be seen in the calibrated
resulting flow.
Also, the problem of malfunction is more readily determined in
the meter of the present invention. A divergence between W.sub.1
and W.sub.2 is determined during calibration. Any further significant
divergence can be discovered by monitoring the sensors, and if necessary,
the determination of a divergence beyond a preset limit could be
electronically connected to an alarm and/or control system.
The inherent features of the invention contribute substantially
to the reliability of in-line meters while reducing the complexity
of compensating necessary in prior art meters, thus yielding a more
satisfactory device at lower cost. These and other features of the
invention will become more apparent from the following description
of the preferred embodiment and the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical section A--A of a flow meter incorporating
the present invention;
FIG. 2 is an end view of the meter of FIG. 1;
FIG. 3 is a schematic diagram of electrical circuitry used in conjunction
with the meter;
FIG. 4 is a graphic representation of the flow rate of the meter
subjected to turbulent flow;
FIG. 5 is a graphic representation of the flow rate of the meter
subjected to viscous flow; and
FIG. 6 is a graphic representation of the flow rate of the meter
subjected to a positive upstream swirl.
FIG. 7 is a graphic representation of the flow rate of a composite
average of measured flow on two independent counter rotating turbine
impellers as disclosed in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1 there is shown a vertical section of
a flow meter utilizing the concept of the invention. A conduit is
formed of annular shaft supports 12 and 14 having support veins
16 and 18 respectively and turbine chamber ring 20 sealed to the
shaft supports by O-rings 22 and 24. The shaft supports and turbine
chamber ring are held in firm relationship by outer ring 26 and
flanges 28 and 30 joined to supports 12 and 14 by machine screws
32 and 34. Flanges 28 and 30 are further used to join the meter
to upstream and downstream portions of the flow line, not illustrated,
in a conventional manner. For that purpose, grooves 36 and 38 are
formed in shaft supports 12 and 14 to receive O-rings for sealing
against faces of flanged upstream and downstream flow lines.
Veins 16 and 18 of the shaft support bearings 40 and 42 which
veins and supports are tapered to prevent fluid turbulence within
the conduit. Shaft 44 may be left free to rotate on the bearings
or alternatively may be locked firmly in the bearing bodies, or
may be two separate shafts, one per impeller. If one shaft is used
it may be of the straddle type or cantilever type and if of the
cantilever type it may have either upstream support or downstream
support. If two shafts are used, each may be of the straddle type
or of the cantilever type and, if of the cantilever type, each may
have either upstream support or downstream support. A first turbine
impeller 46 having blades 48 is mounted on the shaft 44 and is arranged
to rotate in response to fluid flow through the meter. A second
turbine impeller 50 having blades 52 oppositely canted to blades
48 is mounted on shaft 44 and arranged to rotate oppositely from
impeller 46.
One or the other impeller may be fixed to the shaft if the shaft
is free to rotate within bearings 40 and 42 and the other impeller
allowed to rotate on the shaft. Optionally both impellers may be
left free to rotate on the shaft on bearings 54 and 56 as shown
in the drawing.
There can be fluidynamic interaction between the impellers by their
proximity in the conduit. By arranging them in this manner, it has
been found that they react to upstream disturbances oppositely,
that is, as one impeller falls below the velocity indicative of
the true fluid flow, the other rises above the velocity in reaction.
Sensors 58 and 60 magnetic sensors for example, function to count
the number of blades passing the sensor position as the impellers
rotate by emitting pulsed signals. The signals f1 and f2 are transmitted
along lines 62 and 64 to electronic circuitry for analysis as shown
in FIG. 3.
FIG. 2 illustrates the upstream end view of the meter incorporating
reference numerals and components as described above.
FIG. 3 shows this exemplary electronic circuitry in block diagram
format which may be used to determine total flow thruput, flow rate,
and failure occurrence in the meter. Upstream line 66 leads into
meter 10 and downstream line 68 out of meter 10. Sensors 58 and
60 produce pulse signals f1 and f2 indicative of the angular velocities
of the impellers. The pulses are added by anti-coincidence circuitry
70 and scaled by scaler 72.
The output of scaler 72 is fed to both totalizator indicator 82
and to rate of flow indicator 86 through the pulse/D.C. circuit
84. The totalizing indicator 82 and the rate of flow indicator 86
should give an accurate reading of the actual flow of fluids through
meter 10 as shown in FIG. 7.
Alternatively signals f1 and f2 may be fed to pulse/D.C. circuits
74 76 where the pulses from each sensor 58 60 are converted to
analog representations. Said representations are fed to alarm comparator
78. The comparator 78 may be set to activate a malfunction enunciator
80 when either signal deviates substantially from the other. As
described above, the angular velocities of the impellers 46 50
vary from each other in a plus - minus fashion to compensate for
flow stream disturbance, but neither should vary beyond a predetermined
amount which is sensed by the alarm comparator 78. When such a variation
beyond the set limits is encountered, it is indicative that one
of the turbines or electronic transmission circuits is reacting
improperly to the flow through clogging, bearing friction or other
irregularity, and that the likelihood of impending inaccurate readings
is at hand.
Also indicated on FIG. 1 are two velocity profile lines, one for
viscous fluid flow 90 and one for turbulent fluid flow 92.
Referring next to the graphs of FIGS. 4 5 6 and 7 the response
of the impellers and the meter to various upstream disturbances
is illustrated.
In each graph, it is evident that the independant and oppositely
rotating impellers act to mutually compensate each other when subjected
to upstream disturbance. As one speeds up, the other slows down
to produce the average flow indication depicted in the graphs.
Modifications of the above described device will be apparant to
those skilled in the art. Accordingly, the scope of the present
invention is defined by the following claims. |