A flow meter for detecting and recording a plurality of data points
representative of the depth and velocity of liquid flow in an open
container. A weighted sensor has a dimpled surface to induce turbulence
at low velocities to assure a substantially linear velocity characteristic.
An electromagnetic velocity transducer and a single tube bubbler
are engaged to the sensor to provide data which is periodically
read into a cassette recorder. A microcomputer controls timing functions
with respect to the collection and recordation of data within the
What is claimed is:
1. A flow meter for gathering a plurality of discrete data points
characterizing the flow of liquid in an open channel comprising:
sensor means including separate transducer means for sensing the
depth and the velocity of flow of said liquid, said sensor means
having upper and lower spaced apart surfaces, said lower surface
defining a port therein, and said sensor means having sufficient
weight to be positioned with said lower surface at the bottom of
said channel and to remain substantially stationary therein without
restraint while said liquid flows thereover;
said depth sensing transducer means including means for providing
intermittent pulses of pressurized gas to said port; and
said velocity sensing transducer means including means for establishing
a magnetic field at said upper means for establishing a magnetic
field at said upper surface and measuring electrodes terminating
at said upper surface for generating electrical signals representative
of liquid flow velocity responsive to the flow of said liquid across
said upper surface.
2. A flow meter as defined in claim 1 wherein said upper surface
defines a plurality of irregularities therein.
3. The flow meter as defined in claim 2 wherein said irregularities
4. A flow meter as defined in claim 1 which further includes a
recess defined by said lower surface, said port terminating at said
5. A flow meter as defined in claim 4 wherein said means for providing
intermittent pulses includes a self-contained source of pressurized
gas, tube means interconnecting said gas source and said port valve
means disposed with said tube means for controlling the flow of
gas to said port in pulses, and means for periodically activating
said valve to supply periodic pulses of gas to said port.
6. A flow meter as defined in claim 5 wherein said tube means is
a single tube and which further includes means connected to said
tube means for measuring pressure to determine the depth of said
7. A flow meter as defined in claim 1 wherein said magnetic field
establishing means includes pole pieces terminating at said upper
surface and said measuring electrodes are disposed adjacent said
pole pieces at said upper surface.
8. A flow meter as defined in claim 7 which further includes a
generally E-shaped core of magnetic material with the base thereof
adjacent said lower surface and the tips of the legs thereof at
said upper surface.
9. A flow meter as defined in claim 8 which further includes a
pair of conductors of equal length connected between a common point
and each measuring electrode for eliminating current loops.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention pertains to fluid flow measurement. More
particularly, it pertains to apparatus and methods for gauging the
flow of liquid in an open channel.
2. Description of the Prior Art
The need for systems and methods to measure open channel liquid
flow has existed for a long time. The volumetric flows of aqueducts,
canals, and viaducts must be closely monitored. Pipelines transporting
sewage often are maintained in an open channel state, the amount
of effluent failing to fill the cross section of the sewage pipe.
The determination of a flow rate in an open channel requires knowledge
of both the velocity and depth of the flowing liquid. Mathematical
computations may then be performed upon the velocity and depth data
to drive the volumetric flow rate.
The acquisition of the necessary variables has produced a substantial
volume of technology. Liquid depth gauges of the air bubble type
are disclosed in U.S. Pat. No. 3638490 of Buettnes, U.S. Pat.
No. 3475959 of Glassey and U.S. Pat. No. 3587316 of Kapteyn.
Flow measuring devices using electromagnetic probes are disclosed
in U.S. Pat. Nos. 3885433 to Marsh, Darby No. 3898881 Sturgeon
U.S. Pat. No. 2949551 Rolf et al U.S. Pat. No. 3757576 and
Banks U.S. Pat. No. 3802262. U.S. Pat. No. 4083243 issued Apr.
11 1978 Lawrence B. Marsh discloses a system that includes means
for recording true volume flow without the necessity or empirical
The present invention provides a substantial advance in the flow
measurement art by providing an improved flow meter for gathering
a plurality of discrete data points characterizing the flow of liquid
in an open channel. The meter includes means for measuring the velocity
of the liquid and means for measuring its depth. A recorder is provided.
A microcomputer provides substantial control of the system. The
microcomputer directs the measured values of the velocity and the
depth of the liquid at predetermined times to the recorder to produce
a time record of the flow of liquid in the open channel.
These and other advantages and features of the present invention
will become apparent in conjunction with the following detailed
description wherein like numerals represent like parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 discloses, in schematic format, the overall system comprising
the flow meter and recorder;
FIG. 2 is a schematic view of the single hose depth detection apparatus
utilized in the flow meter;
FIG. 3 is a graph for use in illustrating the pulsed operation
of the single hose depth detection apparatus of FIG. 2;
FIGS. 4A and 4B are side and plan views, respectively, of the velocity
transducer of the flow meter system of FIG. 1;
FIGS. 5A and 5B present enlarged side and top views, respectively,
of the hydrodynamic sensor utilized in conjunction with the flow
meter and associated depth and velocity detection apparatus of the
Turning now to the drawings, FIG. 1 is a general schematic view
of the overall flow metering system of the invention. In the discussion
to follow, various features of the metering system will be discussed
in greater detail with particular emphasis upon subsystems and methods
which constitute additional inventions over the prior art. The metering
system disclosed in FIG. 1 produces a plurality of velocity and
depth data points indicative of the flow within an open channel
(that is, a pipe or other conduit whose cross section is not filled
by the flowing liquid.)
Once gathered, the data may be entered on a magnetic tape or the
like for future study and analysis. A microcomputer 10 provides
an essential element of the metering system. Although a number of
commercially available devices may be employed, a low power device
such as model 1802 by the Radio Corporation of America of Princeton,
N.J., if preferred. The microcomputer 10 controls the depth measurement
apparatus by controlling a solenoid valve 12. The solenoid valve
12 regulates the passage of pressurized gas from a source 14 into
tubing 16. As will be discussed to a greater extent with respect
to FIGS. 2 and 3 the signal from the microcomputer 10 is designed
to produce "pulses" of pressurized gas of very short duration.
Gas flowing through the tubing 16 exits a sensor 18 at an underside
port 20. The sensor 18 is placed at the bottom of the flow channel
during operation and will be discussed with particular detail in
regard to FIGS. 5A and 5B.
A conventional differential pressure transducer 22 having atmospheric
vent 24 is engaged to the tubing 16. Responsive to the pressure
within the tubing 16 the output of the transducer 22 a voltage
representative of the pressure above or below atmospheric pressure
within the tubing 16 is applied to an amplifier 26 the value of
which is calibrated to convert the pressure reading to an analog
voltage representative the depth of liquid.
The voltage output of the amplifier 26 is applied to one port of
a multiplexer 28. The other input to the multiplexer 28 comes from
a differential amplifier 30. This signal, an amplitude modulated
A.C. signal, is derived by the modulation of a sinusoid from a (magnetic
field-activating) oscillator 32 by the electric field induced in
a velocity transducer (not shown in FIG. 1) in response to flow
over the sensor 18. The operation of the transducer will be disclosed
further in the discussion accompanying FIGS. 4A and 4B. The method
of mounting its electrodes within the sensor 18 will become apparent
with respect to FIG. 5B.
The multiplexer 28 is controlled by the microcomputer 10 so that
a signal representative of one or the other of the monitored variables
may be selectively read into an analog-to-digital converter 34 in
accordance with the state of the signal applied at its selector
(A/B) port. The converter 34 receives a pair of "start conversion"
pulses at every data point. The microcomputer 10 is programmed to
change the state of the signal at the A/B port of the multiplexer
38 between the paired "start conversion" pulses so both
a velocity and a depth data point will be converted to digital form
for application to the microcomputer 10.
Upon entry of the digital data into the microcomputer 10 the data
is formatted for compatibility with a recorder 36. The recorder
36 may be any of a number of conventional devices including those
that produce a magnetic data record on a standard cassette or the
FIG. 2 illustrates the depth measurement mechanism in operation.
As mentioned above, the fact that the metering system is employed
for flow measurement in an open channel necessitates the measurement
of data points containing both depth and velocity information. It
is well known that the depth H of a liquid body is a linear function
of the pressure of the liquid at the bottom 38 of its container.
Hence, by measuring the pressure at the bottom of the sensor 18
one may obtain an indication of the depth of the channel.
It is well known in the art that, by bubbling a gas out a tube
submerged in a liquid, a pressure equilibrum may be established
so that the pressure of the liquid may be determined from gas pressure
within the tube. Devices known as "bubblers" have been
employed to take advantage of this principle. A representative example
of such a bubbler according to the prior art is disclosed in U.S.
Pat. No. 3587316 of Bastiaan Kapteyn issued June 28 1971 for
"Bubble Pipe Attachment."
The prior art has taught that the use of a single tube bubbler,
such as that of applicants herein, is fraught with difficulties
due to the substantial viscosity of the gas flow in the tube. As
a result, unless the diameter of the tube is made impracticably
large, it is well known that a pressure transducer will not measure
the pressure at the bottom of the single tube but rather the pressure
differential existing along its length. Thus inaccuracies and nonlinearities
were formerly believed to be inherent in a single tube system. To
overcome this difficulty, it has been a common practice in the art
to employ a second or static tube in communication with the transducer
and with the lower end of the tubing. As no pressure is applied
to the static tube, its pressure reflects the pressure at the lower
end of the other tube. Unfortunately, such a static tube is generally
inappropriate for a bacteria-ladden environment such as a sewer
containing substantial quantities of nutrients. Often the bacteria
enter the static tube, which is often near or below the surface
of the liquid. Once within the tube, they quickly multiply, blocking
the device and rendering it useless.
Applicants have overcome the aforesaid difficulty by utilizing
the microcomputer 10 as a controller in a new method for operating
a single tube bubbler. Utilizing the apparatus of FIG. 2 applicants
employ the microcomputer 10 to open the solenoid valve 12 at regular
intervals of short duration. In a preferred embodiment the microcomputer
10 was programmed to open the valve 12 every 5 minutes for about
52 milliseconds. In this manner, a pulse of gas was fed into the
tube 16 from a pressurized cannister (acting as the source 14) under
a pressure of 57 p.s.i. (It is to be noted that the pulsed system
of the invention, as opposed to conventional continuous bubbler
systems, requires no gas compressor-a bulky energy consumer). By
quickly turning off the flow, a static pressure equilibrium is established
throughout the length of the tube as soon as the escape of gas bubbles
ceases. Thus no gas flow occurs between the transducer 22 and the
end of the tube 16. Hence, the reading of the transducer 22 is unaffected
by any pressure head due to the viscosity of continuously flowing
FIG. 3 is a graph illustrating the detection of pressure at the
bottom 38 of a liquid-containing vessel according to the invention
of FIG. 2. Applicants have found that the method, featuring the
application of a pressure pulse from the gas source 14 followed
by a few seconds' settling time to allow the bubbling from the bottom
of the sensor 18 to cease, will result in accurate measurement of
the pressure, and hence the depth of the liquid.
In FIG. 3 the solid line represents the acutal pressure existing
at the bottom of the body of liquid while the dashed line represents
the pressure sensed by the transducer 22. One can see that, during
the initial 5 minute segment, the depth of the liquid has increased,
increasing the pressure at the bottom of the sensor 18. The transducer
22 is able to sense a portion of this increase as a quantity of
the liquid intrudes into the tube 16 compressing and increasing
the pressure of the gas remaining in the tube 16. At the end of
the 5 minute interval, a signal from the microcomputer 10 opens
the valve 12 causing pressurized gas to enter the tube 16. This
increases the tube pressure (detected by the transducer 22) to P1
somewhat greater than the actual pressure of the liquid. As a pressure
disequilibrum now exists at the bottom of the sensor 18 a portion
of the gas within the tube 16 will bubble out until such time as
the pressure equilibrum is reestablished. This occurs generally
after a few seconds. The microcomputer 10 is programmed to "wait"
an appropriate time interval (about 5 seconds) for the reestablishmentof
equilibrum before applying a "start conversion" signal
to the analog-to-digital converter 34. The pressure P2 indicates
the pressure data point (converted to a depth data point by an appropriate
scale factor designed into the amplifier 26) which will eventually
be applied to the recorder 36. Thus an accurate data sample is obtained
by the non-continuous pulsed method of operating a single tube bubbler.
The transducer 22 is able to track pressure accurately during periods
of declining liquid depth (and consequently decreasing pressure
as seen in FIG. 3) even without the aid of an equilibrium-restoring
pulse from the source 14. This is due to the fact that decreasing
liquid pressure allows the bubbling out of gas trapped in the tube
16 until an equilibrium pressure is re-established. Thus, in this
situation, the programmed pulse of gas (at P3 or P4), while not
harmful, adds nothing to the accurate measurement of pressure and
FIGS. 4A and 4B are side and plan views respectively of the electromagnetic
velocity transducer 40. The transducer is mounted in the sensor
18. It comprises a pair of U shaped cores 4244 of high magnetic
permeability. Alternatively, the core might be a single piece formed
into two U shapes having a common leg. The pole pieces of the cores
42 and 44 are closely spaced to minimize air gaps therebetween.
A coil 46 circles the inner legs of the core pieces 4244. Alternating
current in the coil 46 supplied by the osillator 32 produces magnetic
flux throughout the core pieces and in free space as indicated by
the field lines 48 and 50. The resultant magnetic field vector B
is indicated, pointing upwards from the middle of the transducer
40. (Of course, when the current in the coil 46 is reversed, all
magnetic field lines are reversed).
The coil 46 is wound upon plastic bobbin 52 insulating the wires
of the coil from the core pieces. Three electrodes 54 56 and 58
are secured on the top of the bobbin by means of expoxy glue or
the like. It will be seen that the electrodes extend through the
upper surface of sensor to provide an electrical circuit including
the flowing liquid as a conductor.
As one can see from FIG. 4B, the pole pieces 4244 are coplanar
and arranged transverse to the direction of flow, indicated by the
velocity vector V, when mounted within the polyurethane sensor 18.
The measuring electrodes 5458 lie at opposite ends of the electric
field lines which result from the interaction of the magnetic field
(generated by the electromagnetic comprising the U-shaped cores
4244 and coil 46) with the moving conductor (comprising the flow
of the liquid between the electrodes.) Stated in quasi-mathematical
terms, the electrodes 5458 are aligned in the direction of the
cross product of the velocity and the magnetic field. The third
electrode 56 supplies the common ground signal.
Since the electrodes 5458 lie at opposite ends of an electric
force field, a potential difference exists there across which provides
an indication of the velocity of the liquid. The voltage difference
across the electrodes is reversed each time the direction of the
B vector is reversed. Thus an A.C. signal modulated by a function
of velocity can be obtained by tapping the two measuring electrodes.
The conductors 6062 are soldered to the electrodes. A unique S-shaped
geometry is employed so that currents induced in the conductors
6062 as a result of the presence of the magnetic field of the transducer
40 cancel each other out. Without the unique arrangement of the
conductors 6062 employed in FIG. 4B, the conductivity of the liquid
would result in a current loop (through the water and the electrodes)
encircling the magnetic flux of transducer 40. The result of such
a loop would be to induce additive, spurious currents in the conductors
6062 regardless of liquid velocity. Thus it is seen that the velocity
transducer 40 achieves freedom from spurious low velocity signals,
is highly efficient (consuming little power due to its small air
gaps) and, as a result of its design which locates all pole pieces
near the overlying liquid to concentrate magnetic flux into the
liquid, it is unimpeded by the presence of conductors at its backside.
The last quality is of particular importance with respect to the
employment of the invention and sensor 18 within metallic sewer
FIGS. 5A and 5B are side and top views of the sensor 18. The sensor
is formed of molded polyurethane or like plastic. In addition a
weight is located within the sensor to assure that the device will
remain immobile and unaffected by the flow.
In operation, the sensor 18 is placed at the bottom of a sewer
line or the like. A vent 20 at its underside is provided for the
escape of the bubbles discussed with respect to the depth measuring
method. The tube 14 and an electrical cable containing information
from the velocity transducer 40 are contained within a flexible
cable 60 which connects the sensor 18 to associated support apparatus
The top view of FIG. 5B illustrates the electrodes 54 56 58 which
are mounted flush with the top of the sensor 18. As discussed above,
the measuring electrodes are mounted transverse to the flow of liquid
(indicated by V) for maximum transducer 40 sensitivity (the transducer
40 is located within the sensor 18 somewhat beneath the electrodes).
A plurality of dimples 62 is formed in the top surface of the sensor
18. The dimples serve to create a turbulent flow at low velocities.
By creating turbulent flow, the detection of velocity is somewhat
simplified as the apparatus of the invention may neglect the differing
flow coefficients associated with laminar flow and turbulent flow.
Thus a broader velocity range is obtained of linear flow characteristics.
Thus it is seen that there has been brought to the flow metering
art new and improved apparatus and methods.