Note: Descriptions are shown in the official language in which they were submitted.
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1
111ZPROVED METHOD AND APPARATUS FOR CALCULATING FLOW
RATES THROUGH A PUMPING STATION
This invention relates generally to a method and apparatus for determining a
reliable measurement of the flow of liquid through a system, for example a
sewage
system.
BACKGROUND OF THIS INVENTION
Among the prior patents, two may be singled out, these being U.S. patent No.
2,101,257, issued December 7, 1937 to M. Vogel-Jorgensen, for "Apparatus for
Measuring Liquid or Fluent Materials", and U.S. patent No. 2,392,951, issued
January 14, 1946 to R. G. Salisbury, and entitled "Flow Meter" . In the case
of both
of these patents, the concept is to provide a calibrated volume which may be
switched
into and out of the normal flow line for the liquid, allowing the flow rate to
be
monitored at timed intervals. A drawback of these prior art patents is that
the
calibrated volumes provide only an approximate idea of the total flow, and are
incapable of exact precision.
My own earlier U.S. patent No. 4,455,870, issued June 26, 1984 and entitled
"Method and Apparatus for Determining Liquid Flow Rates" attempts to solve the
problems inherent in the prior art mentioned above. My prior patent provides a
method for determining the total inflow of a liquid through a liquid-flow
system in
which the liquid enters a sump cavity and is pumped out of the sump cavity by
pump
means. A computer calculates an on-going total inflow volume for the liquid by
(1)
adding in the sump cavity volume between lower and upper limit levels each
time the
liquid surface rises to the upper limit level, and (2) determining the inflow
rate over
the last portion of the filling time just described and extrapolating this
inflow rate
over the time during which the pump means is operating, to yield an
incremental
quantity, such quantity being added into the ongoing total inflow volume.
The said earlier patent provided a satisfactory procedure for determining
total
inflow volume in a relatively reliable way, but in certain cases it was not as
accurate
as desired, especially when the inflow rate was changing more or less
dramatically
during the pumping cycle.
The latter problem was addressed by my U.S. patent 4,669,308, issued June
2, 1987, and entitled "Method and Apparatus for Determining Liquid Flow Rates"
.
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2
In this second patent, improved accuracy was obtained, but at the cost of
requiring
a significantly more complex apparatus. In brief, the solution offered by the
latter
patent was to calculate an inflow rate during a pumping phase by determining
the
inflow rate during two sequential intervals just prior to the pumping phase,
and over
two sequential intervals just after the pumping phase. For each pair of
intervals, the
flow rates were extrapolated either forward or backward (as the case may be)
for the
pumping phase in question, and the two extrapolated values were averaged
before
being multiplied by the duration of the pumping phase in order to arrive at a
total
volume entering during the pumping phase.
My further prior patent number 5,182,951, issued February 2, 1993, and
entitled "Method and Apparatus for Calculating Flow Rates Through a Pumping
Station" uses a different approach to calculating total flow volume. The
apparatus
includes at least one pump, and also includes, for each pump and for each
combination of pumps, an oscillator circuit of which the output frequency can
be
adjusted. The frequency of each such circuit is adjusted to represent the pump
rate
for the pump or combination of pumps to which that oscillator circuit
corresponds.
While operating the pumping station, a totalizer has fed to it the output
frequency of
that oscillator circuit which corresponds to the pump or combination of pumps
that
is operating in any given time, and the total in the totalizer is incremented
by a given
amount for each pulse encountered, thus continuously updating the totalizer.
My further U.S. patent No. 5,190,442, issued March 2, 1993, and entitled
"Electronic Pumpcontrol System", is an attempt to achieve greater
sophistication and
accuracy in a system incorporating a plurality of pumps which can be operated
individually or in various combinations. In view of the fact that most pumps
produce
a flow rate which varies depending upon backpressure, the inventive
combination set
forth in my latter patent senses backpressure and includes an addressable
memory for
storing pumping rate values vs. backpressure for each of the pumps. A
processor is
programmed such that, on high backpressure, the pump controller avoids pump
starts
that will not result in a net increase in the total pumping rate, whereas on a
decrease
in backpressure, the pump controller allows more pumps to start when called
for, and
allows for the starting of more pumps than the minimum necessary, in order to
decrease the duration of pumping. The pump controller avoids a pump start
under
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3
conditions which would result in the pump undergoing rapid on/off cycling, and
further the pump controller avoids starting and stopping the pumps on pressure
surges.
Summarizing the prior art, it can be said that total liquid flow determination
can be relatively accurately determined, but the accuracy comes at a
substantial cost
due to complexity. By contrast, the simpler arrangements generally fail to
provide
the kind of accuracy that is expected from a monitoring system of this kind.
GENERAL DESCRIPTION OF THIS INVENTION
In view of the drawbacks of the prior art, as set forth in the previous
section,
it is an object of one aspect of this invention to provide a method and
apparatus for
calculating flow rates through a pumping station which achieve very
respectable
accuracy at a relatively low cost.
More particularly, this invention provides a method for determining the total
flow of a liquid through a liquid-flow system in which the liquid enters a
container
and is pumped out of the container by pump means which includes at least two
pumps
that may operate independently or together, the volume pumping rate for at
least each
combination of pumps being known and stored in an addressable memory, the
method
comprising the steps:
(a) allowing the liquid surface in the container to rise between a
predetermined
lower limit level and a predetermined upper limit level while the pump means
is shut
off,
(b) detecting the arrival of the liquid surface at a predetermined
intermediate
level as it rises between the lower limit level and the upper limit level, the
liquid
volume between the lower and the intermediate levels being substantially the
same as
the liquid volume between the intermediate and the upper levels,
(c) detecting the arrival of the liquid surface at the upper limit level, and
upon
such arrival, signalling the pump means to begin the pumping phase utilizing
at least
one pump selected by the pump controller, sufficient to remove liquid from the
container faster than the inflow rate.
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(d) detecting the arrival of the liquid surface at the lower limit level, and
upon
such arrival, signalling the pump means to stop the pumping phase,
(e) again allowing the liquid surface to rise as in step (a) and repeating
steps
(b), (c) and (d) in sequence, and
(f) calculating an on-going total inflow volume for the liquid by:
(1) if only one pump is required under (c), calculating the inflow rate during
the pumping phase by averaging the inflow rate between the intermediate and
upper levels just prior to the pumping phase and the inflow rate between the
lower and intermediate levels just after the pumping phase, multiplying such
calculated inflow rate by the duration of the pumping phase to arrive at a
volume of liquid entering during the pumping phase, and adding in said
volume; then adding in the container volume; then calculating the outflow rate
(pump rate) by using the previously established average inflow rate (total
volume divided by pumptime plus the average inflow rate), then storing this
value in the addressable memory.
(2) or, if a plurality of pumps is required under (c), calculating the liquid
volume pumped during the pumping phase by consulting said addressable
memory to determine the stored volume pumping rate for the particular
plurality of pumps that is operating, multiplying such stored volume pumping
rate by the duration of the pumping phase to arrive at a composite volume of
liquid equalling the sum of the container volume and the liquid entering
during
the pumping phase, and adding in said composite volume.
Further, this invention provides an apparatus for determining the total flow
of
a liquid through a liquid-flow system which includes a container for receiving
the
liquid and pumping means by which the liquid is pumped out of the container
during
a pumping phase, the pumping means including at least two pumps and a control
means adapted to operate the pumps independently or together, and an
addressable
memory in which the volume pumping rate for at least each combination of pumps
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is stored, the apparatus comprising:
(a) first means for detecting the arrival of the liquid surface at a
predetermined
lower limit level as it drops during a pumping phase, and for generating a
signal
5 which turns off said pumping means,
(b) second means for detecting the arrival of the liquid surface at a
predetermined intermediate level as it rises from the lower limit level, while
the
pumping means is off,
(c) third means for detecting the arrival of the liquid surface at an upper
limit
level and for generating a signal which turns on said pumping means utilizing
at least
one pump sufficient to remove liquid from the container faster than the inflow
rate,
the liquid volume between the lower and the intermediate levels being
substantially
the same as the liquid volume between the intermediate and the upper levels,
whereby
the liquid surface continuously rises and falls between said upper and lower
limit
levels, and
(d) computing means for calculating an on-going total inflow volume for the
liquid by:
( 1 ) if only one pump is required under (c), calculating the inflow rate
during
the pumping phase by averaging the inflow rate between the intermediate and
upper levels just prior to the pumping phase and the inflow rate between the
lower and intermediate levels just after the pumping phase, multiplying such
calculated inflow rate by the duration of the pumping phase to arrive at a
further volume of liquid entering during the pumping phase, and adding in
said further volume; then adding in the container volume; then calculating the
outflow rate (pump rate) by using the previously established average inflow
rate (total volume divided by pumptime plus the average inflow rate), then
storing this value in the addressable memory.
(2) or, if a plurality of pumps is required under (c), calculating the liquid
volume pumped during the pumping phase by consulting said addressable
6
memory to determine the stored volume pumping rate for the particular
plurality of pumps that is operating, multiplying such stored volume pumping
rate by the duration of the pumping phase to arrive at a composite volume of
liquid equalling the sum of the container volume and the liquid entering
during
the pumping phase, and adding in said composite volume.
GENERAL DESCRIPTION OF THE DRAWINGS
One embodiment of this invention is illustrated in the accompanying drawings,
in which like numerals denote like parts throughout the several views, and in
which:
Figure 1 is a somewhat schematic, vertical sectional view through a sewage
pumping station incorporating the present invention; and
Figure 2 is a graphical illustration for the purpose of explaining the
calculation
steps involved in a portion of the method of this invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Attention is first directed to Figure 1, which shows a container 10 for liquid
(for example, a wetwell in a sewage system), and an inlet pipe 12 for the
inflow of
liquid entering the container 10. Means are provided for ascertaining the
liquid level
in the container 10 and for generating various signals as determined by the
liquid
level. The means for ascertaining the liquid level is represented in Figure 1
by the
vertically downward arrow 14 and various horizontal lines within the container
10,
later to be described.
Also provided in Figure 1 is a plurality of pumps 18, each having an inlet 20
communicating with the interior of the container 10, and each having an outlet
22
communicating with a common conduit 24 for liquid being pump out of the
container
10.
Figure 1 further shows a pump controller 26 for receiving signals along the
sensor line 14, and for starting and stopping the pumps 18. The pump
controller 26
may include a manual override control (not illustrated), and receives electric
power
along line 28.
Looking at the left in Figure 1, it will be seen that, within container 10,
there
are defined an upper limit level 30, a lower limit level 31, and an
intermediate level
32 which is located such that the liquid volume between levels 31 and 32 is
substantially the same as the liquid volume between the levels 32 and 30.
7
These lines are also represented in Figure 2, which is a graphical
representation with height along the vertical and time along the horizontal.
Also
shown in Figure 2, in a schematic way, are sensors 30a, 31a and 32a, which may
be
float switches or other equivalent devices.
Ultrasonic measuring means, represented in Figure 1 at the numeral 37, may
be utilized in place of the sensors 30a, 31a and 32a, or together with the
sensors.
A flowmeter 29 receives information along the line 29a from the pump
controller 26, and performs the necessary computations.
To the right in Figure 1 is shown a digital reporting facility 34 operated by
the flowmeter 29 along the line 36, and an analog recording modality 38
controlled
by the flowmeter 29 along the line 40. Remote computer 42 interacts with the
flowmeter 29 along the line 44, and is adapted to provide commands to and
obtain
information from the flowmeter 29. Box 43 represents an optional flow-
proportional
feed-pump for delivering an additive such as alum (causes clumping) to the
container
10.
The flowmeter 29 operates on a program which includes a "totalizer" function,
so that, at any given time, a total cumulative flow, as from a given point in
time, can
be displayed. The flowmeter 29 also includes an addressable memory in which
the
volume pumping rate for all possible combinations of two or more pumps 18 can
be
stored.
Figure 1 also illustrates a two-way communication, represented at 46.
An optional external totalizer display, operated by the flowmeter 29, is shown
at 48.
In accordance with the method of this invention, it is first assumed that the
liquid volume between levels 31 and 32 is known and is stored in the flowmeter
29,
along with the volume pumping rate for each combination of two or more pumps.
The method includes firstly allowing the liquid surface in the container 10
(for
example, a wetwell) to rise between the lower limit 31 and the upper limit 30,
while
the pumps 18 are shut off.
The arrival of the liquid surface at the intermediate level 32 is detected and
the flowmeter 29 records the time taken to rise between levels 31 and 32.
The time of arrival of the liquid surface at the upper limit level 30 is also
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recorded by the flowmeter 29. Upon such arrival at the upper limit level 30,
the
pump controller 26 selects and starts one or more pumps, including the lead
pump.
The pump or pumps 18 then remain on until the liquid level falls to the lower
limit level 31, whereupon the pump means is signalled to stop. The previous
steps
are then repeated in sequence, and the result is that the liquid level
continuously
moves up and down between the upper and lower limit levels.
The flowmeter 29 is adapted to calculate the on-going total inflow volume for
the liquid by:
(1) if only one pump is required, calculating the inflow rate during the
pumping phase by averaging the inflow rate between the intermediate
and upper levels just prior to the pumping phase and the inflow rate
between the lower and intermediate levels just after the pumping
phase, multiplying such calculated averaged inflow rate by the duration
of the pumping phase to arrive at a volume of liquid entering during
the pumping phase, and adding in said volume to the totalizer; then
adding in the container volume; then calculating the outflow rate
(pump rate) by using the previously established average inflow rate
(total volume divided by pumptime plus the average inflow rate), then
storing this value in the addressable memory.
(2) or, if a plurality of pumps is required, calculating the liquid volume
pumped during the pumping phase by consulting the addressable
memory to determine the stored volume pumping rate for the particular
plurality of pumps that is operating, multiplying such stored volume
pumping rate by the duration of the pumping phase to arrive at a
composite volume of liquid equalling the sum of the container volume
and the liquid entering during the pumping phase, and adding in said
composite volume to the totalizer.
The diagram of Figure 2 covers approximately two complete cycles of the kind
just described. Note that the container volume is added under (1) only if a
single
pump is required. The container volume does not need to be added under (2),
because the method of calculation includes the container volume, due to the
fact that
the pumps not only discharge the liquid entering during the pumping phase, but
also
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the "container volume" of liquid already in the container when the pumps are
started.
In the first fill phase, the liquid level rises from level 31 to level 32 and
the
time lapse between the corresponding points 50 and 52 is noted. Likewise, the
time
lapse between points 52 and 54 is also noted, the latter representing arrival
of the
liquid level at the upper limit level 30. At the point 54, the pumping phase
is
initiated. During the pump phase, the liquid level falls from point 54 through
point
56 (representing the intermediate level 32), finally arriving at point 58,
representing
the lower limit level. Upon arrival at the lower limit level, the pump or
pumps are
shut off, and the liquid is allowed to accumulate in the container 10, with
the level
arriving at the intermediate location represented by point 60, and
subsequently
arriving at the point 62, whereupon the pumping phase is again initiated.
It will be noted in Figure 2 that the line representing the liquid level as it
rises
and falls has a steeper slope between the levels 32 and 30 than it has between
the
levels 31 and 32 (points 50, 52 and 54). This means that the inflow rate of
liquid at
the inlet 12 is increasing in the first fill phase represented in Figure 2.
After the
ensuing pump phase is completed (points 54 to 58), the slope of the line is
again
slightly increased between the points 58 and 60, but then markedly decreased
between
60 and 62.
In the example shown in Figure 2, assuming only one pump is operating
during the pump phase, the flowmeter 29 would average the calculated inflow
rate
between points 52 and 54 on the one hand, and the calculated inflow rate
between
points 58 and 60 on the other hand, and use the average of these two rates,
along
with the time during which the pump phase is "on", to calculate the total
inflow
during the pump phase.
It will thus be appreciated that, with a relatively simple apparatus, a
considerable degree of accuracy is attained in the calculation of total
accumulated
flow through the container 10.
While one embodiment of this invention has been illustrated in the
accompanying drawings and described hereinabove, it will be evident to those
skilled
in the art that changes and modifications may be made therein without
departing from
the present invention, as set forth in the appended claims.
