Abstrict A flow meter for use with a fluid source includes a chamber of
known volume, and level sensors for detecting fluid boundaries at
either end of the known volume. A valve between the fluid source
and chamber is opened at a defined time until fluid level within
the chamber rises above the upper sensor, whereupon the valve is
closed. As the fluid level falls past the upper sensor a second
time level is measured, with both time intervals being terminated
as the level falls to the lower level sensor. The average flow rate
as the fluid falls between the two sensors is calculated by a computer,
and the total volume is then calculated using the longer measured
time interval. Flow rates over long time periods can be accurately
measured.
Claims What is claimed is:
1. Apparatus for injecting relatively small metered quantities
of fluid over relatively long periods of time, comprising:
a fluid source;
a chamber defining a preselected volume between upper and lower
fluid levels associated therewith;
a first sensor for sensing the presence of a fluid boundary of
a fluid column at the lower level in said chamber and for sending
a signal indicative thereof;
a second sensor for sensing the presence of a fluid boundary at
the upper level in said chamber and for sending a signal indicative
thereof;
discharge means downstream of said chamber having an outlet and
an inlet coupled to said chamber and to said fluid source;
remotely actuable valve means upstream of said chamber, between
said fluid source and said chamber, said valve means having an outlet
and an inlet coupled to the fluid source and further including means
for opening and closing the valve in response to signals received
from a computer control means;
fluid coupling means coupling the chamber and the discharge means
to the valve outlet;
computer control means coupled to said first and said second sensors
and said valve means, for receiving a signal from said first sensor
indicating the presence of a fluid boundary at the lower level in
said chamber and for sending an opening signal to said valve means
in response thereto so as to initiate filling of said chamber above
said lower level;
operating cycle timer means responsive to said opening signal and
said first sensor signal for measuring an operating time interval
beginning at the opening of said valve and ending upon an ending
signal from said first sensor responding to a fall of fluid level
in said chamber, and said operating cycle timer means including
means for sending a signal corresponding to the operating time interval
to said computer control means;
said computer control means including means responsive to said
second sensor signal indicating the presence of a fluid boundary
at the upper level in said chamber so as to issue a closing command
to the valve, whereupon fluid in said chamber is evacuated, flowing
to said discharge means;
evacuation timer means responsive to said first and said second
sensor signals for measuring a time interval for evacuating said
chamber during which the fluid level in said chamber falls from
said upper level to said lower level and said evacuation timer means
further including means for sending a signal corresponding to the
evacuation time interval; and
said computer control means including first input means for inputting
the preselected volume of the chamber, second input means coupled
to the operating cycle timer means for receiving a signal corresponding
to the operating cycle time interval, third input means coupled
to the evacuation timer means for receiving a signal corresponding
to evacuation time interval, means for calculating a flow rate from
the preselected volume of the chamber and the evacuation time interval
and means for calculating the total volume of the fluid inputted
to said pump from the calculated flow rate and the operating cycle
time interval.
2. The apparatus of claim 1 further comprising means for selectively
displaying the calculated flow rate and the total volume.
3. The apparatus of claim 1 further comprising means responsive
to said ending signal to send an opening signal to said preselected
volume to initiate a second, consecutive metering operation resulting
in the calculation of another total volume.
4. The apparatus of claim 3 further comprising means for storing
the total volume and for adding that total volume to another total
volume upon a repeated operation of said apparatus.
5. The apparatus of claim 3 further comprising inter-cycle time
delay means responsive to said ending signal for delaying a second
operating cycle of said apparatus, responsive to said ending signal
of said first sensor so as to initiate an inter-cycle time delay
so as to delay the sending of an opening signal to said valve means
until expiration of said inter-cycle time delay.
6. The apparatus of claim 1 further comprising valve delay means
for delaying the sending of a closing signal to said valve means
upon receiving a signal from said second sensor means indicating
that the fluid level has been raised to said upper level, so that
said chamber means is filled to a level above said upper level,
and so that said evacuation timer means initiates measuring of said
second time interval when the level of fluid in said chamber means
drops to said upper level.
7. The apparatus of claim 1 further comprising start-up means in
said computer control means for sending an opening signal to said
valve means, and for sending a signal to said operating cycle timer
means so as to initiate a first operating cycle timed interval,
during which said chamber is filled first to said lower level and
then to said upper level so as to initiate a first cycle of said
flow meter operation.
8. The apparatus of claim 1 wherein said fluid coupling means comprises
T-shaped conduit means having three ports connected to said fluid
source, said chamber means and said discharge means, respectively.
9. Apparatus for pumping relatively small metered quantities of
fluid from a fluid source over relatively long periods of time,
comprising:
a chamber defining a preselected volume between upper and lower
fluid levels associated therewith;
a first sensor for sensing the presence of a fluid boundary of
a fluid column at the lower level in said chamber and for sending
a signal indicative thereof;
a second sensor for sensing the presence of a fluid boundary at
the upper level in said chamber and for sending a signal indicative
thereof;
a pump downstream of said chamber and having an inlet and an outlet;
remotely actuable valve means upstream of said chamber, between
said fluid source and said chamber, said valve means having an outlet
and an inlet coupled to the fluid source and further including means
for opening and closing the valve in response to signals received
from a computer control means;
means coupling the chamber and the pump inlet to the valve outlet;
computer control means coupled to said first and said second sensors
and said valve means, for receiving a signal from said first sensor
indicating the presence of a fluid boundary at the lower level in
said chamber and for sending an opening signal to said valve means
in response thereto so as to initiate filling of said chamber above
said lower level;
operating cycle timer means responsive to said opening signal and
said first sensor signal for measuring an operating time interval
beginning at the opening of said valve and ending upon an ending
signal from said first sensor responding to a fall of fluid level
in said chamber, and said operating cycle timer means including
means for sending a signal corresponding to the operating time interval
to said computer control means;
said computer control means including means responsive to said
second sensor signal indicating the presence of a fluid boundary
at the upper level in said chamber so as to issue a closing command
to the valve, whereupon fluid in said chamber is evacuated flowing
to said pump;
evacuation timer means responsive to said first and said second
sensor signals for measuring a time interval for evacuating said
chamber during which the fluid level in said chamber falls from
said upper level to said lower level, and said evacuation timer
means further including means for sending a signal corresponding
to the evacuation time interval; and
said computer control means including first input means for inputting
the preselected volume of the chamber, second input means coupled
to the operating cycle timer means for receiving a signal corresponding
to the operating cycle time interval, third input means coupled
to the evacuation timer means for receiving a signal corresponding
to evacuation time interval, means for calculating a flow rate from
the preselected volume of the chamber and the evacuation time interval
and means for calculating the total volume of the fluid inputted
to said pump from the calculated flow rate and the operating cycle
time interval.
10. The apparatus of claim 9 further comprising means responsive
to said ending signal to send an opening signal to said preselected
volume to initiate a second, consecutive metering operation resulting
in the calculation of another total volume.
11. The apparatus of claim 10 further comprising means for storing
the total volume and for adding that total volume to another total
volume upon a repeated operation of said apparatus.
12. The apparatus of claim 10 further comprising inter-cycle time
delay means responsive to said ending signal for delaying a second
operating cycle of said apparatus, responsive to said ending signal
of said first sensor so as to initiate an inter-cycle time delay
so as to delay the sending of an opening signal to said valve means
until expiration of said inter-cycle time delay.
13. The apparatus of claim 9 further comprising valve delay means
for delaying the sending of a closing signal to said valve means
upon receiving a signal from said second sensor means indicating
that the fluid level has been raised to said upper level, so that
said chamber means is filled to a level above said upper level,
and so that said evacuation timer means initiates measuring of said
second time interval when the level of fluid in said chamber means
drops to said upper level.
14. The apparatus of claim 9 wherein said fluid coupling means
comprises T-shaped conduit means having three ports connected to
said fluid source, said chamber means and said discharge means,
respectively.
15. The apparatus of claim 9 further comprising means for selectively
displaying the calculated flow rate and the total volume.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to flow meters, and in particular
to flow meters for use with positive displacement pumps.
2. Description of the Related Art
Positive displacement pumps are currently being used in a variety
of industrial and other applications. For example, U.S. Pat. No.
4160626 discloses a positive displacement pump of a type useful
for water flooding of oil wells so as to augment the recovery of
oil from producing well. Such pumps may be operated by high pressure
air, natural gas or other fluid pumping media.
Frequently, it is desirable in pumping operations to introduce
one or more chemical additives into the fluid being pumped. Such
additives may, for example, comprise a viscosity enhancer useful
for improving the pumping efficiency. Other additives may, for example,
reduce foaming of the fluid being pumped. Frequently , the use of
such chemical additives is important to maintain the regular operation
of a producing well, and to reduce costly downtime. Many of these
chemical additives are quite expensive, and considerable cost savings
can be realized if overuse of the chemicals is eliminated. An accurate
and reliable metering is needed to insure that the proper amount
of chemical additives are injected, necessary to achieve the desire
objective and to eliminate the usage of additional amounts of these
chemicals beyond the necessary amounts.
In the field of oil production, and in many other commercial fields
of interest today, it is desirable to meter relatively small quantities
of chemical additives, continuously, over a relatively long period
of time. Experience with low flow, high pressure injection systems,
in particular, has indicated the need for improved flow meters.
With regard to flow metering in general, a variety of flow meter
devices have been proposed. For example, a manual sight glass method
employs a sight glass between a source of fluid to be pumped, upstream
of a pump which directs that fluid to its desired destination. A
valve is provided between the source of fluid and the sight glass.
In operation, the pump is energized and the valve is open so as
to allow fluid to fill the sight glass. The sight glass is provided
with two markings, one above the other and the valve is closed when
the level in the sight glass approaches the upper marking. The time
and sight glass level are recorded and level in the sight glass
is allowed to drop to the lower mark, when the time and level are
again recorded. An average flow rate is calculated by dividing the
difference in volume in the sight glass between the two markings,
and the time required for the fluid to drop from the higher mark
to the lower mark in the sight glass.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flow meter
for use with a positive displacement pump.
Another object of the present invention is to provide a flow meter
which can deliver a relatively low flow rate to a variety of low
pressure and high pressure equipment, including high pressure injection
pumps.
Another object of the present invention is to provide flow meters
of the above-described type for use with pumps in which the flow
rate is controlled through timing of the fluid inlet as opposed
to controlling the pump stroke or the pump outlet pressure, for
example.
These and other objects according to the present invention, which
will become apparent from studying the appended description in conjunction
with the drawings, is provided in an apparatus for injecting relatively
small metered quantities of fluid over relatively long periods of
time, comprising:
a fluid source;
a chamber defining a preselected volume between upper and lower
fluid levels associated therewith;
a first sensor for sensing the presence of a fluid boundary of
a fluid column at the lower level in the chamber and for sending
a signal indicative thereof;
a second sensor for sensing the presence of a fluid boundary at
the upper level in the chamber and for sending a signal indicative
thereof;
discharge means downstream of the chamber having an outlet and
an inlet coupled to the chamber and to the fluid source;
remotely actuable valve means upstream of the chamber, between
the fluid source and the chamber, the valve means having an outlet
and an inlet coupled to the fluid source and further including means
for opening and closing the valve in response to signals received
from a computer control means;
fluid coupling means coupling the chamber and the discharge means
to the valve outlet;
computer control means coupled to the first and the second sensors
and the valve means, for receiving a signal from the first sensor
indicating the presence of a fluid boundary at the lower level in
the chamber and for sending an opening signal to the valve means
in response thereto so as to initiate filling of the chamber above
the lower level;
operating cycle timer means responsive to the opening signal and
the first sensor signal for measuring an operating time interval
beginning at the opening of the valve and ending upon an ending
signal from the first sensor responding to a fall of fluid level
in the chamber, and the operating cycle timer means including means
for sending a signal corresponding to the operating time interval
to the computer control means;
the computer control means including means responsive to the second
sensor signal indicating the presence of a fluid boundary at the
upper level in the chamber so as to issue a closing command to the
valve, whereupon fluid in the chamber is evacuated, flowing to the
discharge means;
evacuation timer means responsive to the first and the second sensor
signals for measuring a time interval for evacuating the chamber
during which the fluid level in the chamber falls from the upper
level to the lower level and the evacuation timer means further
including means for sending a signal corresponding to the evacuation
time interval; and
the computer control means including first input means for inputting
the preselected volume of the chamber, second input means coupled
to the operating cycle timer means for receiving a signal corresponding
to the operating cycle time interval, third input means coupled
to the evacuation timer means for receiving a signal corresponding
to evacuation time interval, means for calculating a flow rate from
the preselected volume of the chamber and the evacuation time interval
and means for calculating the total volume of the fluid inputted
to the pump from the calculated flow rate and the operating cycle
time interval.
The apparatus is particularly advantageous when used with positive
displacement pump discharge means.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, wherein like elements are referenced alike:
FIG. 1 is a perspective view of a pumping system including a flow
meter according to principles of the present invention;
FIG. 2 is a schematic diagram of the system of FIG. 1;
FIG. 3 is a front elevational view of the flow meter and valve
components of the system of the preceding FIGURES;
FIG. 4 is a top plan view of the flow meter and valve of FIG. 3;
FIG. 5 is an enlarged, partly schematic elevational view of the
flow meter of FIG. 3;
FIG. 6 is an enlarged fragmentary view of FIG. 3 showing the vertical
body portion thereof, taken in cross-section;
FIG. 7 is an end view of the column of FIG. 6;
FIG. 8 is a fragmentary view of the lower central portion of FIG.
6 shown on an enlarged scale; and
FIGS. 9a and 9b, taken together, comprise a flow diagram illustrating
operation of a flow meter according to principles of the present
invention .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and initially to FIG. 1 a pumping
system is generally indicated at 10. The system includes a fluid
source 12 coupled by a conduit 14 to a pump 16. Pump 16 includes
an inlet 18 connected to conduit 14 and an outlet 20 (see FIG. 2).
Pump 16 is a reciprocating positive displacement pump described
in commonly assigned U.S. Pat. No. 4160626 which is herein incorporated
by reference.
A T-junction 24 is disposed in conduit 14 and provides a tap for
fluid connection to a flow meter generally indicated at 26. Flow
meter 26 includes a vertical, generally tubular float chamber 28
connected at one end to T-junction 24 and having a vent line 30
at its upper end. A control cabinet 66 is disposed atop float chamber
28. As will be explained in greater detail herein, control cabinet
66 includes a computer having controllable timing and switching
functions to meter the flow rate and total volume of fluid inputted
to pump 16 along conduit 15.
Also shown in FIG. 1 is a solenoid valve 36 disposed in conduit
14 upstream of the flow meter and pump so as to make and break fluid
flow connection thereto. With solenoid valve 36 in a closed position,
fluid source 12 is isolated from equipment downstream of the valve.
With the valve in an open position, fluid from source 12 travels
along conduit 14 in a flow which is split at T-junction 24 into
a first path via conduit 15 directed to pump 16 and a second path
via float chamber 28 directed toward flow meter 26. A solenoid control
unit 38 is mounted atop valve 36 and provides remote actuation of
the valve in response to signals transmitted along a control cable
40 which interconnects the flow meter to the solenoid actuator
of the valve.
FIG. 2 is a schematic diagram of the pumping system 10. The float
chamber 28 is shown therein being partially filled with a fluid
44 having an upper fluid boundary 46. A float 50 rides on the fluid
column 44 at the fluid boundary 46 thereon. The float 50 is also
illustrated in phantom at a raised position adjacent the top of
float chamber 28.
The numeral 54 generally indicated a computer having multiple timing
functions or timing a number of different operating intervals, along
with calculation means for calculating flow rate, total volume,
and further has valve and pump controls, temperature compensation
and other functions. The computer of the preferred embodiment preferably
comprises an Hitachi MCU/MPU device of the HD6305 microcomputer
family.
As will be explained in greater detail herein, the preferred embodiment
of the flow meter is incorporated in a pumping system, although
it will become apparent to those skilled in the art that the flowmeter
can also be used with other equipment, including low pressure and
even gravity-fed fluid distribution systems. Referring again to
the pumping system 10 when pump 16 is activated, fluid fed to its
input 18 is directed to a discharge conduit 60 which, for example,
may comprise a downhole of a well.
Briefly, in general terms, valve 36 is opened for a measured time
interval to initiate flow meter operation. Over a first portion
of the interval, flow along conduit 14 is split in a first flow
path filling float chamber 28 and in a second flow path directed
toward pump inlet 18. The first portion of the time interval continues
until the float chamber is filled to an upper operating level. Thereafter,
in the second portion of the time interval, solenoid valve 36 is
closed, stopping flow from the valve output to the pump inlet. However,
the float chamber 28 is filled with fluid which is allowed to drain
into or otherwise be evacuated into the downstream discharge means.
Since the discharge means herein comprises a positive displacement
pump, and since conduit 14 is closed by valve 36 the fluid in chamber
28 is sucked through conduit 15 into pump inlet 18 with a negative
pressure induced by pump action. Over a second portion of the time
interval, the fluid level is allowed to fall in float chamber 28
for a measured period Of time over which a known volume reduction
in float chamber 28 occurs. After the volume reduction, the time
interval is terminated, preferably by de-energizing pump 16 via
control signals carried along a control line 62 leading from computer
54 to the pump.
Given the known volume reduction, and the measured time interval
over which the volume reduction occurs, the flow rate through pump
16 for the second portion of the overall time interval, is accurately
estimated, assuming a constant flow rate, and the first portion
of the time interval is used to calculate the total volume discharged
by pump 16 throughout the entire operating cycle. According to one
aspect of the present invention, a surprisingly accurate match between
the flow rates of the first and second portions of the time interval
was experienced. The accurate match was also verified with mathematical
error analysis which showed an unexpected overall accuracy in the
fluid metering system.
Referring now to FIG. 3 flow meter 26 includes a cabinet 66 in
which the computer and control circuitry associated therewith are
stored. The computer 54 includes a display 68 indicating various
operating conditions and parameters. A selector switch 94 causes
the display 68 to read either the total volume discharged by pump
16 since the beginning of an operating period, or can be switched
to display the total elapsed time of the operating period. In addition,
cabinet 66 includes an indicator light for indicating a reset or
an erroneous operating condition. For example, float chamber 28
is expected to fill within a known predetermined time after opening
valve 36. If the switches 80 82 do not detect the presence of a
fluid in float chamber 28 within that known time, an indicator
light is illuminated, informing an operator that system maintenance
is required. For example, the fluid source 12 may have become depleted
during the operating period. The display 68 normally displays the
current flow rate, with switch 94 providing optional readouts of
total volume pumped since powerup of the flow meter system, and
total elapsed time since powerup of the flow meter system. The reset
button 92 restarts the computer 54 and its associated control circuitry
to begin another flow meter operating period, with total volume
and elapsed time being reset to zero. Lamp 94 is illuminated if
the flow rate is two low or if a malfunction is sensed by the computer.
Valve 36 as mentioned above, has a solenoid actuator 38 connected
to the computer by a control cable 40. Electrical power for operating
the solenoid 38 is provided by a supply line 65 having a plug 67
for conventional connection to an electrical source, not shown.
Referring additionally to FIG. 5 the float float chamber 28 of
flow meter 26 includes a generally cylindrical housing 70 which
is terminated at its lower end to T-junction 24 in flow communication
with conduit 14 and the conduit 15 connecting the T-junction to
the inlet 18 of pump 16. Disposed within housing 70 is an internal
tubular instrument housing 72 having an interior 74 which preferably
is maintained in a dry condition, separated from the fluid flowing
through the pumping system. Disposed within interior of housing
72 are lower and upper switches 80 82 which preferably are of
the magnetically actuable type.
A float 84 rides on the upper boundary of the fluid column disposed
within housing 70. The fluid column rise within the float chamber
through a series of apertures 88 formed in a lower disk-like support
plate 90 as will be explained with reference to FIG. 7. Float 84
preferably carries a magnetic field which operates switches 80
82 when disposed immediately adjacent thereto. The switches 80
82 are schematically illustrated in FIG. 5 in a much larger scale
than the surrounding components. However, FIG. 5 is useful for explaining
the operation of the flow meter, as will be seen shortly.
Referring now to FIGS. 6-8 float chamber 28 will be described
in greater detail. Float chamber 28 preferably comprises a float
housing made from a conventional metallic pipe which comprises the
aforementioned tubular housing 70. The upper and lower ends of the
pipe are threaded, the lower end for connection to the T-junction
24 and the upper end for connection to cabinet 66. A bushing 98
is welded at the upper end of housing 70 to prevent the intrusion
of fluid into cabinet 66 and the electronics stored therein. A threaded
outlet port is provided at 100 for vent line 30.
The float 84 is preferably cylindrical in configuration having
an inner bore 85 for sliding along the inner tublike housing 72.
The lower end of tubular housing 70 is enclosed by baffle disk 90
having a series of accurately dimensioned apertures 88 permitting
flow into and out of float chamber 28. Referring additionally to
FIG. 8 the inner tubular housing 72 is enclosed at its lower end
by a threaded rod 104 to maintain the interior of the housing in
a dry condition. The threaded rod 104 provides convenient mounting
of baffle disk 90 as illustrated in FIGS. 6 and 7 wherein the
threaded rod 104 is received in a central aperture in the disk-like
baffle plate 90. The baffle disk 90 may be readily removed from
the flow meter apparatus, permitting a ready exchange of the baffle
plate for a plate having a different number or size apertures, thus
providing different calibrations for the flow meter as required.
The float 84 and the switches 8082 disposed within interior tubular
housing 72 cooperate, as described above, for switch operation as
the float travels therepast, in response to a changing fluid level
within float chamber 28. In the preferred embodiment, the float
is of the magnetic type, and is commercially available as a vertically
mounted TELLEVEL Model No. 505 available from the Revere Corporation
of America. The switches 8082 may comprise, for example, magnetically
operated reed switches. The switches 8082 are spaced apart, being
positioned at selected locations within the inner tubular housing
72. As indicated schematically in FIG. 5 it is generally preferred
that the switches 8084 be spaced inwardly of the operating end
points of column 28. That is, it is preferred that the lower switch
80 be positioned above baffle disk 90 and the upper switch 82 be
positioned slightly below the outlet 100 for vent line 30. This
construction allows the preferred operating conditions wherein the
fluid level can rise above the upper switch 82.
According to one aspect of the present invention, the switches
8082 are positioned such that corresponding fluid levels of a fluid
column disposed within cylindrical housing 70 are spaced a known
distance apart so as to define an accurately determined volume therebetween.
The switches 8082 are located exactly at the two defined fluid
levels to provide accurate timing of the fall of a fluid column
from the upper level at switch 82 to the lower level at switch
80. It is generally preferred that switch 80 be located above baffle
disk 90 so that, when the fluid column drops to the lower switch
80 control circuitry associated with the switch can discontinue
pump operation, leaving an amount of fluid in float chamber 28 prior
to initiation of a consecutive operating cycle. This feature, along
with other features shown and described herein, contribute to a
heretofore unavailable convenient and rapid flow measurement having
an improved, low error rate.
With reference to FIGS. 9a,9b an initial cycle of operation is
begun with fluid source 12 installed, and the valve 36 opened to
filling that portion of conduit 14 coupling the fluid source 12
to the solenoid valve 36. The computer 54 initiates the first cycle
of operation by sending an opening signal along cable 40 to the
solenoid actuator 38 opening valve 36 and allowing the remaining
portion of conduit 14 float chamber 28 and conduit 15 to become
filled with fluid 44. As mentioned above, flow continues along conduit
14 being split at T-junction 24 with a first portion of the fluid
flow being discharged by pump 16 and a second portion of the fluid
flow filling float chamber 28.
As fluid enters float chamber 28 it reaches the lower level defining
the bottom boundary of the preselected volume, tripping switching
80. As indicated schematically in FIG. 5 switch 80 (and switch
82 also) is connected through electrical conductors to the computer
54 within housing 66. No control action is taken with the first
operation of switch 80. Fluid continues to enter float chamber 28
raising float 84 above the lower control level. Float 84 is raised
to a point adjacent switch 82 and when the fluid level reaches the
upper level setting, that level defining the upper boundary of the
preselected measured volume, switch 82 is tripped. Again, the control
action is taken with the first operation of switch 82. If desired,
computer 54 can be programmed so as to acknowledge the initial tripping
of switches 8082 to indicate a satisfactory precursor to the first
metering event.
According to one aspect of the present invention, the fluid is
allowed to rise within float chamber 28 above the upper level of
the measured volume within the float chamber. This amount of "overshoot"
above the upper level of switch 82 is not critical, for reasons
which will be made clear herein. In the preferred embodiment, the
amount of "overshoot" within float chamber 28 is defined
by a time delay stored within computer 54 and initiated when the
upper switch 82 is tripped. After expiration of the "overshoot"
time delay, computer 54 sends a closing signal to solenoid 38 along
cable 40 instructing valve 36 to close. As mentioned above, a portion
of the fluid flow in conduit 14 is discharged directly to pump 16
and, for the time being, passes through the pumping system without
direct measurement thereof. With the closing of solenoid 36 this
flow is terminated.
It is generally preferred that the fluid source 12 have a positive
pressure head to maintain a steady, but as yet unmetered, flow rate
through conduits 1415 and float chamber 28. In the preferred embodiment,
the fluid source 12 provided sixteen inches of head to the solenoid
valve 24. With valve 36 in a closed position flow is continued through
pump 16 as the column of fluid within float chamber 28 is allowed
to fall. The column falls from its initial maximum undefined height
with float 84 falling past upper switch 82 which is tripped as the
fluid column reaches the defined upper boundary of the measured
volume within float chamber 28. This latter operation of switch
82 initiates an evacuation time interval measurement within computer
54. The fluid within float chamber 28 continues to fall, until float
84 initiates tripping of the lower switch 80. The later operation
of switch 80 initiates a number of different responses in the control
system. For example, the first, overall time interval (operating
interval) begun when valve 36 is initially opened, is terminated.
Next, the shorter time interval (the evacuation time interval) begun
when the fluid column falls past the upper level associated with
switch 82 is also terminated. Third, it is generally preferred
that pump 16 be deenergized to prevent further falling of the fluid
column with float chamber 28. Finally, an inter-cycle time delay
is initiated, the purpose of which will be described herein shortly.
The data collected by computer 54 during the operating cycle is
as follows. As mentioned above, the volume within float chamber
28 between the levels associated with upper switch 82 and lower
switch 80 is accurately measured. This quantity is input into the
memory of computer 54. As the fluid column falls in float chamber
28 the interval of its falling between upper switch 82 and lower
switch 80 is accurately timed by operation of those switches. Computer
54 divides the known measured evacuation volume by the measured
time interval to discharge the volume and calculates an average
flow rate present in the float chamber as the fluid column falls
between the levels associated with switches 8082.
According to other aspects of the present invention, the pumping
system and in particular the flow meter apparatus are constructed
such that the flow rate through pump 16 is maintained constant,
regardless of whether the flow thereto comes from fluid source 12
or the falling fluid column within float chamber 28.
The overall pumping cycle (operating cycle) is accurately measured
by computer 54 beginning at the point in time when valve 36 is
opened, and ending when the fluid column falls to the level associated
with lower switch 80 tripping that switch. As mentioned, at the
point in time when switch 80 is tripped at the end of a pumping
cycle, pump 16 is deactivated to prevent any unmeasured loss of
fluid in the pumping system. Since the flow rate through pump 16
is held constant at all times, the average flow rate calculated
by the falling fluid column within float chamber 28 can be readily
applied to the overall pumping cycle and thus the total volume passing
through pump 16 from the time valve 36 is initially opened, until
the time that the falling column trips switch 80 can be very accurately
determined.
The flow meter according to the present invention finds particular
application with relatively low pumping rates occurring over relatively
long or extended time intervals. As mentioned above, it is frequently
desirable in pumping, and other commercial applications that a slow
steady discharge be maintained throughout a prolonged work period.
In particular, a flow meter instructed according to principles of
the present invention is found to provide very accurate metering
over flow rates ranging from one or more pints per day to twenty
gallons per hour or more. The accuracy of the flow meter has been
found to be consistently below 5%.
It is generally preferred in the commercial embodiment of the present
invention that a third float-activated switch be installed between
the first and second switches so as to define a smaller, but accurately
measured float chamber volume. An operator can select among two
different upper limit switches with electrical controls installed
within cabinet 66. In the preferred embodiment, the pipe for tubular
housing 70 had diameters ranging between one and three inches. The
first upper limit switch was placed approximately one inch above
the lower limit switch, while the second upper limit switch was
placed six inches above the lower limit switch.
The preferred embodiment according to the present invention also
includes temperature measuring devices within conduit 14 of the
type providing a digital temperature signal to computer 54. The
preferred temperature range of operation is between 32 and approximately
160.degree. F. Computer 54 was programmed for conventional temperature
compensation calculations based upon a known reference temperature
at which the pumping system is initially calibrated, when the switches
within float chamber 28 are spaced apart to attain a well defined,
accurately measured test volume.
Upon subsequent operations of the flow meter, an opening signal
is sent to valve 36 raising the fluid level in float chamber 28
from the lower level associated with switch 80 to a point above
the upper level associated with switch 82 the operation of switch
82 associated with an upwardly rising column initiating the overshoot
time delay referred to above, typically on the order of one or two
seconds. At the end of the overshoot time delay, a closing signal
is sent to solenoid 36 whereupon all fluid flowing through pump
16 is associated with the falling fluid column within float chamber
28. As before, the time interval required for the fluid column to
fall between switches 8082 is accurately measured to determine
the average flow rate over that period. When bottom switch 80 is
tripped by a falling fluid column, the timing cycle is terminated,
pump 16 is deactivated and any optional inter-cycle time delay is
initiated. Computer 54 calculates the average flow rate during falling
of the fluid column between switches 8082 and applies flow rate
to the overall time period begun when valve 36 is opened and ending
when switch 80 is tripped by a falling fluid column.
As mentioned above, optional an inter-cycle time delay may be provided.
This time delay is useful for very low flow rates. Although the
fluid of source 12 will not be continuously fed to pump 16 fluid
pulses corresponding to the total volume passed during the above-described
metering operation can be spaced throughout an operating period
by simply spacing apart the metering operations with a known inter-cycle
time delay. For example, assuming that a metering event as described
above allows the passage of a total volume of one pint, and the
metering event occurs over one minute, the inter-cycle time delay
can be set at fifty-nine minutes to provide an effective, average
flow rate of one pint per hour. In practice, if extremely low flow
rates are of principal concern, the size of conduit 14 float chamber
28 and conduit 15 can be reduced for smaller total volume quantities
associated with a metering event, permitting the inter-cycle time
delay to be significantly reduced, to thereby approximate a more
nearly continuous dispensing of injected fluid into discharge conduit
60.
In summary, it will now be appreciated that the flow meter is connected
to a positive head of fluid in order to charge and recharge the
volume float chamber 28. The volume float chamber is also connected
to the suction side of a discharge device, such as pump 16. A metering
cycle starts with the volume float chamber being opened to the liquid
source, with solenoid 36 being actuated by an opening signal sent
to it from the control computer 54. Assuming an operation subsequent
to initial start-up, the opening signal to the valve can be sent
in response to the float falling to the lower position, tripping
switch 80. That is, an inter-cycle time delay is not required for
flow meter operation. As the volume float chamber 28 fills, the
float 84 rises until a second signal is received in computer 54
upon operation of switch 82. The valve can either be closed upon
the occurrence of this signal, or it can continue during an overshoot
time delay. Assuming the solenoid valve is closed when switch 82
is activated, the pump is caused to draw fluid from the float chamber
28 only. The time required to partially evacuate the proctological
volume of float chamber 28 is measured by the timing circuit within
computer 54. The partial evacuation time and the proctological volume
are converted into a flow rate which is displayed by display 68.
At this point in time, the low fluid level signal from switch 80
again opens the solenoid valve 36 and the flow meter cycle repeats.
Use of a magnetic float and magnetic sensors allows float chamber
28 to be effectively shortened--an important feature where a customer's
space allocations for the flow meter are limited. However, other
level sensing instrumentation can be employed. For example, an optical
system may be installed wherein the float breaks a light path passing
through float chamber 28 at carefully defined levels. As another
example, if the fluid being metered is electrically conductive,
electrodes can be placed along float chamber 28 and resistance
measuring a circuitry can indicate the passage of a fluid boundary
past the electrodes.
Obviously, any modifications and variations of the present invention
are possible in light of the above teachings. Thus, it is to be
understood that, within the scope of the appended claims, the invention
may be practiced otherwise than as specifically described above.
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