Note: Descriptions are shown in the official language in which they were submitted.
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LIQUID LEVEL MEASUREMENT DEVICE AND INSTALLATION
INCORPORATING THE SAME
Field of the Invention
[0001] The present invention relates generally to measuring devices
and in
particular, to a liquid level measurement device and an installation
incorporating the
same.
Backuound of the Invention
[0002] Systems to disperse or treat household wastewater, sewage,
stormwater
and the like (hereinafter referred to as "wastewater") are well known in the
art. For
example, one conventional system for disposing with or dispersing wastewater
comprises a septic tank receiving wastewater from the structure serviced by
the
treatment system, a distribution box receiving effluent from the septic tank
and a
subsurface absorption field receiving the effluent distributed by the
distribution box.
Alternatively, the treatment system may omit the distribution box and simply
comprise a septic tank delivering effluent directly to the absorption field or
may
replace the distribution box with a pump or siphon that doses the absorption
field with
effluent from the septic tank.
[0003] The absorption field may be for example a gravel trench
installation
comprising an underground layer of crushed stone, gravel, synthetic material
and/or
other suitable material that creates an underground distribution trench or bed
for
effluent or water. An upper layer of cover or backfill material is disposed
over the
trench or bed and extends to finished grade. Alternatively, the absorption
field may
be a leaching chamber installation comprising an underground pre-fabricated
leaching
chamber or similar structure that creates an underground passageway for
effluent or
water. Similarly, a layer of cover or backfill material is disposed over the
leaching
chamber and extends to finished grade. Inspection ports or observation tubes
(collectively referred to herein as "inspection ports") are sometimes provided
in the
installations described above to enable the liquid level therein to be
monitored. Each
inspection port typically comprises a cylindrical tube having a diameter in
the range
of from about three (3) inches to six (6) inches that extends deep enough into
the
installation to enable the liquid level therein to be measured. Holes are
usually
provided in the lower portion of the cylindrical tube to allow liquid
accumulating in
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the absorption field to enter the inspection port so that the liquid level in
the
inspection port corresponds to the liquid level in the absorption field. A
removable
cap or plug overlies the cylindrical tube to seal the same when liquid level
measurements are not being made. The cap or plug is typically positioned at or
above
the finished grade so that the liquid level in the installation can be checked
without
digging. In some instances however, owners of these installations bury the
caps or
plugs typically for aesthetic reasons. This of course makes checking the
liquid levels
more difficult and time consuming.
[0004] As will be appreciated, being able to monitor the liquid level
in septic
or stormwater absorption fields is important for a number of reasons. In
particular,
being able to monitor the liquid level in such an absorption field allows the
capacity
of the absorption field to be evaluated, allows the owner/operator to detect
when the
absorption field is reaching its ultimate capacity and allows the
owner/operator to be
alerted before the absorption field becomes overloaded. Overloading of the
absorption field is of particular importance as it may result in wastewater or
effluent
backing up into the structure it services and/or wastewater or effluent
breaking out
onto the ground surface. Both of these conditions have serious negative public
health
and environmental impacts due to the possible presence of bacteria in the
wastewater
or effluent.
[0005] In the past, liquid levels in absorption fields have been measured
by
inserting a measuring stick or other object into the inspection port, removing
the
measuring stick from the inspection port and visually examining the measuring
stick
to determine how much of the measuring stick is wet. As will be appreciated,
measuring liquid levels in this manner is time consuming, cumbersome and only
provides liquid level measurements at snapshots in time.
[0006] Mechanical (i.e. mercury) float switches have also been used
to sense
liquid levels in absorption fields. Unfortunately, these float switches
require large
diameter tubes to provide for the minimum cord length required in order for
the float
to travel up and down. Also if different liquid levels are to be sensed, a
separate float
switch for each liquid level to be sensed is required. Furthermore, as the
float
switches are in direct contact with the wastewater or effluent, the float
switches are
prone to fouling as a result of biological matter buildup on the float
switches.
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[0007] Pressure transducers which sense liquid levels by detecting
the change
in liquid pressure acting on the pressure transducers have also been
considered. As
with mechanical float switches, these pressure transducers are also prone to
fouling as
a result of biological matter buildup on the pressure transducers. To avoid
this
problem, pressure transducers that detect the change in the air pressure in
the
underground trench, bed or leaching chamber bed as the liquid level therein
changes
have been used. Unfortunately these pressure transducers tend to produce
unreliable
results once air pressures dissipate and equalize.
[0008] Use of ultrasound sensors in sewer manholes and storm drains
has also
been considered. For example, U.S. Patent No. 7,002,481 to Crane et al.
discloses a
monitoring system including one or more monitoring devices, positioned in
sewer
manholes, storm drain manholes or catch basins, etc., and a remote monitoring
station
that communicates wirelessly with the monitoring devices. Each monitoring
device
comprises sensors, a two-way telemetry unit, a power supply, a processor and
supporting hardware, all located in an enclosed, waterproof housing. Each
monitoring
device is placed within a manhole cavity to obtain depth (e.g., water level)
measurements and report the measurements back to the remote monitoring
station,
which analyzes the data and responds to alert messages when a dangerous water
level
is detected. The sample and reporting rates of the monitoring devices, as well
as the
water level threshold values, may be remotely programmable via commands
transmitted from the remote monitoring station. An additional sensor may
monitor
the manhole cover for security purposes.
[0009] In addition to monitoring the liquid level in absorption
fields and the
like, monitoring the liquid level in groundwater wells and other types of
wells is also
important to detect situations where well levels rise to the point where the
levels may
interfere with the operation of sewer disposal systems or where bacteria
and/or viruses
present in the liquid may reach the groundwater table and cause contamination.
[00010] Although liquid level sensors are known, there exists a need
for a
reliable non-contact, liquid level measurement device suitable for use in
installations
comprising narrow diameter pipes extending into the liquid whose level is to
be
monitored. It is therefore an object of the present invention to provide a
novel non-
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contact, liquid level measurement device and to an installation incorporating
the
same.
Summary of the Invention
[0001] Accordingly, in one aspect there is provided a liquid level
measurement device comprising: a hollow seamless pipe defining an interior
passage
for insertion into an installation in which a liquid level is to be monitored;
a non-
contact sensor assembly disposed within said pipe adjacent an upper end
thereof at a
location spaced above the liquid, said sensor assembly sensing the level of
said liquid
and generating output representative of said liquid level, wherein the
interior surface
of said pipe at least between the liquid and said sensor assembly is
continuous and
uninterrupted and free of inwardly extending projections so that said interior
passage
is unobstructed; and at least one air relief passageway communicating with the
interior of said pipe adjacent said sensor assembly.
[0002] In one embodiment, the sensor assembly is an ultrasound sensor
assembly. The ultrasound sensor assembly is configured to transmit an
ultrasound
energy wave down the mounting pipe and to receive the return ultrasound energy
wave reflected by the surface of the liquid. The sensor assembly is configured
to
measure the time taken for the transmitted ultrasound energy wave to travel to
the
surface of the liquid and reflect back to the sensor assembly thereby to sense
the
liquid level. If desired, the measured time taken may be adjusted to
compensate for
the density of the air by measuring the ambient temperature and/or humidity
levels.
[0003] The liquid level measurement device may further comprise a
communications interface configured to transmit the output to a remote unit.
In one
embodiment, the communications interface is a wired communications interface.
In
another embodiment, the communications interface is a wireless communications
interface
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[0004] If desired, a mechanical backup sensor, such as for example a
mechanical float or magnetic reed switch, may be included in the liquid level
measurement device.
[0005] According to another aspect there is provided an installation
comprising: an underground region containing liquid; at least one narrow
diameter,
hollow seamless pipe defining an interior passage extending into said region;
a non-
contact liquid level measurement device disposed within said pipe adjacent an
upper
end thereof, said liquid level measurement device configured to measure the
liquid
level in said region, wherein the interior surface of said pipe at least
between the
liquid in said region and said liquid level measurement device is continuous
and
uninterrupted and free of inwardly extending projections so that said interior
passage
is unobstructed; and at least one air relief passageway communicating with the
interior of said pipe adjacent said liquid level measurement device.
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[00016] The liquid level measurement device is positioned within the
pipe in a
manner to inhibit interference. The liquid level measurement device is also
positioned so that it typically remains spaced from liquid in the region.
[00017] The liquid level measurement device allows the liquid level of
an
installation such as for example, an absorption field, groundwater well or the
like, to
be monitored quickly and easily on a regular basis allowing an alarm condition
to be
signaled should a high liquid level occur that exceeds a threshold level. In
this
manner, the owner/operator can be alerted to the high liquid level condition
allowing
the owner/operator to take remedial action if appropriate. The liquid level
measurement device also allows historical liquid level data to be logged. In
the case
of absorption fields, the historical liquid level data can be used to plan the
distribution
of effluent to different trenches or beds and/or to determine if and when the
absorption field needs to be expanded. In the case of groundwater level
monitoring,
historical data concerning groundwater levels can be maintained and provided
to
regulatory agencies if required. Also, as the liquid level measurement device
employs
a non-contact sensor, cross-contamination of groundwater from bacteria or
viruses
which may be present on the liquid level measurement device is avoided.
Brief Description of the Drawings
[00018] Embodiments will now be described more fully with reference to the
accompanying drawings in which:
[00019] Figure 1 is a side elevational view, in section, of a liquid
level
measurement device;
[00020] Figure 2 is a sectional view of the liquid level measurement
device of
Figure 1 taken along line 2-2;
[00021] Figure 3 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1 installed in an existing inspection port of a
gravel
trench installation;
[00022] Figure 4 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1, installed in a new or retrofit inspection port
of
another gravel trench installation;
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[00023] Figure 5 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1 installed in the inspection port of a leaching
chamber
installation; and
[00024] Figure 6 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1, installed in the inspection port of another
leaching
chamber installation;
100025] Figure 7 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1, installed in a groundwater well; and
[00026] Figure 8 is a side elevational view, in section, of the liquid
level
measurement device of Figure 1, installed in a "flush mount" groundwater well.
Detailed Description of the Embodiments
[00027] Turning now to Figures 1 and 2, a liquid level measurement
(LLM)
device designed to determine the distance to or height (some referred to as
"ponding
level") of a liquid within an installation such as for example, an absorption
field,
groundwater well or other well, subsurface wastewater, septic or stormwater
distribution trench or bed or the like, is shown and is generally identified
by reference
numeral 10. In this embodiment, the LLM 10 is to be inserted into an
inspection port
of an absorption field or the like and to sense the liquid level therein. As
can be seen,
LLM device 10 comprises a sensor assembly 12 mounted on a circuit board 14
disposed within an inner plastic sleeve 16. The circuit board 14 is suspended
from a
cap 17 at the top of the inner sleeve 16. An outer sleeve 18 is pressed onto
and
surrounds the upper portion of the inner sleeve 16. The interior wall of the
outer
sleeve 18 adjacent its upper end is threaded and receives a cap 20. Cap 20
comprises
a threaded shank 20a that engages the threaded interior of the outer sleeve
18.
[00028] A mounting pipe 22 receives the lower portion of the inner
sleeve 16.
The diameter of the mounting pipe 22 is such that the top end 22a thereof
abuts the
bottom end of the outer sleeve 18. In this manner, the sensor assembly 12 is
accurately positioned in the mounting pipe 22. The mounting pipe 22 is
continuous
and thus, is free of joints, seams or the like. The length of the mounting
pipe 22 is
selected so that the mounting pipe rests at the bottom of the absorption
field. Holes
22a are provided in the lower portion of the mounting pipe 22 so that liquid
entering
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the inspection port also enters the mounting pipe. In this manner, the liquid
level in
the mounting pipe 22 corresponds to the liquid level in the absorption field.
[00029] Air relief channels 24 are formed in the outer surface of the
inner
sleeve 16 and communicate with air relief slots 26 formed in the bottom end of
the
outer sleeve 18.
[00030] Sensor assembly 12 comprises a microcontroller 40
communicating
with a transmit ultrasound transducer 42 via a transmit amplifier 44 and with
a receive
ultrasound transducer 46 via a receive amplifier 48. Microcontroller 40 also
communicates with a thermistor or other temperature sensor (not shown) and a
remote
control unit (not shown) via a communications interface 52 such as for example
an
RS-485 wired interface. A switching regulator 54 is also provided on the
circuit
board 14 and provides appropriate regulated power to the components of the
sensor
assembly 12. The switching regulator 54 and the communications interface 52
are
coupled to a terminal block 56 adjacent the top of the circuit board 14. The
terminal
block 56 receives the conductors extending from the LLM device power source
and
conductors from the remote control unit.
[00031] The circuit board 14 and the sensor assembly 12 are sealed
within the
inner sleeve 16 with the exception of the ultrasound transducers 42 and 46,
which
protrude from the sealed bottom of the inner sleeve. As the ultrasound
transducers 42
and 46 are exposed, weather proof ultrasound transducers are used.
[00032] The remote control unit may be an interface to an alarm panel,
a relay
contact output, a liquid crystal display (LCD) or a light emitting diode (LED)
level
meter. The remote control unit calculates the liquid level in the absorption
field based
on data received from the LLM device 10 and signals an alarm condition if a
high
liquid level is detected in the absorption field that exceeds a threshold
level. The
remote control unit also maintains a historical log of liquid level data that
can be used
to plan the distribution of effluent to different trenches or beds and/or to
determine if
and when the absorption field needs to be expanded. If the remote control unit
includes a display, the sensed liquid level and/or historical liquid level
data may be
displayed.
[00033] In use, the LLM device 10 is inserted into the inspection port
of an
absorption field for dispersing wastewater or stormwater. The length of the
mounting
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pipe 22 is selected so that the mounting pipe rests at the bottom of the
absorption field
while positioning the sensor assembly 12 near the top of the inspection port.
In this
manner, the sensor assembly 12 remains safely spaced from liquid accumulating
in
the absorption field. In operation, the microcontroller 40 generates an
ultrasonic
frequency pulse at intervals and applies each pulse to the transmit amplifier
44. The
transmit amplifier 44 in turn amplifies the pulse and conveys the pulse to the
transmit
ultrasound transducer 42. The transmit ultrasound transducer 42 in response,
transmits an ultrasound energy wave that travels down the mounting pipe 22.
100034] When the transmitted ultrasound energy wave encounters the
surface
of the liquid within the mounting pipe 22, the ultrasound energy wave is
reflected and
thus, travels back up the mounting pipe 22 towards the LLM device 10. When the
reflected ultrasound energy wave reaches the LLM device 10, the ultrasound
energy
wave is detected by the receive ultrasound transducer 46. The receive
ultrasound
transducer 46 in response generates an electronic signal that is conveyed to
the
receive amplifier 48. The receive amplifier 48 amplifies the received signal
and
verifies that the received signal is the same ultrasonic frequency as the
transmitted
signal. The amplified and verified signal is then conveyed to the
microcontroller 40.
The microcontroller 40 in turn calculates how long it took the ultrasound
energy wave
to travel from the LLM device 10 to the surface of the liquid in the mounting
pipe 22
and back. The calculated "round trip" time in milliseconds is adjusted by the
microcontroller 40 using a zero liquid level measurement that is obtained
during
calibration of the LLM device 10. The microcontroller 40 also takes a
temperature
reading from the thermistor and conveys the adjusted "round trip" time and
temperature reading to the communications interface 52. The communications
interface 52 in turn transmits the adjusted round trip time and temperature
reading to
the remote control unit via the terminal block 56.
[00035] The remote control unit in response, uses the adjusted round
trip time
and temperature reading to calculate accurately the liquid level or total
depth of the
liquid in the installation and determine if a high liquid level condition that
exceeds the
threshold level exists. As will be appreciated, as the speed of sound in air
varies
according to temperature, the temperature reading allows the remote control
unit to
calculate accurately the liquid level. If a high liquid level condition
exceeding the
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threshold level exists, the remote control unit signals an alarm condition.
The
signaled alarm condition may be for example an audio alarm, a visual alarm,
and/or a
networked notification such as an email message or other TCP/IP, modbus or
similar
protocol notification. In this manner, the owner/operator is alerted to the
high liquid
level condition allowing the owner/operator to take remedial action if
appropriate.
[00036] As the mounting pipe 22 is free of joints, seams or the like,
the
transmitted and reflected ultrasound energy waves are able to travel within
the
mounting pipe with little, if any, interference. This helps to ensure liquid
level
sensing accuracy. As will be appreciated by those of skill in the art,
disruptions in the
interior surface of the mounting pipe may act as reflecting surfaces causing
interference and possibly false liquid level readings.
[00037] The air relief channels 24 and air relief slots 26 inhibit air
binding
which may adversely interfere with the rise and fall of liquid in the
absorption field
especially in pressure dose situations where water and/or effluent is pumped
into the
absorption field very quickly.
[00038] Figures 3 to 6 show the LLM device 10 installed in various
absorption
fields for measuring the total depth of the liquid level in the absorption
fields and for
detecting high liquid level conditions. For example, in Figure 3, the LLM
device 10
is inserted into the existing inspection port 100 of a gravel trench
installation with the
end of the mounting pipe 22 resting at the bottom of the gravel trench
installation.
The gravel trench installation comprises an underground layer of crushed stone
or
gravel 102 receiving a perforated pipe 104 extending from a distribution box
(not
shown). A layer of cover or backfill material extending to finished grade 106
is
disposed on the underground layer of crushed stone or gavel 102. In Figure 4,
a new
or retrofit inspection port 110 is formed just outside the edge of an existing
gravel
trench installation and the LLM device 10 is inserted therein.
[00039] Figure 5 shows the LLM device 10 inserted into an existing
inspection
port 120 of a leaching chamber installation comprising an underground leaching
chamber 122 and a layer of cover or backfill material extending to finished
grade 124
disposed on the leaching chamber 122. In this embodiment, both the inspection
port
120 and the mounting pipe 22 rest at the bottom of the leaching chamber 122.
In the
embodiment of Figure 6, the inspection port 130 is shorter so that only the
mounting
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pipe 22 rests at the bottom of the leaching chamber 122. The inspection ports
120 and
130 in the leaching chamber installations of Figures 5 and 6 may be existing
inspection ports or newly formed or installed inspection ports.
[00040] Figure 7 and 8 show the LLM device 10 installed in various
groundwater well monitoring applications for measuring the distance of the
liquid
level to the LLM device 10 or ground surface. For example, in Figure 7, the
LLM
device 10 is shown installed in a groundwater well 200. As can be seen,
groundwater
well 200 comprises a bore 202 through the ground 204 to a depth below the
typical
groundwater level. A pipe 210 having a cap 212 at its bottom end is inserted
into the
bore 202 such that the cap 212 rests at the bottom of the bore 202. The pipe
210 in
this embodiment is slotted adjacent its lower region, although those of skill
in the art
will appreciate that a lower screened region can be employed. The slots 214
allow
groundwater to enter the pipe 210. The lower region of the pipe 210 is
typically
formed of pipe sections that are threaded or otherwise joined together. The
pipe
sections are designed such that the interior of the pipe appears virtually
seamless to
avoid discontinuities in the inner surface that may cause ultrasound energy
wave
reflections. The pipe 210 extends above the ground surface 208 with the open
top end
of the pipe accommodating the LLM 10. An optional plug 220 formed of bentonite
clay or other suitable material seals a section of the bore 202 at a desired
location.
Packing 222 such as for example, sand or gavel fills the armular region of the
bore
202 surrounding the pipe 210 below the plug 220. Backfill 224 such as for
example,
sand or other suitable material fills the annular region of the bore 202
surrounding the
pipe 210 above the plug 220.
[00041] An optional protective steel casing 226 is accommodated by the
top
region of the bore 202 and extends above the pipe 210 and LLM device 10. A cap
228 is provided on the top of the steel casing 226.
[00042] In Figure 8, the top end of the pipe 212 terminates within the
bore 202.
As a result, the LLM device 10, which is accommodated by the top end of the
pipe
210, is positioned below ground level 208. In this case, an optional flush
mount
protective casing 230 is accommodated by the top region of the bore 202. A cap
232
is provided on the top of the casing 230 and is generally flush with the
ground surface
208. The backfill 224 provided in the annular region surrounding the pipe 210
above
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the plug 220 fills the annular region to a level below the top of the pipe 210
to
facilitate access to the LLM device 10.
[00043] Although the communications interface in this embodiment is a
RS-
485 wired communications interface, those of skill in the art will appreciate
that other
communications interfaces can be used. For example, communications interface
52
may be a wireless Zigbee interface that communicates calculated round trip
times
generated by the microcontroller 40 to one or more other LLM devices 10 before
the
calculated round trip times reach the remote control unit. The adjustment of
the
calculated round trip time to take into account the zero liquid level reading
made
during calibration can of course be carried out by the remote control unit.
The
adjustment value may be hard-coded or configurable. If desired, the LLM device
10
may comprise a humidity sensor instead of a temperature sensor. In this case,
the
output of the humidity sensor is sent to the remote control unit by the
microcontroller
40 to adjust the calculated round trip time to take air density into account.
Alternatively, the LLM device 10 may include both a temperature sensor and a
humidity sensor. In this case, the output of both sensors is sent to the
remote control
unit by the microcontroller 40 to adjust the calculated round trip time.
[00044] If desired, a mechanical backup sensor, such as for example a
mechanical float or magnetic reed switch, may be included in the liquid level
measurement device.
[00045] Rather than using a cap that threadably engages the outer
sleeve 18, a
slip cap or cover may be used to cover the top of the LLM device 10. Of
course, the
circuit board 14 need not be suspended within the inner sleeve 16 by a cap 17.
The
circuit board 14 may be mounted within the inner sleeve 16 in any suitable
manner.
[00046] The remote control unit may communicate with a single LLM device
10 or may communicate with a series of LLM device 10. In the latter case, the
sensed
liquid levels for the LLM devices 10 may be displayed individually or
together.
1000471 The remote control unit may be mounted in the structure that
is
serviced by the absorption field on its own or near the alarm panel. The
remote
control unit may also be mounted inside or outdoors. If the remote control
unit is
mounted outdoors, a sealed weather proof case is used to accommodate and
protect
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the remote control unit. Alternatively, the remote control unit may bc a
portable
wireless receiver that is carried by an operator between absorption field
locations.
[0048] Rather than having the microcontroller 40 transmit the
calculated
round trip time to the remote control unit for comparison with the threshold,
if
desired, the microcontroller 40 can be programmed to compare the calculated
round
trip time with the threshold and to signal the alarm condition when a high
liquid level
condition is sensed. The microcontroller can also be programmed to log the
sensed
liquid levels. In this manner, the need for the remote control unit is
obviated.
[0049] Also, if desired, rather than using separate transmit
and receive
transducers 42 and 46, a single transceiver transducer may be used both to
transmit
and receive ultrasound energy.
[0050] Although embodiments have been described above with
reference to
the drawings, those of skill in the art will appreciate that variations and
modifications
may be made without departing from the scope thereof as defined by the
appended
claims.
