Note: Descriptions are shown in the official language in which they were submitted.
CA 02644410 2009-02-10
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TITLE
Level Sensor System for Propane Tanks or the Likes
FIELD
[0001] The present invention concerns fluid level measuring in a
closed container, such as a propane tank, using ultrasound.
BACKGROUND
[0002] Many methods and systems are known to measure the fluid
level in a container, including those using ultrasounds.
[0003] Since ultrasound measurements often require a tight coupling
between the transducer assembly and the container, a drawback of current
level sensor system from the prior art that are adapted for pressurized tanks
or
tanks including corrosive liquids or gas is that the ultrasound transducer
assembly is directly mounted to the container or inside the container in a
housing which buffers between the transducer and the liquid. Thereby, such a
system is not adapted to be used on a plurality of different tanks or
containers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] In the appended drawings:
[0005] Figure 1 is a schematic view of a level sensor system for
measuring the level of propane in a conventional propane tank according to a
first illustrative embodiment of the present invention;
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[0006] Figure 2 is a schematic view of the sensor assembly part of
the level sensor system from Figure 1, the sensor assembly being illustrated
positioned under a conventional propane tank so as to be operatively coupled
thereto;
[0007] Figure 3 is a level sensor assembly according to a second
illustrative embodiment of the present invention;
[0008] Figure 4 is a schematic view of the sensor assembly from
Figure 3, illustrated positioned under a conventional propane tank so as to be
operatively coupled thereto;
[0009] Figure 5A is a level sensor assembly according to a third
illustrative embodiment of the present invention; the sensor assembly being
illustrated mounted on the side of a conventional propane tank so as to be
operatively coupled thereto;
[0010] Figure 5B is a schematic partially sectional view of the sensor
assembly from Figure 5A;
[0011] Figure 6 is a schematic partially sectional view of a sensor
assembly according to a fourth illustrative embodiment of the present
invention;
the assembly being illustrated mounted on the side of a conventional propane
tank so as to be operatively coupled thereto;
[0012] Figure 7 is a schematic view of a sensor assembly according
to a sixth illustrative embodiment of the present invention; the assembly
being
illustrated in operation as it is moved along the side of a conventional
propane
tank, operatively coupled thereto;
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[0013] Figure 8 is a schematic sectional view of a sensor assembly
according to a seventh illustrative embodiment of the present invention; the
assembly being illustrated mounted in a conventional propane tank, where the
transducer is inside a housing protected from the liquid;
[0014] Figure 9 is a schematic sectional view of a sensor assembly
according to an eight illustrative embodiment of the present invention; the
assembly being illustrated mounted in a conventional propane tank;
[0015] Figures 10 and 11 are schematic sectional views of a sensor
assembly according to a ninth illustrated embodiment of the present invention,
illustrating the use of a reflector between the transducer and the bottom of
the
tank for maximum fill level detection for example; Figure 10 showing the path
between the reflector and the transducer being partially immersed, while
Figure 11 shows the path between the reflector and the transducer completely
immersed;
[0016] Figure 12 is a schematic sectional view of a sensor assembly
according to a tenth illustrative embodiment of the present invention,
illustrating
the use of a reflector perpendicular to the emptying axis of the tank; and
[0017] Figure 13 is a graph illustrating representative signals when
transducers of the systems from Figures 5A and 5B to 12 are immersed in a
liquid (Curve A) or in a gas (Curve B).
DETAILED DESCRIPTION
[0018] The present invention concerns a level sensor system and
more specifically a level sensor assembly to measure the level of corrosive
and
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or pressurized liquid in a tank or container such as in a propane tank or, in
a
natural gas tank, or to measure the level of coolant liquid or others. The
present
level sensor system includes a transducer assembly and processing electronics
to be secured to the container outside or inside thereof, for continued level
measurement and or a switch or multiple switches operation.
[0019] As will be described furtherin, the level sensor system
according to the present invention comprises a controller and a sensor
assembly defined by a transducer assembly and a mounting assembly
configured for a quick connection or non permanent attachment of the
transducer assembly to the tank or container. The fact that the sensor
assembly is configured so as to be removably mounted to the tank allows
replacing the tank, for example when it is empty, without having to replace or
reconfigure the sensor assembly. For example, if one wishes to use the sensor
system on certain hardware such as a barbecue tank and replace the container
from time to time, one can do so without having to change the sensor.
[0020] As will be explained hereinbelow in more detail, the sensor
assembly according to the present invention can be configured for example for
direct connection to the tank or for tight coupling therewith when the
container
is positioned adjacent thereto.
[0021] More specifically, in accordance with a first aspect of the
present invention, there is provided a level sensor system for measuring the
level of a first fluid in a tank, the first fluid defining a fluid interface
with a
second fluid, the system comprising
[0022] an ultrasound transducer assembly for emitting ultrasound
pulses in the tank along a detecting path, for receiving ultrasound echoes
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indicative of at least one of the first and second fluids and for receiving
echo
signals representative of the at least one of the first and second fluids;
[0023] a controller coupled to the ultrasound transducer assembly
for receiving the echo signals and for determining a position of the -fluid
interface therewith; the level of the first fluid being defined by the
position of the
fluid interface; and
[0024] a mounting assembly for receiving the ultrasound transducer
assembly and for operatively mounting the ultrasound transducer assembly to
the tank for ultrasound measurement.
[0025] According to a second aspect of the present invention, there
is provided a level sensor assembly for measuring the level of a first fluid
in a
tank, the first fluid defining a fluid interface with a second fluid, the
system
comprising:
[0026] an ultrasound transducer assembly for emitting ultrasound
pulses in the tank along at least one detecting path, for receiving ultrasound
echoes indicative of at least one of the first and second fluids and for
receiving
echo signals representative of the at least one of the first and second
fluids;
and
[0027] a mounting assembly for receiving the ultrasound transducer
assembly and for operatively mounting the ultrasound transducer assembly to
the tank for ultrasound measurement.
[0028] The first fluid is, for example, a liquid in the tank, while the
second fluid is a gas above the liquid.
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[0029] According to a more specific embodiment of the present
invention, the echo signal representative of the at least one of the first and
second fluids is representative of the interface between the first and second
fluids.
[0030] The time of flight of the ultrasound pulse and reflected
echoes is indicative of the fluid level.
[0031] Other objects, advantages and features of the present
invention will become more apparent upon reading the following non restrictive
description of illustrated embodiments thereof, given by way of example only
with reference to the accompanying drawings.
[0032] In the following description, similar features in the drawings
have been given similar reference numerals, and in order not to weigh down
the figures, some elements are not referred to in some figures if they were
already identified in a precedent figure.
[0033] A level sensor system 10 for measuring the level of propane
in a conventional BBQ propane tank 11 according to a first illustrative
embodiment of the present invention will now be described with reference to
Figures 1-2.
[0034] The level sensor system 10 comprises a sensor assembly 12
including an ultrasound transducer 14 and a mounting assembly 18 for
operatively mounting the transducer 14 to the tank 11 for level measurement, a
controller 16 coupled to the ultrasound transducer 14, and a display output
device, in the form of a LCD module 20, which is coupled to the controller 16.
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Each of these components of the system 10 will now be described in more
details.
[0035] The controller 16 is in the form of a printed circuit board
(PCB) which includes conventional excitation electronics to drive the
transducer
14 in pulse mode, an amplifier processor and a conventional connector 17 to
receive the liquid crystal display (LCD) module 20. Both the excitation
electronics and amplifier can be provided with control electronics that change
the amount of excitations (duration and amplitude).
[0036] The PCB 16 receives echo signals from the transducer 14
and uses known algorithms to determine the position of the interface between
the liquid in the tank 11 and the gas thereabove. The PCB 16 calculation
includes computing the delay between the transducer 14 excitation and the
reflected signal (echo) from the interface of the liquid and the gas above the
liquid. This delay is known in the art as the Time of Flight (TOF). When
frequent
measurements are performed and/or when the position of the liquid level can
be approximated before measurement, a windowing technique can further be
implemented to minimize false measurements.
[0037] The LCD module 20 and/or transducer 14 can be coupled to
the controller 16 using respective interface cable 21 and wire 21' or
wirelessly.
In that later case, the LCD module 20, transducer 14, and controller 16 are of
course configured for that purpose.
[0038] Since ultrasound transducers and corresponding driving
electronics configured to operate the transducer in pulse and echo mode are
believed to be well-known in the art, they will not be described herein in
more
detail.
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[0039] As will now be described, the mounting assembly 18 so
positions the transducer 14 relatively to the tank 11 that the level of liquid
in the
tank 11 is measured from its bottom.
[0040] The mounting assembly 18 includes a ring-shaped body 22
having a central aperture 23, which houses the transducer 14. The mounting
assembly 18 further includes biasing elements, in the form of springs 26 (two
shown) having their respective proximate end 25 secured to the body 22. The
mounting assembly 18 finally includes a rubber layer 24 secured to the
transducer 14 using for example an adhesive such as glue, the rubber layer 24
acting as a coupling material between the transducer 14 and the tank 11.
[0041] The springs 26 allow biasing the transducer 14 upwardly so
as to force a tight contact with the propane tank 11 through the rubber layer
24
when the tank 11 is positioned thereon (see Figure 3). Of course, the length
of
the springs 26 is chosen so as to be greater than the height of the base 28 of
the tank 11 so as to provide a close contact between the transducer 14 through
the layer 24 and the tank 11.
[0042] Other biasing elements than the springs 26 can alternatively
be used to provide a contact between the tank 11 and the transducer 14
sufficient to allow transmission of the ultrasound waves. For example the
weight of the tank 11 can be sufficient in some applications, depending for
example on the configuration of the tank 11 and/or of sensor assembly 12.
[0043] As will be appreciated by a person skilled in the art, providing
a mounting assembly with springs 26 having a length sufficiently long allows
using the same level sensor system 10 with propane tanks of different lengths.
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[0044] The system 10 is removably secured to the tank 11 as
follows. According to the first illustrative embodiment, the distal ends 30 of
the
springs 26 sit on the base 32 that receives the propane tank, while according
to
a further illustrative embodiment, the distal ends 30 of the springs 26 are
secured to attachments (not shown) provided on the base 32 using fasteners
(not shown).
[0045] The tank 11 is then positioned on the base 32, over the
assembly 18. As described hereinabove, the tight ultrasound coupling between
the transducer 14 and the tank 11 is ensured by the biasing elements 26 and
the rubber layer 24.
[0046] The PCB 16 includes a magnetized mounting assembly 34
for its mounting onto the tank 11. According to this specific embodiment, the
PCB 16 is further covered by a weather-proof material and is provided with a
connector 17 which allows selectively disconnecting the LCD 20 from the PCB
16. Other fastening means, such as an adhesive or a strap-like assembly, can
further be used to secure the mounting assembly 34 onto the tank 11.
[0047] According to the first illustrative embodiment, the LCD display
unit 20 is intended to be connected to the controller 16 for selective level
readings and therefore no coupling elements are provided to secure the unit 20
to the tank or else.
[0048] The display unit 20 can also be provided with fastening
elements, such as magnets, for removably securing the unit onto the tank 11.
[0049] According to further illustrative embodiments of the present
invention, the display unit 20 is part of the controller 16 which is coupled
to the
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transducer 14 so as to be removable or not therefrom. The controller 16 can
also be integral to the sensor assembly 12.
[0050] According to a further illustrative embodiment, the display unit
and/or controller 16 are permanently secured to the tank 11 or an element
or object positioned adjacent thereto.
[0051] As mentioned hereinabove, the level sensor system 10
operates in pulse mode and therefore it operates in the time domain as will
now
be explained. The transducer 14 emits an ultrasound pulse towards the top of
the tank 11. Ultrasound echoes are produced by the reflection of the pulse at
the interface between the liquid in the tank 11 and the gas above or from the
interface between two liquids. This ultrasound echo is received by the
transducer 14 a certain time after the emission of the pulse, time which is
indicative of the distance/height of the interface relatively to the bottom of
the
tank 11. Providing the type of liquid/the speed of sound and the time of
flight,
the height of the liquid above the transducer can be calculated as described
hereinabove.
[0052] The echo signal produced by the transducer 14, which is
indicative of the reflection of the ultrasound pulse on the liquid interface,
is used
by the controller 16 to determine the level of liquid in the tank 11 and/or
any
other quantity related to the level of liquid in the tank 11, such as the
volume, or
weight of fluid for example. According to a further illustrative embodiment of
the
present invention, this information is then transferred via cable, wire or
wirelessly to another control unit for further processing and or display.
[0053] The controller 16 can further be programmed to frequently
measure the level of liquid in the tank 11 so as to determine the rate of
reduction in liquid and/or the flow rate and/or the amount of time left before
the
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tank 11 becomes empty. This information can be displayed on the display
unit 20.
[0054] As an illustrated method of determining the flow, the
processing unit may increase the sampling rate; by storing the acquired levels
corresponding to several measurements, the controller 16 can calculate the
slope/rate of the change of liquid height vs time. This slope correlates to
the
consumption of the fluid. Based'on the slope and the current level, which the
system may translate to volume, the system calculates the rate of consumption
of liquid in the tank. It may also calculate the amount of time left for
consumption at the same average rate.
[0055] Providing the identity of a plurality of fluids in the tank 11 is
known to the controller, the sensor system 10 can be used to measure the
quantity of each the liquids in the tank 11, if they are not mixed, by
determining
the position of the interface between two adjacent liquids for example.
[0056] The ultrasound transducer assembly 14 is not limited to
include a single transducer configured to emit ultrasound pulses and to
receive
ultrasound echoes. Two side by side emitter and receiver can also be used.
Using such a pair of emitter/receiver allows reducing the minimum level that
can be measured by the system. Other ultrasound transducers configurations
can alternatively be used as will be described hereinbelow in more detail with
reference to further illustrative embodiments.
[0057] According to still another illustrated embodiment of the
present invention, the display unit can be replaced by a simpler visual alarm,
such as a LED (light emitting diode) or by a sound alarm triggered, for
example,
by a press button, indicating to the user that a critical level has been
reached.
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[0058] Also, the configuration and size of the mounting assembly
may differ to the one illustrated in Figures 1 and 2. For example, the
transducer
14 can be sandwiched between the rubber layer 24 and the body 22, which is
not limited to having a ring shape.
[0059] As a person skilled in the art would appreciate, the rubber
layer 24 together with the biasing elements 26 provide for a tight joint
between
the transducer 14 and the tank 11 when the tank 11 is removably positioned
onto the sensor assembly 12. This tight connection allows for precise
ultrasound measurements.
[0060] The rubber layer 24 can alternatively be made of another
resilient material capable of transferring the acoustic wave and/or maintain
good contact between the transducer assembly and the container.
[0061] Turning now to Figures 3 and 4, a sensor assembly 36
according to a second illustrative embodiment of the present invention is
illustrated.
[0062] The sensor assembly 36 comprises an ultrasound transducer
14 and a mounting assembly 38 for operatively mounting the transducer 14 to a
tank 11 for level measurement.
[0063] The mounting assembly 38 includes a magnetized housing
40 and a ring-shaped body 42 for securing the transducer 14 to the housing 40.
The mounting assembly 38 further includes a resilient and flexible layer 44 on
top of the transducer 14 and the body 42. The layer 44, which can be made, for
example, of rubber, acts as a coupling interface between the transducer 14 and
the tank 11 as it has been described hereinabove.
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[0064] When the assembly 36 is removably attached underneath the
tank 11, the magnetic force between the housing 40 and the metal tank 11
forces the assembly 38 onto the tank 11 while compressing the rubber layer 44,
thereby providing a tight coupling between the transducer 14 and the tank wall
through the layer 44.
[0065] Even though the sensor assembly 36 is illustrated in Figure 4
mounted to the bottom of the tank 11, the configuration and functionality of
its
mounting assembly allows its mounting to other portion of the tank 11, such as
from the side. As a person skilled in the art would appreciate, the algorithm
of
the controller 16 has to be adapted according to the position of the sensor
assembly. For example, the controller of a level sensor system according to
the
present invention having a sensor assembly 36 mounted on the side of the tank
11 (see for example in Figures 5A to 11) will have to be configured to operate
in a switch mode, where the position of the sensor define the point of
measurement and detects if the liquid or gas is at the level where the sensor
is
attached to the side of the tank. Example of level sensor assemblies
configured
to operate in switch mode according to further illustrative embodiments of the
present invention will be described furtherin in more detail.
[0066] In switch mode, the sensor assembly 36 is mounted to the
side tank 11, outside thereof or within the tank 11 as will be illustrated
furtherin,
for emitting an ultrasound pulse along a path generally parallel to the bottom
of
the tank 11 and for receiving ultrasound echoes incoming along the same path.
[0067] In operation in switch mode, the sensor assembly produces a
different signal depending on whether the ultrasound pulse travels in a first
fluid, such as the liquid in the tank 11 (see Figure 13, curve A for a
representative output), in a second fluid, such as the gas above the liquid
(see
Figure 13, curve B for a representative output). Since a known liquid will
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provide a reflection on the tank wall or on a target after a known delay
following
the initial excitation signal, providing the nature of the fluids in the tank
11, and
the corresponding ultrasound signature, the sensor assembly can act as a
digital level sensing switch for these fluids.
[0068] Even though the sensor assembly 36 has been illustrated as
having a single transducer serving the purpose of both emitting the ultrasound
pulses and receiving the reflected echoes, other configuration of transducer
assemblies can also be used, including, without limitations, a pair of
ultrasound
emitter and receiver.
[0069] An example of sensor assembly 46 attached to the tank 11
for operation in switch mode is illustrated in Figures 5A-5B.
[0070] The sensor assembly 46 comprises a transducer assembly,
including a single transducer 14 and a mounting assembly, including an
embossed plate 48. The embossed plate 48 defines a central housing to
receive the transducer 14 and a peripheral section 50 to secure the mounting
assembly 48 to the tank, using fasteners or an adhesive to permanently or
removable secure the sensor assembly 46 to the tank 11. According to a
further illustrative embodiment (not shown), the peripheral portion of the
plate
48 can be magnetized so as to allow its coupling to the metallic tank 11.
[0071] The sensor assembly 46 further includes a compressible liner
52 to provide a tight joint between the transducer 14 and the tank 11 as
described hereinabove.
[0072] The transducer 14 is so mounted in the mounting plate 48
and the mounting plate is so mounted to the tank 11 onto the outside wall
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adjacent the bottom thereof that the ultrasound pulse 54 is emitted generally
parallel the bottom of the tank 11 at the level where one wishes to detect.
[0073] A level sensor system according to a third illustrative
embodiment of the present invention (not shown), which is equipped with the
sensor assembly 46 and is configured to operate in switch mode, includes a
controller configured to recognize the ultrasound signature of the liquid 56
in
the tank 11 and may therefore detect a liquid when the level thereof reaches
below the level of the sensor assembly 46. Curve A of Figure 13 is a
representative output when there is liquid in front of the sensor assembly 46
and curve B of Figure 13 represents an output when there is gas in front of
the
sensor assembly 46. In the case of multiple liquids in the tank 11, the
position
of the reflection signal, time is indicative of the type of liquid/liquid
mixture in
front of the sensor assembly 46.
[0074] The configuration and size of the mounting plate 48 may of
course be different than the one illustrated in Figures 5A and 5B. It can for
example be adapted for the shape and size of the transducer assembly.
[0075] The transducer 14 is coupled to a controller and may include
a display unit as described hereinabove.
[0076] It is to be noted that the precision of the measurement of the
sensor assembly 46 depends on the size of the transducer 14.
[0077] As can be seen in Figure 6, illustrating a sensor assembly 58
according to a fourth illustrative embodiment of the present invention, a
plurality
of transducers 14 can be mounted on the outside surface of the tank at
different positions along its height, using a mounting assembly 59 in the form
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for example of an elongated plate having embossed portions 60, each defining
a transducer housing as described with reference to Figures 5A and 5B. Each
housing 60 includes a compressible liner 52.
[0078] The sensor assembly 58 allows sequentially detecting when
the liquid level reaches each of three different heights in the tank 11,
corresponding to the position of the transducers 14. Similarly to the
transducer 14 in Figures 5A-5B, the transducer 14 is positioned relatively to
emit a ultrasound pulse 54 generally parallel the bottom of the tank 11.
[0079] Similarly to the assembly 46 in Figures 5A-5B, the assembly
58 can be removably mounted to the tank 11 or permanently attached thereto.
[0080] The accuracy of the measurement of the sensor assembly 58
depends on the number of transducers 14 and on the distance between them
since no detection occurs between two adjacent transducers 14.
[0081] Figure 7 shows a level sensor assembly 62 according to a
fifth illustrative embodiment of the present invention. As it is the case for
the
sensor assembly according to the other illustrative embodiments according to
the present invention shown herein, the sensor assembly 62 is to be coupled to
a controller 16 having an output device coupled thereto, such as an LCD
display 20, defining a level sensor system according to the present invention.
[0082] Since the sensor assembly 62 is similar to the assembly 36,
and for concision purposes, only the differences between the two assemblies
62 and 36 will be described herein in further detail.
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[0083] The sensor assembly 62 is intended to be moved on the
surface of the tank 11 along its height (see arrow 64) while ensuring that the
side of the assembly 62 provided with the liner is pressed upon the surface of
the tank 11 for better transmission and reception of the ultrasound waves
through the tank 11.
[0084] To minimize friction between the assembly 62 and the tank
11 and therefore to ease its movement thereon, the liner is made of a friction
reducing material such as TeflonT"". According to an alternative embodiment, a
gel is used to reduce friction.
[0085] As mentioned hereinabove, the assembly 62 is part of a level
sensor system according to an illustrative embodiment of the present
invention.
[0086] In operation, the operator, which is represented by the hand
67 on Figure 7, moves the sensor assembly along the height of the tank 11
(see arrow 64) until a display unit (not shown) or any other output unit
connected to the controller (also not shown) interactively informs the user
that
the sensor assembly is then positioned at the same level than the interface
between the liquid in the tank 11 and the gas above it as described
hereinabove. The controller is of course configured to recognize such an
interface as also described hereinabove (see Figure 13). More specifically,
when a 'reflection' is detected (see curve A in Figure 13), the system
recognizes that the liquid level is above the assembly 62 and interactively
informs the user thereof. The time of flight is indicative of the liquid type.
[0087] As will now be described with reference to further illustrative
embodiments of the present invention, sensor level assemblies according to
the present invention are not limited to be positioned outside the tank 11 or
used with conventional propane tanks, such as those used for BBQ.
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[0088] Figure 8 illustrates a sensor assembly for a level sensor
system according to a sixth illustrative embodiment of the present invention.
[0089] Such an assembly can be used for example in a big tank 71
where the reflected signal on the tank wall can be weak.
[0090] The sensor assembly 70 comprises a transducer assembly,
including a single transducer 14 coupled to a controller as described
hereinabove for example with reference to Figure 1 (not shown), and a
mounting assembly 72 for operatively mounting the transducer 14 within the
tank 71 to operate in a switch mode. The sensor assembly 70 is illustrated
mounted to a conventional pressure tank 71 filled with a pressurized gas in
liquid form 73.
[0091] The mounting assembly is in the form of a hollow cylinder 74
sealed at the bottom and inserted in an aperture 76 in the tank 71 so as to be
positioned generally perpendicular to the bottom 79 of the tank 71, the hollow
cylinder 74 defining a dip-stick. The transducer 14 is mounted to the cylinder
74
therein so as to emit an ultrasound pulse 77 generally parallel the bottom 79
of
the tank 71.
[0092] The transducer 14 is positioned adjacent or at the bottom of
the cylinder 74 and the cylinder 74 extends to the bottom 79 of the tank 71 so
that the detection occurs as close as possible to the bottom 79 of the tank
71.
[0093] Of course, the present invention does not limit the position of
the transducer 14 in or outside the tank 71 relatively to the bottom 79
thereof.
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[0094] The cylinder 74 is a made of a material capable of
withstanding the pressure in the tank 71 and to resist to any corrosive fluid
that
can be present therein.
[0095] The cylinder 74 includes a threaded portion 80 for its
mounting to a shoulder portion 82 of the tank 71 around the aperture 76. A nut
assembly 84 is also used to further secure the dip-stick 74 to the tank 71.
Further means can be used to secure the dipstick 74 into the tank 71
removably or not.
[0096] A mounting assembly having other configuration than the one
illustrated in Figure 8, allowing to operatively mounting the transducer 14 in
the
tank 71, can altematively be used. The present invention is not limited to a
dip-
stick having a cylindrical shape.
[0097] The cylinder 74 allows protecting the transducer assembly 74
from the environment in the tank 71. Depending on the application, the
controller can be inserted in the dip-stick 74 (see for example in Figure 10)
or
the transducer 74 can be coupled thereto using conventional wiring 78.
[0098] Figure 9 illustrates a sensor assembly 86 according to a
seventh illustrative embodiment of the present invention. Since the assembly
86 is very similar to the assembly 70, and for concision purposes, only the
differences between the two assemblies 86 and 70 will be described herein in
more detail.
[0099] The assembly 86 includes a plurality of transducers 14 (three
shown) mounted to the dip-stick 74 therein. Similarly to the assembly 58 in
Figure 6, the sensor assembly 86 allows sequentially detecting when the liquid
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level reaches each of three different heights in the tank 71, corresponding to
the three longitudinal positions of the transducers 14 in the tank 71.
[00100] The number and positions of the transducers 14 along the
height of the cylinder 74 may of course vary to yield different detecting
positions.
[00101] Moreover, a person skilled in the art would appreciate that the
three transducers 14 does not have to be mounted to the cylinder 74 so that
their pulses are oriented in the same direction, as long as they are
substantially
parallel.
[00102] Figures 10 and 11 shows a level sensor assembly 88 for a
level sensor system according to an eight illustrative embodiment of the
present invention. Since the assembly 88 is similar to the assembly 72 in
Figure 8, and for concision purposes, only the differences between the two
assemblies 88 and 72 will now be described in more detail. As will become
apparent upon reading the following description, the assembly 88 acts as a
fill
stop detector to determine a maximum level to fill up the tank 71.
[00103] In addition to the transducer 14, the cylinder 74 further
includes the controller 16 part of the level sensor system.
[00104] Also, the sensor assembly 88 includes an ultrasound reflector
90 mounted to the cylinder 74 outside thereof so as to be in the line of path
of
the ultrasound pulse emitted by the transducer 14.
[00105] As can be seen from Figures 10 and 11, because of the
ultrasound high attenuation in the gas (see curve B in Figure 13), the
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transducer 14 does not receive any reflection corresponding to the target 90
(or
from the tank wall) until the liquid has reached the level of the transducer's
face. The assembly 88 therefore allows detecting when the liquid 73 reaches
the height of the transducer 14. A signal similar to the curve A in Figure 13
is
then obtained.
[00106] The reflector 90 is mounted to the cylinder 74 via a frame
element, such as a rod 91. The distance between the reflector 90 and
cylinder's
end may vary, but is sufficiently close to the transducer 14 to allow enough
intensity to reach the transducer 14.
[00107] In some application, the bottom wall 79 of the tank 71 acts as
the target. However, providing a target closer to the transducer 14 allows
better
prediction of the reflection, therefore reducing the occurrence of false
detections.
[00108] The configuration, shape, distance and material of the
reflector 90 may of course vary than those illustrated.
[00109] As can be seen in Figure 13 and as described hereinabove
with reference to Figures 5A to 12, the level sensor assembly 88 allows
operating in the time domain. More specifically, with reference to Figure 13,
an
echo is received after a time "T", which corresponds to the delay between the
ultrasound excitation pulse being reflected on the reflector 90.
[00110] Curve A of Figure 13 is a representative output of a liquid
covering the space between the transducer and the reference target. Curve B
of Figure 13 is a representative output signal resulting when there is no
liquid
covering the gap between the transducer and the reference target. Using a
CA 02644410 2008-11-06
22
reflector, which can be for example be the bottom of the tank or one of its
walls,
and knowing the identity of the liquid in the tank, allows determining whether
the transducer is immersed in the liquid or in a gas thereabove. The use of a
time window allows reducing false detections.
[00111] Turning now to Figure 12 a sensor assembly 96 according to
a tenth illustrative embodiment of the present invention will now be descnbed.
Since most of the structural aspects of the assembly 96 are similar to those
of
the assembly 72 in Figure 8, and for concision purposes, only the structural
and
functional differences between these two assemblies 96 and 72 will be
described herein in more detail.
[00112] Similarly to the assembly 72 in Figure 8, the sensor assembly
96 allows detecting the liquid level in a switch mode.
[00113] A first difference between the assemblies 96 and 72 is that
the dip-stick 74 houses the controller 16.
[00114] A further difference between the two assemblies 96 and 72 is
that the assembly 96 includes a reference target 98, which is used to improve
the reflected signal quality to compensate for constrains of the tank 71, such
as
distance of the wall or non reflective walls, etc.
[00115] It is to be noted that many modifications could be made to the
sensor level systems described hereinabove for example:
[00116] - when the sensor assembly includes more than one
transducer part of a sensor level system to be operated in switch mode, each
transducer can be coupled to an independent controller configured as
CA 02644410 2008-11-06
23
described hereinabove or all the transducers can be coupled to a single
controller which is then configured to check and discriminate between the
return signals received from all the transducers so as to determine the level
corresponding to a detected change in said signals;
[00117] - the liquid mixture in the tank can further be determined by
the controller providing the change in the speed of sound for different
mixtures
and the distance between the transducer and the tank wall facing the
transducer;
[00118] - the output device coupled to the controller can be in the
form of a communication device that informs the user of the level of a
relative
information, such as a low level is reached. The controller or electronics can
for
example be configured to emit a distinctive sound when the fluid level reaches
a predetermined level.
[00119] Even though level sensor systems and assemblies according
to the present invention have been described in applications for measuring
level in a propane tank or more generally in a pressurized tank, they can also
be used in a tank including corrosive liquids and/or gases.
[00120] It is to be understood that the invention is not limited in its
application to the details of construction and parts illustrated in the
accompanying drawings and described hereinabove. The invention is capable
of other embodiments and of being practiced in various ways. It is also to be
understood that the phraseology or terminology used herein is for the purpose
of description and not limitation. Hence, although the present invention has
been described hereinabove by way of illustrative embodiments thereof, it can
be modified, without departing from the spirit, scope and nature of the
subject
invention as defined in the appended claims.
