Note: Descriptions are shown in the official language in which they were submitted.
POROUS MEDIUM SENSOR
Field of the Invention
The invention relates to porous medium sensors for measuring parameters or
properties in porous media and, more particularly, it relates to a porous
medium
sensor having a sensing portion insertable in the porous medium with a
reference
port in gas communication with ambient air.
Description of the Prior Art
Porous medium sensors for monitoring parameters in soil are known. For
example,
tensiometers monitor matrix water potential Yin, (or soil moisture tension),
which is an
indirect measure of soil water content. Tensiometers are used in irrigation
scheduling
to help farmers and other irrigation managers to determine when to water.
Tensiometers can also be used in the scientific study of soil and plant
behaviors.
Typically the porous medium sensors are partially inserted in growing media,
such
as soil, for monitoring purposes. They include a sensing portion which is
insertable in
the growing medium and a head which extends outwardly. A section of the
housing
can also extend outwardly of the growing medium.
Several porous medium sensors, such as tensiometers, have a reference port in
gas
communication with ambient air. The reference port can be either immersed in
the
growing medium or located outwardly of the growing medium when a sensing
portion
of the porous medium sensor is inserted therein. VVater and porous medium
infiltration into the reference port, can bias measurements taken in the
growing
medium, even if the latter is located above the growing medium. To prevent
this
problem, it is known to cover the reference port with a water-repellent
membrane
[See for instance US patent application no. 2010/0263436 filed on April 30,
20101
However, the water-repellent membrane can seal in heavy growing media, for
instance the ones having high clay content. Furthernnore, if the water-
repellent
membrane is inserted in a fine growing media, a trapped volume of air can
surround
the water-repellent membrane and also bias the soil property measurements.
Furthermore, water-repellent membranes do flot perfectly repel water in all
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conditions, particularly if the sou l becomes hydrophobic. In particular
conditions,
water and/or small particles can thus infiltrate the sensor through the
reference port.
BRIEF SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to address the above mentioned
issues.
According to an aspect, there is provided a porous medium sensor comprising: a
sensing portion at least partially insertable in a porous medium and having a
housing
with a gas exchange aperture defined therein and a parameter sensor mounted in
the housing for measuring a parameter of the porous medium in which the
sensing
portion is insertable; a gas exchange tubing in gas communication with the gas
exchange aperture of the sensor portion and having a water-repellent membrane
inserted therein, the water-repellent membrane preventing water infiltration
in the
housing through the gas exchange aperture; a gas permeable protection sleeve
covering at least a section of the gas exchange tubing; and a water
impermeable
distal end collar covering a distal end of the gas permeable protective sleeve
and the
water-repellent membrane.
According to another aspect, there is provided a porous medium sensor
comprising:
a sensing portion at least partially insertable in a porous medium and having
a
housing with a gas exchange aperture defined therein and a parameter sensor
mounted in the housing for measuring a parameter of the porous medium in which
the sensing portion is insertable; a gas exchange tubing having a gas and
water
impermeable wall defining a gas exchange channel in gas communication with the
gas exchange aperture of the sensing portion and a water-repellent membrane
inserted in the gas exchange channel, the water-repellent membrane preventing
water infiltration in the gas exchange channel through a distal open end of
the gas
exchange tubing; a gas permeable sleeve covering at least partially the gas
exchange tubing and allowing gas communication with the water-repellent
membrane; and a water impermeable distal end collar covering at least a
section of
the gas permeable sleeve and a section of the gas exchange tubing including
the
water-repellent membrane to prevent water infiltration therein.
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In this specification, the term "porous medium" is intended to mean the soit
of a field
in agriculture, or the soit of pots for growing plants in a greenhouse or in a
nursery,
and any porous medium which fils with liquid. It can also be called a
substrate, a
mixture, a medium, or a soilless medium.
In this specification, the term "water-repellent" is defined as having a
degree of
resistance to permeability by and to damage caused by water in liquid form and
therefore encompasses the common terms of "waterproof" and "hydrophobic".
BRIEF DESCRIPTION OF THE DRAVVINGS
Fig. 1 is a perspective view of the porous medium sensor in accordance with an
implementation;
Fig. 2 is a perspective view, enlarged and fragmented, of a distal section of
the
porous medium sensor shown in Fig. 1;
Fig. 3 is a cross-section view of the distal section of the porous medium
sensor
shown in Fig. 2;
Fig. 4 is a perspective view, enlarged and fragmented, of a proximal section
of the
porous medium sensor shown in Fig. 1; and
Fig. 5 is a cross-section view of the distal section of the porous medium
sensor
shown in Fig. 4.
It will be noted that throughout the appended drawings, like features are
identified by
like reference numerals.
DETAILED DESCRIPTION
Referring to the drawings and, more particularly, to Fig. 1, there is shown a
porous
medium sensor 120 and, more particularly, a tensiometer apparatus (or water
potential sensor) in accordance with an embodiment. The tensiometer is
designed to
monitor matrix water potential in a porous medium such as, for instance,
earthen soit
or greenhouse sou.
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,
The porous medium sensor 120 has a sensing portion 121 with a housing 124 and
a
porous material tip 122. The porous material tip 122 extends outwardly from
the
housing 124 and is in direct contact with the porous medium when inserted
therein.
The housing 124 encloses a parameter sensor for measuring a parameter of the
porous medium in which the sensing portion 121 is inserted. The sensing
portion 121
is designed to be at least partially inserted in the porous medium. ln some
implementations, the sensing portion 121, such as the one shown in Fig. 1, is
designed to be wholly inserted in the porous medium. The design, the shape,
and
the components of the porous medium sensor 120 can vary from the above-
described and illustrated embodiment.
The housing 124 has a gas exchange aperture (not shown) extending throughout
an
upper wall 128 thereof. ln some implementations, the gas exchange aperture can
extend throughout any wall of the housing 124, such as and without being
limitative,
the lateral wall 130 of the housing 124. VVhen the sensing portion 121 is
partially or
totally inserted in the porous medium, the gas exchange aperture can also be
located in the porous medium. In the implementation shown in Fig. 1, the
sensing
portion 121 is totally insertable in the porous medium with the gas exchange
aperture located in the porous medium.
The gas exchange aperture is a reference port of the porous medium sensor 120.
The gas exchange aperture is conceived to allow gas exchange between air
located
outside the housing, i.e. ambient air, and an internai component (not shown)
of the
housing 124. For the tensiometer shown in Figs. 1 to 5, the gas exchange
aperture is
in gas communication with a pressure sensor (not shown) mounted in the housing
124. The pressure sensor compares the liquid pressure in a fluid chamber to
the
atmospheric pressure, which is provided through the gas exchange aperture,
which
is in gas communication with atmospheric gas.
Referring now to Figs. 3 and 5, there is shown that, to prevent liquid such as
water
and porous medium infiltration in the gas inlet aperture and pressure
variation due to
porous medium surrounding the gas exchange aperture, the gas exchange aperture
is connected to a gas exchange tubing 132. The gas exchange tubing 132 is a
tubular member with a peripheral wall 134 that defines a gas exchange channel
136.
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A proximal end 138 of the gas exchange tubing 132 is sealed to the housing 124
with the gas exchange channel 136 being aligned with the gas exchange aperture
and in gas communication therewith. The gas exchange tubing 132 is a flexible
and
elongated tubing made of a gas and liquid (water) impermeable material.
Therefore,
gas exchange with the gas exchange aperture occurs through the internai gas
exchange channel 136. In some implementations (without limitation), the gas
exchange tubing 132 is made of nylon, Tygon , water impermeable plastics,
rubber
or any other water impermeable tubing.
Referring now to Figs. 2 and 3, there is shown that the gas exchange tubing
132 has
a distal end 140, opposed to the proximal end 138 shown in Figs. 4 and 5. To
prevent water, growing medium particle or insect infiltration in the gas
exchange
channel 136, which could flow in the housing 124 through the gas exchange
aperture, a water-repellent membrane 142 is inserted in the gas exchange
channel
136, close to the distal end 140. In an embodiment, the water-repellent
membrane
142 is inserted in the gas exchange channel 136 in less than about 1 inch from
the
distal end 140 of the gas exchange tubing 132. Gas exchange between atmosphere
and the housing 124 occurs through the water-repellent membrane 142, the gas
exchange channel 136, and the gas exchange aperture.
The water-repellent membrane 142 is porous and gas permeable, i.e. it allows
gas
communication between atmosphere and the housing 124. The pressure on bath
sides of the water-repellent membrane 142 is substantially equal. The response
time
of the water-repellent membrane 142 to reach equilibrium is substantially
fast. In an
embodiment, the water-repellent membrane 142 can substantially resist to
microbiologic and chemical degradation. The membrane shape, thickness, and
size
can vary in accordance with the porous medium sensor design.
The water-repellent membrane 142 is shaped to fill the gas exchange channel
136
defined in the gas exchange tubing 132 and is tightly inserted therein. If an
adhesive
is used to secure the water-repellent membrane 142 to the gas exchange tubing
132, care should be taken to prevent or minimize membrane pore obstruction
with
the adhesive.
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For instance, without being limitative, Teflon , hydrophobic polypropylene and
polyethylene porous sheets, manufactured with free-sintered materials, such as
resins, glass, or metal beads can be used. These porous sheets provide filter
media
for ultrafine particles and flowability of gases. The filtration obtained
varies
depending on the micron size material selected.
The porous medium sensor 120 further includes one or a plurality of electric
wires
(not shown) having a proximal end operatively connected to internai
component(s) of
the housing 124 and extending outwardly therefrom. The electric wire(s) have
an
opposed distal end which can be connected to a head (not shown) of the porous
medium sensor 120 through an electric connector 160 operatively connected to
the
electric wire distal end. The head can include an electric circuit board (not
shown) of
the porous medium sensor 120. The electric wire(s) transferred data acquired
or
monitored by the sensor 120 to the electronic circuit board for further
processing.
The electric wire(s) can also provide power supply to the sensor 120 and an
.. electric/electronic circuit operatively connected to the sensor 120. The
head can
extend above the porous medium when the sensing portion 120 is at least
partially
inserted therein.
ln the embodiment shown, the electric wire(s) are surrounded by a common
sleeve
176 which extends between the housing 124 and the porous medium head. The
electric wire sleeve 176 has a proximal end 172 close to the housing 124 and a
distal
end 176 with the electric connector 160 mounted thereto for connection to the
head
(not shown). The electric wires and the electric wire sleeve 176, if any, can
extend
along the gas exchange tubing 132.
In the embodiment shown, the electric wire sleeve 176 and the gas exchange
tubing
132 are flexible components. In some implementations, the electric wire sleeve
176
and/or the gas exchange tubing 132 can be rigid components.
The porous medium sensor 120 further includes a protection sleeve 144
surrounding
at least a section of the gas exchange tubing 132. In the embodiment shown,
the
protection sleeve 144 also surrounds the electric wire channel 176 surrounding
the
.. electric wire(s). The protection sleeve 144 is a tubular member with a
peripheral wall
146 that defines an internai gas channel 148. At least a section of the gas
exchange
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tubing 132 extends in the internai gas channel 148. The protection sleeve 144
has a
proximal end 150, close to the housing 124 (shown in Figs. 4 and 5), and an
opposed distal end, close to the distal end 140 of the gas exchange tubing 132
(shown in Figs. 2 and 3).
.. The protection sleeve 144 is a flexible and elongated tubing made of gas
permeable
material. Furthermore, in some implementations, the protection sleeve 144 is
rodent
resistant (or anti-rodent). In an embodiment, the protection sleeve 144
includes a
metal wire mesh component such as a woven metallic component to offer a
protection against rodent damage.
.. In some implementations, the protection sleeve 144 covers the section of
the gas
exchange tubing 132 including the water-repellent membrane 142. In other
implementations, the protection sleeve 144 does flot cover the section of the
gas
exchange tubing 132 including the water-repellent membrane 142, the latter
being
covered solely by an end collar, as described in more details below.
In some implementations, the protection sleeve 144 is made of woven material
like
fiberglass, metals, plastics or natural fiber clothing or non woven
geotextile,
fiberglass or metals.
Referring back to Fig. 1, there is shown that the porous medium sensor 120
further
includes a proximal end collar 154 and a distal end collar 156. Referring now
to Figs.
4 and 5, there is shown that the proximal end collar 154 has a first end
sealed to the
gas exchange tubing 132 and the electric wire sleeve 176, and a second end
sealed
to the protection sleeve 144. In some implementations, the first end of the
proximal
end collar 154 can be sealed to the housing 124.
If the protection sleeve 144 surrounds directly the electric wire(s), the
first end of the
proximal end collar 154 can be sealed to the electric wire(s) and the gas
exchange
tubing 132.
Referring now to Figs. 2 and 3, there is shown that the distal end collar 156
has a
first end sealed to the protection sleeve 144 and a second end. The second end
can
be a closed end, if the protection sleeve 144 does flot surround the electric
wire(s) or
the electric wire sleeve 176. In an alternative embodiment, the second end can
be
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sealed to the electric wire(s) or the electric wire sleeve 176, if any. In the
embodiment shown, the second end of the distal end collar 156 is sealed to the
electric wire sleeve 176, which extends past the distal end collar 156.
In the embodiment shown in the figures, the electric wires are assembled
together
and surrounded by the electric wire sleeve 176. The protection sleeve 144
surrounds
the gas exchange tubing 132 and the electric wire sleeve 176. The proximal end
collar 154 surrounds the assembly including the gas exchange tubing 132, the
electric wire sleeve 176, and the protection sleeve 144. The first end of the
proximal
end collar 154 is sealed to the gas exchange tubing 132 and the electric wire
sleeve
.. 176 as there is a spacing between the protection sleeve 144 and the housing
124.
The second end of the proximal end collar 154 is sealed to the protection
sleeve
144. The distal end collar 156 surrounds the assembly including the gas
exchange
tubing 132, the electric wire sleeve 176, and the protection sleeve 144 with
its first
end sealed to the protection sleeve 144. The second end is sealed to the
electric
wire sleeve 176, which extends outwardly past the distal end collar 156. The
gas
exchange tubing 132 and the protection sleeve 144 have their distal ends 140,
152
located inside the distal end collar 156. The water-repellent membrane 142 is
also
covered by the distal end collar 156.
The distal end collar 156 covers a free end of the protective sleeve 144, a
free end of
.. the gas exchange tubing 132, and the water-repellent membrane 142.
The proximal end collar 154 and the distal end collar 156 are made of a water
impermeable material and, in an embodiment, a gas barrier material. For
instance,
the collars 154, 156 can be made of a thermo shrinkable polymer such as and
without being limitative any rigid or flexible water impermeable material like
rubber,
water impermeable plastics, nylon or metals.
Referring to Fig. 3, there is shown that the internai channel 148 of the
protection
sleeve 144 has a diameter larger than the combined outer diameter of the
electric
wire sleeve 176 and the gas exchange tubing 132. Thereby, a gas channel 162
extends longitudinally therein through which air and other gases can
circulate. The
gas channel 162 allows air to reach the water-repellent membrane 142 housed in
the
gas exchange tubing 132. In an alternative implementation (flot shown), the
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apparatus can be free of gas channel 162 since the protection sleeve 114 is
air
permeable.
The distal end of the apparatus further includes a gas chamber 158 defined
above
the water-repellent membrane 142. The gas chamber 158 allows gas exchange
between atmosphere and the gas exchange channel 136 through the protection
sleeve 144 and the water-repellent membrane 142. The gas chamber 158 is
defined
inside the distal end collar 156, i.e. the distal end collar 156 is not sealed
to the
water-repellent membrane 142. Thus, gas exchange between atmosphere and the
gas exchange channel 136 occurs through the protection sleeve 144, the gas
channel 162, if any, the gas chamber 158, and the water-repellent membrane
142.
In an embodiment (flot shown), the protection sleeve 144 can extend past the
water-
repellent membrane 142 and define the gas chamber 158 in the section of the
internai gas channel 148 extending past the water-repellent membrane 142. In
other
words, the section of the protection sleeve 144 which extends past the water-
repellent membrane prevents the distal end collar 156 from abutting the water-
repellent membrane 142 and thereby prevents gas exchange.
When the sensing portion 121 of the porous medium sensor 120 is at least
partially
inserted in the porous medium, a section of the assembly including the gas
exchange tubing 132, the electric wire sleeve 176, and the protection sleeve
144 is
located outwardly of the porous medium. This section further includes the
distal end
collar 156. Gas exchange between the housing 124 and atmosphere occurs through
the protection sleeve 144, which is gas permeable, the internai gas channel
148
extending in the protection sleeve 144, the gas exchange channel 136 including
the
water-repellent membrane 142, and the gas exchange aperture of the housing
124.
Liquid infiltration in the gas exchange aperture of the housing 124 is
prevented
through both the distal end collar 156 and the water-repellent membrane 142.
The
distal end collar 156 prevents important water quantity and particles to reach
the
water-repellent membrane 142.
ln the embodiment shown, the protection sleeve 144 extends along substantially
the
length of the gas exchange tubing 132. However, in some implementations, the
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protection sleeve 144 can extend along a shorter section thereof. In the
embodiment
shown, the distal end of the assembly, including the distal end collar 156
covering
the water-repellent membrane 142, prevents partial or complete obstruction of
the
gas exchange aperture or a portion of the housing 124 which could bias the
pressure
or other porous medium property measurements.
To measure a porous medium property, such as matrix water potential, in a
porous
medium, the sensing portion 121 is first inserted in the porous medium. The
assennbly including the gas exchange tubing 132, the electric wire sleeve 176,
the
protection sleeve 144, and the distal end collar 156 extends upwardly with
their distal
ends extending outwardly of the porous medium.
Once the sensing portion 121 is connected to a power supply (flot shown), if
needed,
the porous medium sensor 120 monitors the porous medium property in the porous
medium where the sensing portion 121 is inserted. Gas exchange with the
housing
124 inserted in the porous medium and atmospheric pressure therein is ensured
through the gas permeable protection sleeve 144, the gas exchange channel 136
having the water-repellent membrane 142 inserted therein, and the gas exchange
aperture. Therefore, for pressure measurement purposes, it is assumed that gas
pressure within the porous medium, at the sensing portion insertion depth, is
substantially similar to atmospheric pressure. The monitored data are
transferred to
an electronic circuit board which can display, transmit and/or record the
data.
Liquid and porous material infiltration is prevented by the combination of the
water-
repellent membrane 142 and the distal end collar 156, even if the gas exchange
aperture is located in the porous medium. More particularly, the distal end
collar 156
limits high pressure water and small particles to reach the water-repellent
membrane
142. Then, the water-repellent membrane 142 prevents accidentai liquid and
porous
medium infiltration which could have entered in the internai space defined by
the
distal end collar 156 and the protection sleeve 144 in the gas exchange
channel 136
and the gas exchange aperture, and thereby prevents partial or complete
obstruction
of the gas exchange aperture which could bias the porous medium property
measurements. While preventing accidentai liquid and porous medium
infiltration,
the water-repellent membrane 142 allows gas communication therethrough.
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In the embodiment shown and described above, the assembly including the gas
exchange tubing 132, the electric wire sleeve 176, and the protection sleeve
144 is
flexible. In some implementations, at least one of the gas exchange tubing
132, the
electric wire sleeve 176, and the protection sleeve 144 can be a rigid
component and
the resulting assembly can be rigid or substantially rigid.
In the implementation shown in Figs. 1 to 5, the porous medium sensor 120 is a
tensiometer and the gas exchange aperture is in fluid communication with a
reference port of the pressure sensor mounted in the housing 124. It is
appreciated
that even if the above described embodiment relates to tensiometers, the
assembly
including the gas exchange tubing, the water-repellent membrane, the
protective
sleeve, and the end collar can be mounted to various types of sensing portions
such
as and without being limitable pH, salinity, temperature, humidity, liquid,
gas, or gas
concentration sensing portions wherein gas communication between two sections
or
between a section and atmosphere is wanted while, simultaneously, preventing
.. liquid and porous medium infiltration. The sensing portion can also include
a sensor
detecting the irrigation status. The sensing portion can also include a LED
photo
detector for detecting fluid in sous or porous media.
The assembly including the gas exchange tubing, the water-repellent membrane,
the
protective sleeve, and the end collar can be used with modular or single piece
sensor apparatuses and with self-priming or filled fluid chamber sensor
apparatuses,
and any combination thereof. It is appreciated that the water-repellent
membrane
can be replaced by any liquid repellent membrane which is designed to prevent
liquid and porous medium infiltration in the gas exchange channel.
Moreover, although the embodiments of the porous medium sensor and
corresponding parts thereof consist of certain geometrical configurations as
explained and illustrated herein, not ail of these components and geometries
are
essential to the invention and thus should not be taken in their restrictive
sense. It is
to be understood, as also apparent to a person skilled in the art, that other
suitable
components and cooperation therein between, as well as other suitable
geometrical
.. configurations, may be used for the porous medium sensor according to the
present
invention, as will be briefly explained herein and as can be easily inferred
therefrom
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by a person skilled in the art. Moreover, it will be appreciated that
positional
descriptions such as "above", "below", "le", "right" and the like should,
unless
otherwise indicated, be taken in the context of the figures and should flot be
considered limiting.
Several alternative embodiments and examples have been described and
illustrated
herein. The embodiments of the invention described above are intended to be
exemplary only. A person of ordinary skill in the art would appreciate the
features of
the individual embodiments, and the possible combinations and variations of
the
components. A person of ordinary skill in the art would further appreciate
that any of
the embodiments could be provided in any combination with the other
embodiments
disclosed herein. It is understood that the invention may be embodied in other
specific forms without departing from the spirit or central characteristics
thereof. The
present examples and embodiments, therefore, are to be considered in ail
respects
as illustrative and flot restrictive, and the invention is not to be limited
to the details
given herein. Accordingly, while the specific embodiments have been
illustrated and
described, numerous modifications corne to mind without significantly
departing from
the spirit of the invention. The scope of the invention is therefore intended
ta be
limited solely by the scope of the appended claims.
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