Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02583006 2008-05-07
A MOISTURE DETECTION SENSOR TAPE AND PROBES TO DETERMINE
SURFACE MOISTURE AND MATERIAL MOISTURE LEVELS
FIELD OF THE INVENTION
The present invention relates to method for the detection of moisture
penetration into and on or across the surface of materials and particularly
but not
exclusively to the detection of the penetration of moisture into residential
and
commercial structures such as in the walls or roof of a building.
BACKGROUND OF THE INVENTION
Water intrusion into buildings is a massive and growing problem.
Leaking buildings cost homeowners, commercial property owners and property
insurers hundreds of millions of dollars every year. Even the smallest leaks
that
channel water into building walls can cause expensive problems. Structural
damage
to plywood sheathing and stud walls due to wood rot has been commonplace for
decades. Black mold or toxic mold that grows in the wet walls is known to
cause
severe physical problems for occupants as well as severe fiscal problems for
builders and insurance companies.
Early detection and location of building envelope penetration will allow
the builder or owner to identify developing problems and carry out minor
repairs.
These homeowners, builders, and insurance companies can avoid high costs
resulting from extensive structural damage, health problems, insurance claims
arid
potential lawsuits.
There are several types of moisture detection sensors available for
detecting water leaks.
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In United States patent 6,175,310 (Gott) issued January 16, 2001
there is disclosed an arrangement which uses exposed conductors on a tape of a
hygroscopic material where the current across the conductors is detected to
detect
moisture enveloping the tape.
In United States patent 6,377,181 (Kroll) issued April 23, 2002 there is
disclosed an arrangement which uses probes which are each connected to a
conductor pair communicating with a central monitor which issues an alarm when
moisture above a threshold is detected.
In United States patent 6,144,209 (Raymond) issued November 7,
2000 there is provided an arrangement which describes a location method using
a
combination of specially designed insulated and detection conductors cabled
together in a form helix. This design while useful for detection and location
of water
on floor like surfaces can not be placed between the roof deck and waterproof
membrane because of the large overall dimensions and the susceptibility of the
cable design to crushing and shorting.
US Patent 4,502,044 (Farris) issued Feb 26th 1985 discloses a plurality
of sensor elements defined by side by side pairs of conductors which are
adapted to
be mounted in two walls of a building and which connect to a central control
unit.
The control unit uses a transistor which acts to detect when voltage across a
resistor
reaches a value sufficient to turn on the transistor to emit an alarm signal.
British Patent Application 2,235,535 (Stewart) published 1991
discloses a plurality of sensor elements defined by tapes 3 which are mounted
in
walls of a building and connect to a central control unit in the form of a
leak detection
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US Patent 5,081,422 (Shih) issued Jan 14th 1992 discloses in general
a plurality of moisture sensor elements each defined by a side by side pairs
of
conductors which have a resistance characteristic which varies in relation
to''a
moisture content. Shih also discloses the use of probes which are connected to
the
wires and are driven into the material on which the wires are attached.
The present Applicants also disclose arrangements in Published PCT
Application WO/05/10837 published February 3, 2005. These arrangements use
detection tapes and probes are suited for detecting water intrusion in
selected areas
of a building structure. Also in United States Patent 7,292, 155 filed
September 19,
2005 entitled "A MOISTURE DETECTION SENSOR TAPE WITH LEAK LOCATE",
which corresponds to Canadian Patent No: 2,520,202 filed September 19, 2005,
is
disclosed an improved tape using four conductors which allow a location
process to
be used to locate the position of the leak along the tape. The disclosures of
the
above application of the present Applicant may be reviewed for further details
not
disclosed herein.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of moisture
detection.
According to the invention there is provided a method of detecting
moisture in an absorbent material, the method comprising:
providing a tape formed by a substrate of dielectric, hydrophobic
material, a layer of a mounting adhesive on a rear surface of the substrate
and at
least three spaced apart, elongate, generally parallel conductors mounted on a
front
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surface of the substrate and extending therealong;
attaching rear surface of the tape by the adhesive on to a surface of
the material so as to mount the conductors on the surface of the material;
engaging into the surface of the material a pair of conductive probes
such that each of the conductive probes penetrates the surface of the material
and
engages into the absorbent material;
electrically connecting each of the probes to a respective one of the
conductors;
at least one of the conductors of the tape being covered with a
moisture impermeable covering material such that the at least one covered
conductors is prevented from engagement with surface moisture on the tape;
two of the conductors of the tape being exposed to engagement with
surface moisture on the tape;
applying a voltage across the two conductors which are electrically
connected to the probes and monitoring currents passing between the connected
conductors so as to detect changes in resistance between the connected
conductors
caused by moisture in the material changing the resistance between the probes;
and applying a voltage across the two exposed conductors and
monitoring currents passing between the two exposed conductors so as to detect
changes in resistance between the exposed conductors caused by surface
moisture
on the tape.
Separating surface moisture measurements from material moisture
levels is of critical importance in the analysis of building envelope and roof
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performance. The arrangement described hereinafter overcomes the limitations
of
the current art by providing a method to separate and measure surface moisture
and
material moisture levels over a common moisture sensor and measuring circuit.
In a preferred method, the probes are electrically connected to the
5 respective conductors by penetrating each of the respective conductors with
a
respective one of the pair of conductive probes as it penetrates the surface
of the
material and engages into the absorbent material. However other arrangements
for
providing an electrical connection can be used including a connecting wire
which is
clipped to or soldered to the conductor.
Preferably the exposed conductors of the tape are covered by a
protective layer of non-hygroscopic, water pervious, dielectric material
secured to
the top surface of the substrate and extending over the conductors. This
covering
layer is preferable to protect the conductors while allowing the contact of
the
moisture with the conductors. It also can act to collect the moisture and hold
it in
electrical connection across the conductors. It can also act to diffuse the
moisture
over the area.
In one example there are three active conductors where one of the
connected conductors is exposed to the surface moisture and one of the
connected
conductors is covered so that one of the conductors acts in both the expose
pair and
the connected probe pair. Preferably this arrangement is used where there are
only
three conductors.
In another arrangement there are four conductors such that two of the
conductors are covered and electrically connected with a respective one of the
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probes and two of the conductors are exposed to surface moisture.
Preferably each of the conductors is a flat metal strip at least 6.5 mm
wide.
Preferably the exposed conductors are spaced apart by a distance of
at least 13 mm.
Preferably each probe is a rigid elongate conductive element of
corrosion resistant material which is forced into the material longitudinally
of the
element.
In the prime use of the method of the present invention, the absorbent
material is a moisture permeable element of a building construction. However
the
arrangements described herein can be used in other materials and fields.
Preferably the absorbent material with the tape thereon and the probes
therein is covered by a sheet material defining a component of the building
construction.
Preferably the probes each have a head which is covered by a
moisture impermeable covering material such as a piece of insulating tape or a
bead
of an insulating material.
In many cases the method includes providing a plurality of pairs of
conductive probes, penetrating each pair into the absorbent material at
respective
spaced locations along the length of the tape and electrically connecting the
pairs of
probes to the connected conductors at the location.
In accordance with another aspect of the invention the conductors of
the tape are connected to a monitoring unit, which applies the voltages and
receives
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the current, by a coupling cable which includes only two conductors, wherein
the
monitoring unit is preferably arranged to reverse the polarity of the voltage
applied to
the two conductors and wherein there is provided at least one diode for
guiding the
applied voltage to either the exposed conductors for detecting surface
moisture or to
the connected conductors for detecting the moisture in the material depending
on
the polarity of the applied voltage.
The arrangement described herein thus overcomes the limitations of
the current art by providing a novel and economic method to individually
measure
surface moisture and material moisture levels over the same measuring circuit.
Separating surface moisture measurements from material moisture levels has
been
found to be of significant importance in the analysis of building envelope and
roof
performance.
The arrangement thus includes a first pair of measuring conductors
mounted on an insulating substrate in an arrangement that provides for the
detection
of surface moisture and a second pair of measuring conductors mounted on the
insulating substrate to measure moisture content in the subject material at
selected
probed locations. In one form of the arrangement, the second pair of
conductors
may be formed using a combination of a single conductor mounted adjacent to
the
first pair of conductors whereby the single conductor is used in conjunction
with one
of the first pair conductors to form a second probed measuring arrangement.
In a first method, an elongated, dual mode, moisture detection sensor
is constructed of four parallel copper conductors laminated to an insulating
substrate. A first pair of conductors is arranged such that moisture on the
surface'of
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the substrate can contact and form a conduction path between the conductors of
the
first pair. The conduction path is detected by a resistance measuring circuit
thereby
detecting the presence of moisture. The second pair of parallel conductors is
constructed with an insulating layer covering the conductors such that surface
moisture can not form a conductive path across the pair.
Adjacent moisture probe pairs are inserted through the insulated
conductor pairs and into the absorbent material at selected locations.
Electrical
contact to the conductor pair is made as the probes are inserted through the
insulated conductors and into the absorbent materiaf.
In a second method, an elongated, dual mode, moisture detection
sensor is constructed of three parallel copper conductors laminated to an
insulating
substrate. A first pair of conductors is arranged such that moisture on the
surface of
the substrate can contact and form a conduction path between the conductors of
the
first pair. The conduction path is detected by a resistance measuring circuit
thereby
detecting the presence of moisture. A second parallel conductor circuit is
constructed by applying an insulating layer to a third conductor which is then
used in
combination with a single conductor of first pair to form a surface insulated
pair.
Adjacent moisture probe pairs are inserted through the conductors and into the
absorbent material at selected locations. Electrical contact to the conductor
pair is
made as the probes are inserted through the insulated conductors and into the
absorbent material.
For both the first and second methods, the moisture probe heads can
be surface insulated by a covering of insulating tape or insulating compound.
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With the addition of a diode steering circuit, both the surface and
probe resistance measurements can be carried out separately over a single pair
of
test leads. The circuit provides individual measurement of the first pair and
the
second conductor pair or circuit by application of a first and second
polarity. In a first
polarity, the diodes allow measurement of the first conductor pair by allowing
the test
voltage to be applied to the conductors while blocking measurement of the
second
pair or circuit.
In a second polarity the diodes allow measurement of the second
conductor pair or circuit by allowing the test voltage to be applied to the
conductors
while blocking measurement of the first pair.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
Figure 1 is an end elevational view of a tape to be used in a method
according to the present invention with three conductors laminated to a base
dielectric substrate which is attached by adhesive to a material to be
monitored for
moisture.
Figure 2 is a schematic illustration of a monitoring unit and circuit for
monitoring the resistance of the conductors of the tape of Figure 1.
Figure 3 is an end elevational view of a second embodiment of tape to
be used in a method according to the present invention with four conductors
laminated to a base dielectric substrate which is attached by adhesive to a
material
to be monitored for moisture.
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Figure 4 is a top plan view of the tape of Figure 3.
Figure 5 is a schematic illustration of a monitoring unit and circuit for
monitoring the resistance of the conductors of the tape of Figure 1.
DETAILED DESCRIPTION
5 Referring to Figure 1, there is illustrated a moisture detection tape 10
constructed by applying a non-water soluble adhesive 4 to a 40 mm wide x 0.1
mm
thick polyvinyl chloride substrate 3. Three 0.1 mm thick x 6.6 mm wide soft
bare
copper strips 1, 2 and 5 are laid down on the adhesive coated substrate with a
13.6
mm edge-to-edge separation. A non-hygroscopic, non-woven, water pervious layer
10 6 is applied over the polyvinyl substrate 3 and the copper conductors 1, 2
and 5.
The non-water soluble adhesive layer 4 is applied to the underside of the
polyvinyl
substrate 3 and is selected such that will adhere to common building materials
such
as wood, steel, concrete, etc. indicated at 7. A 40 mm wide x 0.1 mm thick
peel off
release layer (not shown) is applied over the underside adhesive layer 4,
prior to its
removal to expose the adhesive for application of the tape to the component 7.
When the tape is installed on a moisture absorbent building element 7,
for example wood, moisture probes 9 and 10 in pairs at spaced positions along
the
tape are inserted through two of the detection tape conductors at critical
point-
locations. The probes are constructed of stainless or copper-clad steel. The
probes
are of a dual prong design and can be inserted with a standard construction-
stapling
tool.
The conductor I is covered by an insulating layer 11 which is
impervious to moisture so that the conductor 1 is protected from contact with
any
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surface moisture.
The heads of the probes 9 and 10 which are exposed above the
conductors are covered by a piece of insulating tape or a patch of insulating
material
as indicated at 12.
The probes form a moisture level measurement system. The electrical
resistance between the probes, which are inserted parallel to one another in
the two
flat conductors, varies in proportion to the moisture content in the wood
material at
the location of the probe. By carefully selecting the probe dimensions,
distance
apart and depth of insertion, the measured resistance can be used to calculate
the
percent moisture content in the wood. This provides a noninvasive method to
effectively and continuously monitor moisture levels. Unacceptably high
moisture
content levels, that would otherwise go undetected with a surface moisture
detection
method, are readily detected.
Typically up to ten pairs of moisture probes may be inserted on a
single section of detection tape. The parallel resistance of the probes can
then be
measured remotely by a pair of conductors 15 and 16 as shown in Figure 2 that
are
spliced to the end of the detection tape and terminated on a pair of input
terminals
13 of a sensor device 14 that measures the resistance of the probe
combination.
In Figures 1 and 2 there are only three conductors where the
conductors 2 and 5 form a first pair which are exposed to surface moisture
since
they are bare or are covered by the moisture permeable layer 6. The conductors
1
and 2 form a second pair where the insulating layer 11 over the conductor 1
prevents the second pair being responsive to surface moisture since no current
can
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pass to the conductor 1 due to its covering layer and hence no current can
pass
between the conductors 1 and 2 due to surface moisture. However both
conductors
1 and 2 are penetrated by the probes 9 and 10 and hence this second conductor
pair is responsive to the current flowing between the probes due to the
presence of
moisture in the material.
The moisture level in the material can thus be detected by applying a
voltage across the two conductors 1 and 2 which are electrically connected to
the
probes and monitoring currents passing between the connected conductors so as
to
detect changes in resistance between the connected conductors caused by
moisture
in the material changing the resistance between the probes.
The surface moisture level can thus be detected by applying a voltage
across the two exposed conductors and monitoring currents passing between the
two exposed conductors so as to detect changes in resistance between the
exposed
conductors caused by surface moisture on the tape.
In Figures 1 and 2 there are three active conductors where the
conductor 5 is exposed to the surface moisture and the conductor 1 is covered
by an
insulating layer so that the conductor 2 acts in both the exposed pair for
detecting
surface moisture and the probe pair for detecting moisture in the material.
As shown in Figure 2 the conductors of the tape are connected to the
monitoring unit 14, which applies the voltages and receives the current, by a
coupling cable which includes only two conductors 15 and 16. The monitoring
unit
14 is arranged to reverse the polarity of the voltage applied to the two
conductors 15
and 16 and there is provided a pair of diodes 20 and 21 for guiding the
applied
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voltage to either the exposed conductors 2 and 5 for detecting surface
moisture or to
the probe conductors 1 and 2 for detecting the moisture in the material
depending on
the polarity of the applied voltage. Thus a positive voltage applied to the
conductor
15 with a negative voltage applied to the conductor 16 acts to cause a voltage
to be
applied across the conductors 1 and 2 to monitor current across the probes.
Reversing the polarity acts to apply the voltage across the conductors 2 and 5
to
monitor surface moisture
In Figures 3 and 4 there are four conductors 31, 32, 33 and 34 such
that two of the conductors 31 and 32 are covered and electrically connected
with a
respective one of the probes 9 and 10 and two of the conductors 32 and 33 and
bare
and thus are exposed to surface moisture. Thus the two sets of conductors are
separate and there is no conductor which is used for both surface and material
moisture.
In Figure 5 the same concept of diode switching is used but in this
case there are four diodes 41, 42, 43 and 44 so that the voltage is switched
between
the conductors 30 and 32 depending on the polarity of the voltage on the line
15 and
the voltage is switched between the conductors 31 and 33 depending on the
polarity
of the voltage on the line 16.
For use on roofs, all insulating, water pervious materials and
adhesives are selected to withstand roof membrane application temperatures of
200
C or greater for periods of several minutes or longer.
Since various modifications can be made in my invention as herein
above described, and many apparently widely different embodiments of same made
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within the spirit and scope of the claims without department from such spirit
and
scope, it is intended that all matter contained in the accompanying
specification sha[I
be interpreted as illustrative only and not in a limiting sense.
