Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02520202 2005-09-19
A MOISTURE DETECTION SENSOR TAPE WffH LEAK LOCATE
FIELD aF THE INVENTIQN
The present invention relates to an apparatus and method for the
detection and location of water penetration into residential and commercial
roof
structures.
BACKGROUND OF THE INVENTION
Water intrusion into roof structures is a major cancem. Leaking roofs
cost homeowners, commercial property owners and property insurers hundreds of
millions of dollars every year. Even the smallest leaks can cause expensive
problems. Structural damage to metal or plywood roof decking and rafters due
to rot
and rust has been commonplace for decades. Black mold ar toxic mall that gnaws
in the wet roof and wall areas is known to cause severe physical problems far
occupants as well as severe fiscal problems for builders and insurance
companies.
Flat or law slope roofs are commonly used for commercial and
multifamily building construction. While offering simplicity and limiting the
building
height, they are also the most difficult to seal and drain. Leaks occurring in
flat or
law slope roofs often appear on the inside of the building far from the paint
of origin.
New "green roof systems include live plants placed in a garden-like
setting on top of a roof structure. The garden roof areas help to control
rainwater
run-off, provide additional insulation, help reduce carbon dioxide and are
aesthetically pleasing. While providing many benefits, a green roof system
further
complicates roof problems. A leak can difficult to locate and can lead to the
dig-up
and destruction of large sections of the planted area.
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There are several types of moisture detection sensors available for
detecting water leaks. There are moisture detection tapes as described by
Vokey et
al. in Published PCT Application W0108110837 published February 3, 2005. These
detection tapes are suited for detecting water intrusion in selected areas of
a
building structure but are not well suited to roof applications.
In United States patent 6,175,31 r3 (Gotti) issued .lanuary 16, 2001
there is disclosed and arrangement which uses exposed conductors and
hygrascopic material that is not suited to roof applications where metal
decking and
high humidity levels can cause electrical shorts and false alarms.
The tape as described by Vokey et. al, while being better suited to roof
applications with both a protective covering over the conductors and no-
hygrascopic
components, does not provide for pinpointing the location of the water on the
tape.
In United States patent x,144,209 (Raymond) issued November 7,
200 there is provided an arrangement which describes a location method using a
l5 combination of specially designed insulated and detection conductors cabled
together in a farm helix. This design while useful far 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.
The moisture sensors may be placed directly under the waterproof
membrane which is often torched-an resulting in high temperatures that the
sensor
must survive. None of the earlier designs address this issue.
Precise location of a resistive water fault along a pair of conductors is
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a problem if a connecting cable is used to join the sensing conductors to the
monitoring unit. 1f the connecting cable conductors are of a different
resistance per
unit length or if the connecting cable is of an unknown length, then the
measured
distance to the water fault can be in error.
SUMMARY OF THE INVENTION
It is an object of the present invention to address one or more of the
above issues and provide a reliable detection and location system.
According to one aspect of the present invention there is provided a
moisture detection and location sensor apparatus comprising:
a substrate tape of dielectric, hydrophobic material;
two elongate, parallel, substantially fiat sensing conductors secured to
a top surface of the substrate tape;
a protective layer of non-hygroscopic, water pervious material secured
to the tap surface of the substrate tape and extending over the two sensing
conductors;
at least one substantially flat loop back conductor carried on the
substrate tape;
a protective layer of non-hygroscopic, water impervious material
secured to the to surface of the substrate tape and extending over said at
(east one
loop back conductor; and
a mounting adhesive on a bottom surface of the substrate tape.
Preferably said at least one loop back conductor is carried on the top
surface of the substrate tape parallel to the sensing conductors..
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Preferably, for high temperature applications, such as under torch-on
roof membranes, the dielectric materials and adhesives are heat resistant and
do
not melt or deform during roof construction.
Preferably said at least one loop back conductor comprises two
conductors that are used to loop-back one of the sensing conductors to
facilitate a
distance-to~fault measurement.
Preferably, when installed in a building, the two loop back conductors
are jointed to one of the sensing conductors at the distal end and at the near
end all
four conductors are jointed to insulated copper leads.
Preferably insulated copper leads are of the same electrical resistance
per unit length.
Preferably the four insulated leads are brought out to a termination box
for access, monitoring, testing and locating,
Preferably there is provided as part of the apparatus a bridge circuit
having four measuring arms which are each connected to a respective one of the
leads such that the measurement of the distance to a water fault is
accomplished by
balancing the bridge and reading from the balanced bridge the distance to the
fault,
which includes the length of the connecting leads.
Preferably there is provided as part of the apparatus a Time
Domain Reflectometry (TDR) sensing apparatus for measuring a length of the
leads
such that a pulse of energy is transmitted down at feast one of the leads such
that
when that pulse reaches an impedance change along the leads at the connection
thereof to the sensing conductors, part or all of the pulse energy is
reflected back to
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the instrument and the TDR instrument measures the time it takes for the
signal to
travel down the leads and back from the the impedance Change and the TDR then
converts this time to distance and displays the information as a distance
reading.
Preferably the sensing conductors are designed with significantly
different characteristic impedance than that of the leads so as to ensure a
strong
reflection from the connection therebeiween.
According to a second aspect of the invention there is provided a
method of detecting and locating moisture in a building structure comprising:
providing two elongate, parallel, substantially flat sensing conductors
i0 carried on a substrate of a dielectric hydrophobic material;
attaching the substrate to the building at a location where moisture is
to be to be detected;
providing a protective layer of non-hygroscopic, water pervious
material secured to the surface of the substrate and extending over the
sensing
conductors; and
providing at least one substantially flat Ioop back conductor;
providing a protective layer of non-hygroscopic, water impervious
material extending over said at least one loop back conductor;
connecting said at least one substantially flat loop back conductor to
one of said sensing conductors at a remote end of the sensing conductors;
detecting at a sensing end of the sensing conductors a change in
conductivity between the sensing conductors indicative of a moisture
penetration at
a position along the sensing conductors;
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and, when a moisture penetration is detected, connecting said at least
one substantially flat loop back conductor and said sensing conductors at the
sensing end of the sensing conductors so a sensing device which uses the
resistance of the sensing conductors and the at least one loop back to
determine the
position along the sensing conductors of the moisture penetration.
The preferred sensor is an elongate tape suitable for placement within
a building structure, adjacent to the building envelope or under a roof
membrane.
For high temperature applications, such as under torch.~an roof membranes, the
dielectric materials and adhesives should be heat resistant and not melt or
deform
during roof construction.
As described, the two conductors that are covered by a pervious
material form the water-sensing element. The remaining two conductors that are
covered and insulated by a water-impervious material are used to loop-back one
of
the detection conductors to facilitate the distance-to-fault measurement.
During installation the two insulated conductors are jointed to one of
the conductors at the distal end. At the near end all four conductors are
jointed to
insulated copper conductors that are preferably of the same electrical
resistance per
unit length. The four insulated conductors, which are typically in a two pair
cable,
are brought out to a termination box for easy access, monitoring, testing and
locating.
The measurement of the distance to the water fault is accomplished by
connecting the four conductors to the measuring arms of a bridge circuit. The
bridge
is then balanced and the distance to the fault, which includes the length of
the
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connecting cable, is read.
To accurately determine the location of the water fault across the
detection conductors, it is important to know the exact length of the two pair
cable as
the conductor's. This can usually be accomplished by physically measuring the
length of cable during installation ar by measuring the resistance of the
cable
conductors by looping them back. However, there may be circumstances where
neither measurement is possible. Far these cases another length measurement
method must be employed.
The length of lead cable to the detection and location conductors can
be measured using Tirne Domain Reflectametry (TDR). TDR works on the same
principle as radar. A pulse of energy is transmitted down a cable. When that
pulse
reaches an impedance change along the cable, part or all of the pulse energy
is
reflected back to the instrument. The TDR instrument measures the time it
takes far
the signal to travel dawn the cable and back from the location of the
impedance
IS change. The TDR then converts this time to distance and displays the
information
as a distance reading.
To provide this useful distance measurement function it is necessary
to deliberately design the moisture detection conductors with significantly
different
characteristic impedance than that of the connecting cable pair. This will
ensure a
strong reflection and accurate distance measurement to the conductor
pairldetection
conductors splice point.
The characteristic impedance of a transmission line is given by:
Z= ((R+jOL)I(G+jOC))"~ (1)
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Where: Z is the characteristic impedance in ohms
Ois the frequency in radianslsec.
R is the resistance per unit length
L is the induckance per unit length
S G is the conductance per un~ length
C is the capacitance per unit length
A TDR pulse is of a very short duration and contains only high
frequency components. This allows reduction of equation 1 to a high frequency
approximation given by:
Z= (U~)~n
From equation 2 it can be seen that only the inductance andlor
capacitance per unit of the detection conductors need to be changed to modify
the
high frequency characteristic impedance.
The magnitude of the reflected pulse at an impedance discontinuity is
given by the reflection coefficient:
Ro = (Z~ - Zo)~ (Z~ + Zo) (~1
Where: Zo is the impedance of the cable pair in ohms
Z, is the impedance of the detection conductors
The high frequency impedance of a typical communication or data
cable pair is about 700 ohms. To ensure a strong reflection at the cable pair
and
detection conductor splice point, the impedance of the detection conductor
pair must
be measurably different than that of the cable pair. From equation (3) this is
accomplished by adjusting the UG ratio to achieve the desired results. The
high
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frequency impedance of the detection conductors should be about double that of
the
cable pair. This will result in a reflection coefficient of 113 or better.
Approximately
113 of the incident pulse will be reflected back from the cable pair and
detection
conductors splice point thus providing a clear signature for an accurate
measurement of the cable p2~ir length.
With the length of connecting cable accurately known, the four
conductors of the moisture sensor tape can be conveniently connected to a four
terminal resistance bridge instrument. The precise resistance and therefore
distance to a water fault across the detection tape can then be measured.
Subtracting the known length of the connecting cable pair gives the correct
distance
along the detection conductors to the water fault.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
1 S Figure 1 is a view of the four conductors laminated to the dielectric
substrate.
Figure 2 is an expanded cross-sectional end view of the moisture
sensor design.
Figure 3 is a view of the MDT connected to an electrical bridge for
water fault locating.
Figure 4 is an illustration of the use of a TDR to measure the length of
the connecting cable.
Figure 5 is an illustration of a TDR display.
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1~
Figure 6 is an illustration of the moisture detection conductors
connected to a sensor unit.
DETAILED DESCRIPTIaN
Referring to the accompanying drawings, and particularly Figures 1
and 2, there is illustrated a moisture detection tape. The tape is constructed
by
laminating two moisture detection copper strips 1 and 2 and two loop-back
copper
strips 3 and 4 to a polyester substrate 5 using non-water soluble adhesive 9.
An
insulating layer of polyester 10 is laminated over the loop-back conductors
using
non-water soluble adhesive 8. A non-hygroscopic, nan-woven, water pervious
layer
6 is applied over the insulated loop-back conductors 3 and 4, detection
conductors 1
and 2 and polyester substrate 5. A non-water soluble adhesive layer 16 that
will
adhere to common building materials such as wood, steel, concrete, etc. is
applied
to the underside of the polyester substrate 5. A 50.4 mm wide x 0.1 mm thick
peel
off release layer 17 is applied over the underside adhesive layer 16,
The tape is constructed, in one example, by applying a non-water
soluble adhesive 9 to a 50.4 mm wide x 0.038 mm thick polyester substrate a.
Four
Q.051 mm thick x 6.35 mm wide soft bare copper strips 1, 2, 3 and 4 are laid
down
on the adhesive coated substrate 5 with a 5 mm edge-to-edge separation. The
adhesive coating 8 is applied over the loop-back conductors 3 and 4. A 0.076
mm
thick x 23 mm wide polyester insulating film 10 is laid down over the loop-
back
conductors 3 and 4 and the adhesive layer 7 applied over the insulating film
5. The
non-hygroscopic, non-woven, water pervious layer 6 is applied over all. The
non-
water soluble adhesive layer 1 ~ is applied to the underside of the polyester
substrate
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5. The 50.4 mm wide x 0.1 mm thick peel off release layer 17 is applied over
the
underside adhesive layer 16.
Wig the spy dimensions in the above detailed design the mutual
capacitance between the detection conductors 1 and 2 is about 27 pFlm and the
mutual inductance is about 1.5 oHlm. From Equation 2, this results in a high
frequency impedance of approximately 240 ohms that is at least twice that of a
standard data or communication pair. From Equation 3, this results in
reflection co-
efficient of 113 or better thus ensuring an accurate connecting cable locate
using
time domain reilectometry,
During installation in a location to be monitored, the two loop-back
conductors 3 and 4 at the distal end 21 are connected directly to one
conductor 2 of
the moisture detection conductors 1 and 2 by soldering a jumper wire 22 to the
conductors 2, 3 and 4, or other suitable means. At the near end 18, the
moisture
detection conductors 1 and 2 are connected by means of a Cannectlng cable 19
to a
sensor device 32, as shown in Figure 8.
During operation, the sensor device is arranged to emit a signal when
moisture causes a resistive path between the moisture detection conductors 1
and
2, that is current above a threshold value bows between the conductors 1 and
2.
As a second step in the operation, as shown in Figure 3, the distance
to a wet resistive fault is calculated by connecting a suitable four-terminal
bridge 20
to the near end of the connecting leads 19. The bridge is then balanced and
the
total distance to the fault location is read. The length of connecting lead 19
is
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subtracted from the total measured length to determine the distance along the
detection ronduetors to the fault location.
As shaven in Figure 3, the leads to the four conductors are provided by
4-wire cable 19, part of which provides the two le2~ds in Figure 8. Thus
during
normal operation for sensing the presence of a moisture penetration, only the
two
leads from the sensing conductors 1 and 2 are used.
When a penetration is detected, the bridge as a separate measuring
instrument is brought up to the sensing end of the conductors and connected to
the
four available leads sa that the location of the fault can be calculated.
If the length of the connecting leads 19 is unknown then a TDR
instrument 23 is used, as Shawn in Figures 4 and 5, to determine the length
19A of
the connecting cable 19 by measuring the time-of-flight and therefore distance
from
the incident pulse 28 to the reflected pulse 28. Thus, if required the bridge
is
disconnected and the TDR instrument connected into place to the leads 19 to
the
sensing conductors to make the necessary measurement.
In an alternate construction (not shown), the loop back conductors 3
and 4 are laminated to the underside of the dielectric substrate 5. A second
dielectric substrate is then applied under the loop-back conductors 3 and et
with the
adhesive layer 18 and release layer 17 applied under the second dielectric
layer.
In s~nather alternate method for detecting the location of the fault after
a signal has been detected from the conductors 1 and 2, a tape having a single
loop
back conductor 3 can be used, in replacement for the tape having the two loop
back
conductors 3 and 4 of Figure 1. In this arrangement, the single loop back
conductor
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3 is $rranged to loop-back one of the detection conductors 1 or 2. In this
case a
calculation can be carried out but the length and resistance per unit length
of the
loop back conductor 3 must be known and the length of the loop back conductor
accounted for in the distance calculation. Thus the total distance that the
bridge will
read is the distance to the fault on the detection conductor, the distance
from the
fault to the end of the conductor and the distance back along the loap-back
conductor. Therefore the calculation must factor in that the total conductor
length
measured is twice that of the detection conductor alone and if the loop back
conductor resistance per unit length is different than that of the detection
conductor
1.0 then there will be an error in the result.
All insulating, water perrrious 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 modii Ications can be made in my invention as herein
above described, and many apparently widely different embodiments of same made
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 shall
be interpreted as illustrative only and not in a limiting sense.
