Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02618092 2008-09-26
A METHOD TO DETECT AND LOCATE A BREACH IN VERTICAL OR
HORIZONTAL INTERSECTIONS IN A MEMBRANE OF A ROOF
The present invention relates to a system for testing roof membranes
to detect and locate damage and moisture penetration in the vertical and
corner
intersection surfaces of roof membranes. It has particular application to
testing the
integrity of vertical and sloped surfaces of residential and commercial
buildings.
This application is related to Canadian application Serial No 2,599,087
filed 17th August 2007 and entitled A METHOD AND APPARATUS TO DETECT
AND LOCATE ROOF LEAKS.
This application is related to Canadian application Serial No 2,618,999
filed 28th January 2008 and entitled A METHOD AND APPARATUS TO DETECT
AND LOCATE A BREACH IN A ROOF MEMBRANE.
This application is related to Canadian application Serial No 2,613,308
filed 3`d December 2007 and entitled METHOD AND APPARATUS TO DETECT
AND LOCATE DAMAGE AND BREACHES IN ROOF MEMBRANES.
BACKGROUND OF THE INVENTION
The failure to detect, find, and correct minor roof deterioration in the
earliest stages is considered the greatest cause of premature roof failure.
This is
particularly true of roofing materials applied on low-slope or flat roofs.
Costly roofing
problems are often the result of design deficiencies or faulty application of
the roof
system. Even when properly designed and applied, all roofing materials
deteriorate
from the contraction and expansion of roof decks and natural aging processes.
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Several methods have been used to try and locate roof leaks after they
have occurred. Electric capacitance meters identify leaks using a low-
frequency
method that measures dielectric constant changes in the roofing material as a
result
of moisture below the membrane. Infrared cameras allow technicians to scan
roof
surfaces for temperature differentials that signify moist areas through
changes in
thermal conductivity or evaporation. These methods are typically used in
forensic
analysis only after significant leakage has occurred.
Electric field mapping uses a wire loop around the perimeter of the roof
surface to introduce an electric potential between the structural deck and a
selected
roof area which is sprayed with water. The electric field potential caused by
a
conductive path to any roof membrane damage is then located using a voltmeter
and a pair of probes.
US Patent 4,565,965 issued Jan 21st 1986 to Geesen discloses an
electric field mapping arrangement for detecting leaks in flat roofs in which
electrical
pulses are transmitted through the moisture in the leak to the roof edge. The
roof is
then scanned by a pulse sensor and hand-held probe rods to find the leak by
locating the maximum amplitude. The disclosure of this prior patent is
incorporated
herein by reference.
The method as described by Geesen is applicable on horizontal low
slope or flat surfaces only and does not allow the testing of corner or wall
intersection areas.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and
method for the detection and location of moisture penetration at horizontal
and/or
vertical intersections and on the vertical or sloped surfaces of roof
inembranes.
s According to a first aspect of the invention there is provided a method
of locating a defect in the vertical or horizontal intersections of a roof
membrane, the
method comprising:
providing a ground connection to the roof deck
applying a voltage between the roof deck and a wet sponge like sensor
probe;
using a wet sponge like sensor probe and engaging the probe with the
roof membrane at vertical seams and joints on the membrane to detect a leakage
signal generated by current flowing between the roof deck and the sponge like
probe;
providing a receiver which acts to detect the leakage current between
the probe and wall or roof deck;
the receiver being arranged to provide to an operator controlling the
location of the probe a signal indicative of the leakage current so as to
allow the
operator to locate the defect by moving the probe to different locations;
wherein the probe is mounted on an insulated rigid base with a suitable
handle or pole such that the wet sponge like probe can be pressed against the
surface being tested while insulating the technician from the conducting
probe.
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The voltage applied is preferably a DC voltage but an AC signal could
also work. There are several ways to implement an AC detection circuit and one
could overcome any potential DC offsets from half-cell potentials. However DC
works well and is easier. The above patent of Geesen proposes an arrangement
by
which an AC signal can be used and a person skilled in the art can adapt such
an
arrangement to the present construction.
Typically, the test described and claimed herein is carried out on a
membrane before any overburden such as gravel or pavers are placed on top. In
this case all the seams. near the wall/roof deck interface and on the vertical
portions
of the parapet are tested using the technique. After this test the carriage
arrangement described herein is used to test the main area of the horizontal
roof
membrane.
The further technique of the framed probes described herein is used
when the deck is covered with an overburden or garden and the membrane is
covered.
Preferably the receiver includes a variable sensitivity and an analog
display for the differences in current detected.
Preferably the receiver provides an audible signal emitter such that a
signal indicating the maximum leakage current detected can be determined
audibly.
Preferably the audible signal emitter includes a voltage to frequency
converter.
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If required there may be provided an external connection to the
receiver common ground to form an external grounding or screening connection
to
allow electrical isolation of the area under test.
Thus un-insulated wire or metal foil can be placed on the membrane at
5 the end or ends of the area to be tested;
In this way, the un-insulated wire or metal foil connected to the
common ground by a connecting lead acts so as to block and ground any leakage
current outside of the area under test so that the probe will only detect any
leakage
current in the test area.
lo BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is an isometric view of a frame mounted leak location system
on a roof deck.
Figure 2 is a circuit schematic of the receiver of Figure 1 which
includes an auto-zeroing receiver system and an audible alert.
Figure 3 is an isometric view of a leak detection probe on a vertical
seam of a roof membrane,
Figure 4 is an isometric view of the leak detection probe on a
horizontal seam with isolating conductors applied.
Figure 5 is an isometric view of a roof membrane on a roof deck
including a basic illustration of a carriage arrangement for use in carrying
out a test
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on the main body of the membrane.
Figures 6A, 6B and 6C show respectively a top plan view, a bottom
plan view and a front view of the carriage and sensing system for use in the
general
method of Figure 5.
DESCRIPTION OF THE PREFFERED EMBODIEDMENT
The following description is taken from the above application and is
included to ensure description of the complete system with which the present
invention can be used.
The operation of the horizontal roof membrane leak location system is
shown in Figure 1. A bare conductor 3 is placed in a closed loop on top of the
roof
membrane area to be tested. A DC power source 4 is connected between the roof
deck and the energizing conductor 3 by a grounding cable 6 connected to a
building
ground point 7 on the roof deck and an energizing cable 5 connected to the
loop
conductor 3. The surface of the roof membrane is then sprayed with water so as
to
dampen the entire area 1 under test.
A probe mounting frame 8 with a receiver 9 attached to the frame is
positioned within the area to be tested. Two insulated conducting probes 11
carried
on the frame are connected to the input of the receiver 9, mounted on the
frame, by
two insulated connecting cables 10. A headphone and connecting cable 12 is
plugged into the audio output jack on the receiver 9. The frame is a fixed
structure
which provides two legs BA and 8B at fixed separation and position to hold the
probes at a fixed spacing. The legs are carried on a handle 8C which can be
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grasped by a single hand of the operator to simultaneously manipulate the
position
and orientation of the frame and the probes.
Thus the frame includes a pair of upstanding legs onto a lower end of
each of which a respective one of the probes is mounted so as to project
downwardly therefrom. The frame includes a center handle portion between the
legs.
An electrical circuit is formed between the roof deck via the building
ground 7 and the energizing cable 3 through any roof membrane defect 2 which
provides a conductive path through the membrane. With the roof circuit
energized,
the mounting frame 8 is positioned on the roof membrane and the probes 11
brought
into electrical connection with the roof membrane so that current flows to the
two
probes.
It will be appreciated that the amplitude of the current decreases along
any line extending from the defect to the peripheral cable 3.
The voltage connected between the roof deck and the peripheral
coriductor is constant so as to generate a constant current flow rather than
the use
of pulses which generate a varying current due to the charging current rush at
the
beginning of every pulse. The difference between the currents detected by the
two
probes is at a maximum when a line 11A joining the probes 11 is aligned with
the
defect. The current is at a maximum when the probes are closest to the defect.
With the probes fixed on the frame 8, the frame is rotated by the
operator until the maximum difference between the two currents is detected to
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provide a maximum pulse rate in the headphones 12 which corresponds to a
maximum reading on the signal level meter 9. In this position, the operator
knows
that the line 11A joining the probes is aligned with the defect. The mounting
frame is
thereby brought into directional alignment with the current 13 from the defect
so as
to indicate the direction to the location of the defect 2. The mounting frame
is then
advanced in steps along that line 11A until a maximum signal level and audible
pulse rate is achieved thus indicating the actual location of the defect.
The schematic diagram for the receiver unit is shown in Figure 3, The
two mounting frame probes 11 are connected by the insulated cables 10 to the
respective input terminals 23 and 24. One side 23 is connected to the negative
summing input of a first stage op-amp 28 through a resistor R1. The other side
24 is
tied to circuit common. Diodes Dl and D2 provide input protection. The gain of
the
first stage op-amp is set by resistor R2 and potentiometer P1 while capacitor
Cl
filters out any unwanted noise.
The output of the first stage op-amp 28 is tied to the input of a second
stage op-amp 29 through a resistor R6. Resistors R6 and R8 set the gain of the
second stage op-amp 29 to unity. The positive summing input of the second
stage
op-amp 29 is tied to common through a resistor R7.
A voltage-to-frequency converter 32 has an input which is connected to
the output of the second stage op-amp 29. The output of the V to F converter
32 is
applied to the input of an audio-amp 34 through a volume control 33. The audio
output of amp 34 is connected to the headphones 12 or to a speaker 24.
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The output of the second stage op-amp 29 is connected to voltage
limiting diodes D3 and D4 through a resistor R9. A signal level meter 31 is
connected in series with a scaling resistor R10 across the diodes D3 and D4.
In order to avoid the need for zero offset adjustment of the meter circuit
31 as the supply voltage V changes, there is provided a circuit component
which
provides self adjustment of the common ground G of the main circuit connected
to
the op-amps 28 and 29. Thus the positive summing input of a third op-amp 30 is
tied to the half the supply voltage point between +V and -V through equal
value
dividing resistors R4 and R5. The negative summing input and output port of op-
amp 30 forms the circuit common G. In this way there is automatic adjustment
of
the circuit ground so that the meter is always centered at zero voftage
difference
between the probes and the meter moves away from the center position when a
current difference is detected.
The above technique of the frame mounted probes is typically used
when the deck is covered with an overburden or garden and the membrane is
covered.
Turning now to the arrangement shown in Figures 3 and 4, the
operation of the vertical roof membrane leak location system is shown in
Figure 3.
The horizontal roof membrane 51 has a vertical membrane 52 at a roof parapet
52A.
The receiver 54, which is of the construction and arrangement previously
desoribed,
is operated to apply the positive side of the power supply to a building
ground point
56 through a connecting cable 55. A connecting cable 57 and headphones 58
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provide the audible output signal from the receiver 54.
In the example in Figure 3, a sensor 59 in the form of a wet sponge is
held against a seam on the vertical membrane. A connecting cable 60 ties the
conductive wet sensor 59 to the input of the receiver 54. Moisture in the
sensor 59
5 makes electrical contact with the membrane. Any breach in the vertical
portion of
the membrane will result in a conductive path forming through the breach to
the
parapet wall. A fault current will flow from the positively grounded building
56
through the breach to the wet sensor 59 and connecting cable 60 into the input
of
the receiver 54. The detection circuit of the receiver 54 as described above
will
10 generate an audible signal and meter deflection in response to the leakage
current.
The same probe can be wiped over a horizontal seam at an edge of
the roof.
The schematic diagram for the receiver unit 54 is shown in Figure 2.
The building ground is connected to the positive supply via the ground jack
26. The
is sensor 59 is connected via a cable 10 to the negative summing input of the
first
stage op-amp 28 through the input jack 23 and current limiting resistor R1.
Diodes
D1 and D2 provide input protection. The gain of the first stage op-amp is set
by
resistor R2 and potentiometer P1 while capacitor C1 filters out any unwanted
noise.
The output of the first stage op-amp 28 is tied to the input of the
second stage op-amp 29 through a resistor R6. Resistors R6 and R8 set the gain
of
the second stage op-amp OA2 to unity. The positive summing input of the second
stage op-amp 29 is tied to common through a resistor R7.
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The voltage-to-frequency converter 32 has an input which is connected
to the output of the second stage op-amp OA2, The output of the V to 1=
converter
32 is applied to the input of the audio-amp 34 through a volume control 33.
The
audio output of amp 32 is connected to the headphones 58 or to a speaker 35.
The output of the second stage op-amp 21 is connected to voltage
limiting diodes D3 and D4 through a resistor R9. A signal level meter 31 is
connected in series with a scaling resistor R10 across the diodes D3 and D4.
The sensor 59 comprises a sponge 65 mounted on a backing plate 66
carried on an insulating handle 67. Thus the contact from the cable 60 is
connected
to the conductive plate 66 for communication of current through the moisture
in the
sponge. However the operator moving the sensor is isolated from the current by
the
insulated handle 67.
The handle can comprises a simple transverse bar at the rear of the
probe or the handle can comprise an elongate pole extending from the rear of
the
probe allowing the operator to stand and wipe the probe over seams from a
standing
position.
The contact portion of the sensor 59 can comprise any flexible material
which can wipe over an area to be sensed and provide contact between the
material
and the membrane over the whole area of the material while carrying moisture
into
contact with the membrane. Thus the material can be a sponge or can be a
fabric
such as felt or can be other materials which have the required characteristics
of
carrying the liquid into contact with the membrane and sufficient flexibility
to deform
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slightly where required to remain in contact with the membrane over changes in
surface height and over changes of angle.
As the peripheral conductor 3 of Figure 1 as no effect in generating a
potential difference in the area of the parapet 52A, this arrangement uses
current
communicating directly between the roof deck and the sponge sensor and acts to
measure the absolute value of that current against a fixed comparison value
provide
at COM terminal 24 which is connected to the positive input of the amplifier
28.
Thus the sponge sensor acts to apply moisture to the membrane to
create the conductive circuit and acts as a sensor to detect the value of the
current
so caused. It will be appreciated that the current will vary as the sensor is
moved
closer to a breach from a zero current where there is no breach to a maximum
directly at the breach. The comparison with the fixed value thus locates this
maximum which is communicated to the operator either using the meter 31 or the
headphones 58.
In certain situations a conductive path will exist beyond the area under
test due to extensive wetting of the membrane. In Figure 4 a method to isolate
the
area under test is illustrated. A horizontal seam 73 next to the parapet wall
72A is
shown with a water path 71 extending beyond the test area. A metallic strip 72
is
placed across the water path 71 on one end of the area to be tested and a
second
metallic strip 73 placed across the other end of the area to be tested. The
metallic
strips are connected to the circuit common ground via cables 74 and 75. Any
fault
current flowing along the water path from membrane breaches outside of the
test
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area is isolated by the metallic strips thereby isolating the test area.
Typically, the test described above is carried out on a membrane
before any overburden such as gravel or pavers are placed on top. In this case
all
the seams. near the walVroof deck interface and on the vertical portions of
the
parapet are tested using the technique.
After this test, the carriage arrangement described below is used to
test the main area of the horizontal roof membrane.
The overall arrangement of the carriage arrangement can best be seen
with reference to Figure 5. A roof membrane 62 is illustrated which is applied
as a
direct covering layer over a concrete roof deck 61. The deck is typically of
concrete
but can be of any suitable material to provide the necessary structural
strength and
can be steel or wood. The membrane is an impervious material such as plastics
and
is sealed at any joints to provide a continuous water barrier over the roof
deck. This
barrier is intended to provide the leak prevention and any penetration therein
caused
by a puncture or faulty seal or by wear can allow the moisture to penetrate to
the
deck where it can cause damage or can continue into the structure to cause
damage
to internal structures.
A defect in the membrane 63 allows water 4 to intrude and forms a
conductive path to the roof deck. The conductive outer 67 brushes and inner 68
brush are placed on the top surface of the membrane 62 with the outer
perimeter
conductive brushes 67 surrounding the inner brush 68. The brush sets are
positioned so as to be in intimate contact with the wetted surface 64 of the
test area.
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The outer sweep detection circuit 65 and inner sweep detection circuit 66
which
share a common power supply are connected to the outer brush set 67 and inner
brush set 68 respectively with the common positive side of both connected to a
grounding point 69 on the deck.
A DC potential is applied between the roof deck 61 and the wetted
area 64. At the membrane damage site 64 there is a conductive path through the
membrane and a leakage current 70 travels through the damage point and back to
the outer conductive brush 67. The return current picked up by the outer
brushes is
measured and displayed on the outer sweep circuit 65. As the outer brush
perimeter
surrounds the inner brush sensor, very little of the return current reaches
the inner
brush 68. The sweep system is then moved forward over the membrane towards
the defect and when the outer brush passes over the damage site, the inner
brush
picks up the return current and provides a visual and audible alarm. The
damage
site is thereby located.
The detector circuit is substantially as shown and described above.
The mechanical arrangement of the apparatus is illustrated in Figures
6A, 6B and 6C. A horizontal platform or carriage 80 with a flat top wall and a
depending side wall 85 forming four sides of a rectangular carriage. The
carriage is
carried on four swivel wheels or casters 81 attached to the top plate by
mountings
86. The carriage supports an outer brush assemblies defined by two parallel
front
and rear brushes 82 and two parallel side brushes 87, thus defining a
rectangular
outer area just inside the outside wall of the carriage. Inside the outer
rectangular
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area is provided a single transverse brush defining an inner brush 83.
Vertically
floating brackets 84 position the outer brushes and allow vertical movement of
the
brushes as the platform travels over the membrane surface. Simiiar brackets 88
carry the inner brush. The brushes are formed as a strip from conductive
bristles
5 carried on a base so that the base can float upwardly and downwardly from
pressure
of the roof against the tips of the bristles so that a constant electrical
contact is
maintained with the roof.
A simple manually graspable handle assembly 90 is attached to
brackets 89 on the top plate of the carriage. The sweep circuits are mounted
in a
10 housing 91 and attached to the handle 90 assembly at a position below a top
hand
rail of the handle assembly.
