Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2000-03-27
2002-11-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C250S559400, C250S573000, C250S574000, C340S605000, C340S619000, C356S432000, C356S436000, C356S440000, C356S445000
Reexamination Certificate
active
06484564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of a liquid leakage sensor for reliably detecting leakage of water, an acid solution, an alkaline solution, or other liquid that is electrically conductive, or leakage of alcohol, thinner, benzene, or other organic liquid that has dielectric properties, without being affected by bubbles.
2. Description of Related Art
Liquids are typically supplied through pipes to equipment in manufacturing plants. This requires the use of numerous joints and couplings to connect sections of pipe, and leakage of liquid from these joints is common. Depending on the type of liquid being used, regular manual inspection is required to check for leakage. Typical liquid leakage detection methods include conductive and volumetric techniques. Japanese Examined Patent Application Publication (kokoku) 4-70572 teaches a liquid leakage sensor technology for reliably detecting liquid leakage by emitting light from a light source to a filter that turns transparent when it absorbs liquid, producing a change in light transmitted or reflected by the filter when there is liquid leakage. This change in transmitted or reflected light is used to reliably detect liquid leakage.
FIG. 1A
illustrates the principle of this conventional reflection type liquid leakage sensor
20
. A test paper and case holder
4
of which the bottom
4
a
is coated black is fastened by a screw or other fastener
6
to floor
1
, and a white test paper (or cloth or synthetic resin)
8
is placed flat over bottom
4
a
. The bottom
4
a
is also a reflector. A case
12
of which the bottom
12
a
is transparent or semi-transparent is inserted to holder
4
. A light source
14
, photodetector
16
, and comparator or other detection means
18
are together housed inside the case
12
and connected by way of cable
26
to the outside of the case
12
.
It should be noted that the case
12
also functions as a dustproof and water-resistant cover. However, to facilitate penetration of leaked liquid
2
to the reflection area
8
b
in the middle of paper
8
, and shorten the liquid leakage detection time, a gap
10
is disposed between paper
8
and the case bottom
12
a
. This gap
10
is preferably no more than several millimeters in order to avoid contamination by dust and other foreign particulate, and to stably detect light reflected from paper
8
without also detecting external light noise. Replacing the paper
8
and installation are also made easier by constructing the filter so that the reflector
4
a
and case
12
are removable. It is also not generally possible to identify the source of liquid leakage. As a result, the paper
8
is also preferably round so as to respond more quickly to liquid leakage from any direction.
A liquid leakage sensor
20
thus comprised emits light
22
from the light source
14
, which is typically an LED, infrared laser diode, or optical fiber, to continuously monitor white reflected light
24
from the paper
8
by means of photodetector
16
. However, when leakage
2
occurs at the floor
1
, leaked liquid
2
gradually penetrates from contact area
9
to the reflection area
8
b
of paper
8
, and the contact area
9
of paper
8
turns from white to transparent due to liquid absorption. Because the reflector
4
a
below the paper
8
is black, the color of the paper
8
changes from white to black in the contact area
9
. Light
22
from the light source
14
is thus absorbed by the reflector
4
a
, significantly reducing the amount of light
24
reflected to photodetector
16
. The detection means
18
thus detects this change in reflected light, and senses liquid leakage.
The following problems not initially expected to occur with a conventional optical liquid leakage sensor as described above remain to be solved.
(A) When the holder bottom
4
a
is level to the floor
1
and the case bottom
12
a
is also substantially level, a high pressure line or large-diameter pipe bursts and a large volume of liquid leaks at once, the entire circumference of the bottom of case
12
is submerged in liquid at substantially the same time. When the leaked liquid
2
then penetrates gradually from the outside edge of the paper
8
toward the inside, the air in the gap
10
between holder bottom
4
a
and case bottom
12
a
becomes trapped (although part of the air escapes outside the case
12
as a bubble) in the center of the gap
10
and surrounded by the liquid. As shown in
FIG. 1B
, this bubble becomes trapped in the center of the reflection area
8
b
, preventing the reflection area
8
b
from turning transparent no matter how much time elapses. As a result, it is not possible to detect that a large volume of liquid has leaked.
(B) Large numbers of flat holders having a level bottom
4
a
are currently in use. Replacing each of the holders
4
fastened to floor
1
would require a massive amount of time, and is substantially impossible.
(C) In addition, paper
8
is a consumable and is thrown away each time liquid is detected. It is therefore preferable to be able to reuse the paper
8
<< or eliminate use of the paper
8
>>.
It should also be noted that the advantages of the liquid leakage sensor using paper
8
as described above include a simple design, reliable operation, stability and resistance to tipping over because it is fastened to the floor by a screw or other fastener, and the ability to detect high viscosity liquids in a relatively short period of time. On the other hand, users that would like to simplify or eliminate the work involved with installing the holder on the floor and replacing the test paper would like a liquid leakage sensor that does not use such paper and does not require floor installation.
Various liquid leakage sensors that do not use such a test paper have been proposed. These typically emit light to the bottom of the case, and evaluate the presence of liquid leakage by means of the amount of reflected light. However, if the case bottom is tight to the floor, it is very difficult for high viscosity liquids to penetrate to the middle of the case bottom. This means that the gap between the floor and the case bottom must be at the smallest at least 2 to 4 mm, which is significantly greater than in a sensor using paper as described above, and liquid leakage detection is not possible unless a large amount of liquid leaks so that the case bottom contacts the liquid.
Furthermore, if the case bottom is directly exposed to the floor surface, detection will be easily affected by the color of the floor surface, and when leaked liquid penetrates the sensor area, a large amount of unnecessary reflected light from the floor surface will also be detected, creating operating errors. Detection of liquid leakage based only on the amount of reflected light thus becomes unstable.
In addition, if the case is simply placed on the floor without fastening it to the floor, there is the danger of the case rising off the floor and even falling over.
SUMMARY OF THE INVENTION
The present invention was therefore conceived with consideration for the above-noted problems. An object of the invention is therefore to provide a liquid leakage sensor, paper for detecting liquid leakage, and a holder for detecting liquid leakage whereby liquid leakage can be stably and reliably detected without leakage detection being affected by bubbles even when a large volume of liquid leaks at one time.
A further object of the present invention is to provide a liquid leakage sensor, paper for detecting liquid leakage, and a holder for detecting liquid leakage whereby leakage of volatile liquids presenting the danger of flammable explosion can be remotely, safely, and reliably detected while taking care to prevent explosion and without leakage detection being affected by bubbles even when a large volume of liquid leaks at one time.
A yet further object of the present invention is to provide a liquid leakage sensor having a tilt detection function that does not use paper and can reliably, quickly detect liquid leakag
Ladas & Parry
Tsuden Kabushiki Kaisha
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