WO2015183465A1

WO2015183465A1 - Liquid leakage detector and method for detecting liquid leakage

Info

Publication number: WO2015183465A1
Application number: PCT/US2015/028712
Authority: WO
Inventors: Yukio Nojiri; Kengo TAKASU; Yoshiaki Sato
Original assignee: 3M Innovative Properties Company
Priority date: 2014-05-28
Filing date: 2015-05-01
Publication date: 2015-12-03
Also published as: TW201602545A; JP6395444B2; JP2015224983A

Abstract

A liquid leakage detector that can suppress false detection regardless of use over a long period of time and a method for detecting liquid leakage. With a liquid leakage detector 1, the presence or absence of a leakage of a fluid is determined using the liquid leakage determining unit 6 to compare an output value R1 of the electrical resistance, output from a liquid leakage sensor 7, according to the amount of liquid present in a surrounding area, and a first threshold value S1 that fluctuates according to the output value R1. Accordingly, when the output value R1 gradually fluctuates due to factors over time such as adhesion of filth onto the surrounding area of the liquid leakage sensor 7, the first threshold value S1 also gradually fluctuates in accordance with the fluctuation of the output value R1, and therefore, false detection that a liquid is leaking can be suppressed. According to the above, false detection can be suppressed regardless of use over a long period of time of the liquid leakage detector 1.

Description

LIQUID LEAKAGE DETECTOR AND METHOD FOR DETECTING LIQUID

LEAKAGE

FIELD OF THE INVENTION

[0001]

The present invention relates to a liquid leakage detector and a method for detecting liquid leakage.

RELATED ART

[0002]

Conventionally, methods for detecting liquid leakage on a floor of, for example, a factory, an apartment, restaurant, coffee shop, and the like are known to utilize a fluctuation in electrical resistance due to the liquid leakage. For example, in patent document 1 , a liquid leakage sensor (liquid leakage detecting device) is used in which electrical resistance fluctuates in the presence of a non-insulating liquid to determine the presence or absence of a liquid leak based on output data on the electrical resistance. Patent Documents

Patent Document 1

[0003]

Patent Document 1 : Japanese Examined Patent Application Publication No. H6-

29825

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

[0004]

Liquid leakage detecting devices such as that described above are typically disposed on a floor and the like, making cleaning difficult if filth adheres. Meanwhile, it is desirable that the liquid leakage detector, while disposed on the floor and the like, continues to detect liquid leakage with high precision for at least, for example, several years. However, when a liquid leakage detector is used for an extended period of time on a floor and the like, there is a risk of false detection of liquid leakage due, for example, to filth such as dust and the like depositing around the liquid leakage detector, and also due to fluctuation in output data on electrical resistance resulting from factors over time such as adherence of liquid onto the dust due to condensation and the like. Due to the above, there is a need for a liquid leakage detector that can suppress false detection regardless of use over a long period of time and a method for detecting liquid leakage.

MEANS FOR SOLVING THE PROBLEM

[0005]

The liquid leakage detector according to one aspect of the present invention includes: a liquid leakage sensor that outputs an output value according to an amount of a liquid present in a surrounding area; and a liquid leakage determining unit that sets a first threshold value and determines the presence or absence of a leakage of a liquid by comparing the output value output from the liquid leakage sensor to the first threshold value; wherein the first threshold value fluctuates according to the output value.

[0006]

With a liquid leakage detector thereof, the presence or absence of a leakage of a fluid is determined using the liquid leakage determining unit to compare the output value, output from the liquid leakage sensor, according to the amount of liquid present in a surrounding area, and a first threshold value that fluctuates according to the output value. Accordingly, when the output value gradually fluctuates due to factors over time such as adhesion of filth onto the surrounding area of the liquid leakage sensor, the first threshold value also gradually fluctuates in accordance with the fluctuation of the output value, and thus, false detection that a liquid is leaking can be suppressed. Therefore, according to the above, false detection can be suppressed regardless of use over a long period of time of the liquid leakage detector.

[0007]

In a liquid leakage detector according to a separate aspect, the first threshold value may fluctuate according to a moving average of the output value. When the output value fluctuates according to factors over time, the output value gradually fluctuates. In this case, a difference is maintained between the output value and the first threshold value that fluctuates according to a moving average of the output value. Accordingly, false detection can be suppressed by the output value that is fluctuated according to factors over time reaching the first threshold value. Meanwhile, when the output value fluctuates due to a leakage of liquid, the output value suddenly fluctuates. In this case, fluctuation of the output value occurs rapidly with respect to the first threshold value that fluctuates smoothly according to the moving average of the output value. Therefore, because the output value reaches the first threshold value when there is a leakage of liquid, the leakage of liquid can be detected with high precision. According to the above, false detection can be suppressed with high precision regardless of use over a long period of time of the liquid leakage detector.

[0008]

In a liquid leakage detector according to a separate aspect, the output value may be a measured value of the electrical resistance. In this case, because a fluctuation in the output value due to factors over time such as adhesion of filth and fluctuation in the output value at the time when a liquid has leaked can be detected with high precision, false detection can be suppressed regardless of use over a long period of time of the liquid leakage detector.

[0009]

In a liquid leakage detector according to a separate aspect, the liquid leakage determining unit further sets a second threshold value defined to a predetermined value in advance regardless of the output value and determines the presence or absence of a leakage of the liquid by comparing the output value to the first threshold value and the second threshold value. When the output value fluctuates according to factors over time, the output value gradually fluctuates. In this case, a difference is maintained between the output value and the first threshold value that fluctuates according to the output value. Meanwhile, as a result of continuous gradual fluctuation of the output value due to factors over time, when the size of change in the output value becomes constant or greater, the liquid leakage detector may determine that the liquid has leaked. However, when the first threshold value fluctuates without limit according to the fluctuation of the output value, the liquid leakage detector will not determine that a liquid leakage has occurred without reaching the first threshold value regardless of whether the size of the change in the output value becomes constant or greater. Here, by setting the second threshold value to be a threshold value that can determine that a liquid has leaked even if the output value has not reached the first threshold value allows detection of a leakage of liquid at an appropriate timing without dependency on the first threshold value. Therefore, according to the above, false detection can be suppressed with high precision regardless of use over a long period of time of the liquid leakage detector.

[0010]

In a liquid leakage detector according to a separate aspect, the first threshold value may be constant without depending on the output value for a predetermined time period after first detecting an amount of liquid present in a surrounding area by the liquid leakage detector. In this case, false detection of liquid leaking can be suppressed in a time period where there is a large error difference in output values immediately after the liquid leakage sensor first outputs the output value regardless of whether liquid has not leaked in a surrounding area of the liquid leakage sensor.

[0011]

In a liquid leakage detector according to a separate aspect, the second threshold value may be adjustable. In this case, because a fluctuation in the output value due to factors over time such as adhesion of filth and fluctuation in the output value at the time when a liquid has leaked can be detected with high precision, false detection can be suppressed regardless of use over a long period of time of the liquid leakage detector.

[0012]

In a liquid leakage detector according to a separate aspect, the liquid leakage determining unit, after determining the presence of a leakage of the liquid, further sets a return threshold for determining that the leak is no longer present, and determines whether a leak is no longer present by comparing the output value to the return threshold; and the return threshold may fluctuate according to the first threshold value. In this case, it is possible to set an appropriate return threshold value with respect to the fluctuating first threshold value. Through this, after leaked in a surrounding area of the liquid leakage sensor, the fact of the leakage of the liquid being no longer present can be determined with high precision when the leaked liquid is removed.

[0013]

A method for detecting liquid leakage according to one aspect of the present invention includes: a step in which a liquid leakage sensor outputs an output value according to an amount of a liquid present in a surrounding area; a step in which the output value output from the liquid leakage sensor is compared to a first threshold value that fluctuates according to the output value; and a step for determining the presence or absence of a leakage of the liquid based on the comparison.

[0014]

With the method for detecting liquid leakage thereof, the presence or absence of a leakage of a fluid is determined using the liquid leakage determining unit to compare the output value, output from the liquid leakage sensor, according to the amount of liquid present in a surrounding area, and a first threshold value that fluctuates according to the output value. Accordingly, when the output value gradually fluctuates due to factors over time such as adhesion of filth onto the surrounding area of the liquid leakage sensor, the first threshold value also gradually fluctuates in accordance with the fluctuation of the output value, and therefore, false detection that a liquid is leaking can be suppressed. Therefore, according to the above, false detection can be suppressed regardless of use over a long period of time of the liquid leakage detector. EFFECT OF THE INVENTION

[0015]

According to the present invention, false detection can be suppressed regardless of use over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]

FIG. 1 is a schematic diagram illustrating one embodiment of the liquid leakage detector according to the present invention.

FIG. 2 is a diagram for describing a method for detecting liquid leakage based on a first threshold value.

FIG. 3 is a diagram for describing a method for detecting liquid leakage based on a second threshold value.

EMBODIMENTS OF THE INVENTION

[0017]

Preferred embodiments of the liquid leakage detector according to the present invention are described below in detail with reference to drawings.

[0018]

FIG. 1 is a schematic diagram illustrating one embodiment of the liquid leakage detector according to the present invention. When a liquid leakage detector 1 disposed on a floor or the like of a building detects leakage of a liquid, it alerts a user that a leak has been detected. With this embodiment in particular, the liquid leakage detector 1 detects leakage of a conductive liquid such as, for example, tap water, seawater, industrial wastewater, solvents, and the like. The liquid leakage detector 1 includes an electrode portion 2, a main body 3, and a power supply unit 4 as illustrated in FIG. 1.

[0019]

The electrode portion 2, together with the output value computing unit 5 incorporated into the main body 3, configures the liquid leakage sensor 7. The electrode 2 includes electrodes 2a and 2b disposed in a separated manner. More specifically, the electron portion 2 forms, for example, a flat and substantially cylindrical shape, with the electrodes 2a and 2b having a long and thin shape curved along the outer periphery disposed separately on the outer peripheral side of the bottom surface. A cable 10 electrically connects the electrode portion 2 to the output value computing unit 5 incorporated into the main body 3, and power is supplied through the cable 10 from the main body 3 side. The output value computing unit 5 calculates an electrical resistance based on a drop in voltage between the electrodes 2a and 2b of the electrode portion 2 and outputs a measured value of the electrical resistance as an output value Rl to a liquid leakage determining unit 6 incorporated into the main body 3. The output value Rl fluctuates according to an amount of liquid particularly present between the electrodes 2a and 2b surrounding the electrode portion 2.

[0020]

The main body 3 is provided with a microprocessor within, for example, a box shaped casing, and the microprocessor is used for carrying out processing for, for example, liquid leakage determination and sensor voltage control. Further, the main body 3 has an input unit for inputting settings into the liquid leakage detector 1 , an information display unit for displaying the presence or absence of, for example, leakage water, and a buzzer for alerting that there is leakage water. The input unit is configured of a rotary switch, but a push button type or a volume type switch may be used.

[0021]

The microprocessor includes the output value computing unit 5 to calculate the electrical resistance from a drop in voltage between the electrodes 2a and 2b of the electrode portion 2, and the liquid leakage determining unit 6 to determine the presence or absence of a leakage of liquid from the output value Rl output from the output value computing unit 5. The liquid leakage determining unit 6 can set a threshold value to compare with the output value Rl and determine the presence or absence of a leak by operating the input unit. Similarly, a separate threshold value can be set in the liquid leakage determining unit 6 to determine, after a leak has already been determined, whether that leak is no longer present.

[0022]

The power supply unit 4 has a plug 8 for connecting to an external power source, and an AC/DC converter 9 electrically connected to the plug 8 by the cable 10. The AC/DC converter 9 converts AC 100 V supplied externally via the plug 8 to DC 12 V. Further, the AC/DC converter 9 is electrically connected to the main body 3 by the cable 10 to supply DC 12 V to the main body 3.

[0023]

Next, one example of a method for measuring electrical resistance using the liquid leakage sensor 7 will be described. However, the following measurement method is merely one example, and the number of seconds and the like described below may be appropriately modified to conduct measurement by a different measurement method.

[0024] Respective square waves of potentials of 5V and OV are repeatedly applied at a cycle of 1.0 seconds to the electrodes 2a and 2b of the liquid leakage sensor 7. After respectively applying a voltage of 5V for a period of 0.5 seconds to the electrodes 2a and 2b, OV is applied for 0.5 seconds. Further, with the electrodes 2a and 2b, the phases of the applied square waves are offset by 0.5 seconds, and when a voltage of 5V is applied to the electrode 2a, the electrode 2b is OV. Meanwhile, when the electrode 2a is 0V, a voltage of 5 V is applied to the electrode 2b.

[0025]

The liquid leakage sensor 7 outputs the electrical resistance for when a voltage of 5 V is applied to the electrode 2a to the liquid leakage determining unit 6 as the output value Rl . Similarly, the electrical resistance for when the voltage of 5 V is applied to the electrode 2b is output to the liquid leakage determining unit 6 as the next output value Rl . In this manner, the output value Rl of the electrical resistance between the electrodes 2a and 2b is output to the liquid leakage determining unit 6 every 1.0 seconds.

[0026]

Next, descriptions will be given of the various threshold values set by the liquid leakage determining unit 6.

[0027]

With the liquid leakage determining unit 6, as illustrated in FIG. 2 and FIG. 3, a first threshold value SI and a second threshold value S2 are set as thresholds for determining the presence or absence of water leakage by comparing the electrical resistance between the electrodes 2a and 2b output from the liquid leakage sensor 7. Note that, in FIG. 2 and FIG. 3, the vertical axis represents electrical resistance and the horizontal axis represents the passage of time. Furthermore, an alert period A represented by the rectangular shape in the drawing represents a time period in which a water leakage is detected by the liquid leakage detector 1 and an alert by a buzzer or the like disposed in the main body 3 is issued to notify to the effect that there is a water leakage.

[0028]

In this embodiment, the first threshold value SI is set to a value of one of either a fluctuation value S la or a reference value Sib, and here, the smaller of the two values of the fluctuation value Sla and the reference value Sib is employed as the first threshold value SI . The fluctuation value Sla, favored to be the first threshold value SI, fluctuates based on the output value Rl output from the liquid leakage sensor 7 to the liquid leakage determining unit 6 as illustrated in FIG. 2 and FIG. 3. Accordingly, when the fluctuation value S 1 a is used as the first threshold value S 1 , the first threshold value S 1 fluctuates according to the output value Rl . Here, it is preferable that the fluctuation value Sla (the first threshold value SI) is a value that does not fluctuate in order to perfectly follow based on the real-time fluctuation of the output value Rl . That is, as shown in FIG. 2, the output value Rl fluctuates in small increments even when a leakage has not occurred and suddenly fluctuates significantly when a conditions occurs in which a leak should be determined (see output value Rl in the location indicated by A). When the fluctuation value Sla (the first threshold value SI) perfectly follows the output value Rl, detection of the leakage may be delayed due to the fluctuation value Sla (the first threshold value SI) also fluctuating when following the output value Rl even though the output value Rl suddenly fluctuates at the occurrence of a leakage. Therefore, it is preferable that the fluctuation value Sla (the first threshold value SI) is set so as to follow a smoothed or averaged value of the fluctuation of the output value Rl .

[0029]

For example, the fluctuation value Sla (the first threshold value SI) may fluctuate according to a moving average R2 of the output value Rl . The fluctuation value Sla (the first threshold value SI) may be a value calculated by subtracting a predetermined value from the moving average R2 of the output value Rl, or it may be a value obtained by multiplying the moving average R2 by a predetermined coefficient. Further, a corrected moving average, simple moving average, weighted moving average, index moving average, and the like may be used as the moving average R2. For example, when setting the fluctuation value Sla (the first threshold value SI) based on a moving average R2 of the output value Rl, the liquid leakage determining unit 6 calculates the moving average R2 according to the following formula (1) based on the output value Rl . Whereas, Rl (n) is the nth output value and R2 (n) is the nth moving average. Further, a is a coefficient indicating smoothing of the moving average and is a value not less than 0 and not greater than 1. The liquid leakage determining unit 6 sets a value in which a predetermined value is subtracted from the moving average R2 as the fluctuation value Sla (the first threshold value SI).

R2 (n) = a x Rl (n) + (1-a) x R2 (n-1) ... (1)

Whereas,

R2 (0) = Rl (0)

[0030]

The reference value Sib (the first threshold value SI) is a value set as a safe reference in which it may be determined that there is no leakage. That is, the reference value Sib (the first threshold value SI) is set to a value where there is no problem in determining that there is no leakage as long as at least the output value Rl does not reach the reference value Sib. The reference value Sib (the first threshold value SI) may be set as a value obtained by adding a predetermined value to the second threshold value S2 described below. For example, the reference value Sib (the first threshold value SI) is set to a value lower than the fluctuation value Sla for when it is dry between the electrodes 2a and 2b of the electrode portion 2. In this embodiment, the reference value Sib does not fluctuation with the passage of time. Note that, the reference value Sib (the first threshold value SI) may be set to a value that is obtained by multiplying the second threshold value S2 by a predetermined coefficient. Moreover, a value determined to be unrelated to the second threshold value S2 may be employed as the reference value Sib (the first threshold SI). Further, the reference value Sib (the threshold value SI) may be a value that changes over time according to a pattern unrelated to the output value Rl . For example, the reference value Sib (the threshold value SI) may be a value that increases or reduces at a predetermined slope. Note that, in the example shown in FIG. 2 and FIG. 3, a reference value Sib is used as the first threshold value SI when the fluctuation value Sla is larger than the reference value Sib, and the fluctuation value Sla is used as the first threshold value SI at a timing in which the fluctuation value SI is equal to or falls below the reference value Sib. However, the timing for the first threshold value SI to switch from the reference value Sib to the fluctuation value Sla is not limited. For example, the fluctuation value Sla may automatically switch to the first threshold value SI after a predetermined time period has elapsed after the liquid leakage sensor 7 first detects an amount of fluid present in the surrounding area.

[0031]

The second threshold value S2, as shown in FIG. 2 and FIG. 3, is set to a predetermined value that does not depend on the output value Rl . The output value Rl gradually decreases due to the time factor, but, for example, if the output value Rl does not suddenly decrease as in the peak PI in FIG. 2, the output value Rl does not reach the first threshold SI described above. In this case, even if the output value Rl has decreased to a level at which it should be determined that a leak has occurred, there is a possibility that the leak cannot be detected by the first threshold value SI because the output value Rl has not dropped suddenly. The second threshold value S2, under this type of circumstance, is a threshold in order to detect the occurrence of a leakage regardless of the first threshold value S 1. The second threshold value S2 is set to a value low enough to allow

determination that a leakage has occurred immediately when the output value Rl has reached such a value (regardless of factors over time, fluctuation in a spiking output value Rl, and the like). For example, the second threshold value S2 is at least set to a value lower than the fluctuation value Sla for when the area between the electrodes 2a and 2b of the electrode portion 2 is dry and is set to a value lower than the reference value Sib. The second threshold value S2, although it does not fluctuate over time, can be freely set by operating the rotary switch, which is the input unit, provided on, for example, the main body 3.

[0032]

Further, return threshold values S3, S4 are set in the liquid leakage determining unit 6 to determine, after a water leakage has been determined by the first threshold value SI and the second threshold value S2, that the water leakage is no longer present. When it is determined that there is a water leakage by the output value Rl being equal to or lower than the first threshold value SI, the return threshold value S3 become effective.

Meanwhile, when it is determined that there is a water leakage by the output value Rl being equal to or lower than the second threshold value S2, the return threshold value S4 becomes effective.

[0033]

The return threshold value S3, as shown in FIG. 2, is set to a value larger than the first threshold value SI (namely, the output value Rl when a leak is detected) that is in place when the output value Rl arrives at the first threshold value SI . For example, the return threshold value S3 may be a value obtained by adding a predetermined value C 1 to the value of the first threshold value SI when the output value Rl reaches the first threshold value S 1. Further, the return threshold value S3 may be a value obtained by multiplying the value of the first threshold value S 1 by a predetermined coefficient when the output value Rl reaches the first threshold value SI . In this manner, the return threshold value S3 is set based on the first threshold value SI . Particularly, as shown in FIG. 2, when the leak is detected in a region where the fluctuation value Sla is used as the first threshold value SI, the return threshold value S3 is set based on the fluctuating first threshold value S 1. In this case, the return threshold value S3 is not defined to be a fixed value, but the return threshold value S3 is also set to be a fluctuating value according to the fluctuation of the first threshold value SI . Note that the return threshold value S3 may be allowed to change over time according to the length of the use period.

[0034]

The return threshold value S4, as shown in FIG. 3, is set to be a value greater than the value of the second threshold value S2. For example, the return threshold value S4 may be a value that is obtained by adding a predetermined value C2 to the value of the second threshold value S2. Further, the return threshold value S4 may be a value that is obtained by multiplying the value of the second threshold value S2 by a predetermined coefficient. Note that the return threshold value S4 may be allowed to change over time according to the length of the use period. [0035]

Furthermore, a case will be described with reference to FIG. 2 wherein the liquid leakage determining unit 6 determines a liquid leakage based on the first threshold value SI . In the liquid leakage detector 1, as described above, the output value Rl of the electrical resistance gradually fluctuates according to factors over time such as the adhesion of filth around the surrounding area of, for example, the electrode portion 2. In other words, because the electrode 2a and the electrode 2b are disposed separately with air therebetween as an insulator, conductive water or the like mixes with dust and enters between the electrodes 2a and 2b, and the output value Rl of the electrical resistance and the moving average R2 between the electrodes 2a and 2b gradually reduce. In this case, the false detection of water leakage can be suppressed by the output value Rl being reduced by factors over time such as the accumulation of dust (even if water is not actually leaking) because the first threshold value SI (fluctuation value SI a) is gradually reduced in accordance with the reduction of the moving average R2. Meanwhile, as illustrated with peak PI in FIG. 2, when water leakage actually occurs, the output value Rl rapidly decreases due to the gap between the electrodes 2a and 2b short circuiting by conductive water or the like. Therefore, the output value Rl reaches the first threshold value SI (fluctuation value SI a) faster than the first threshold value SI (fluctuation value SI a) decreases in accordance with the decrease of the moving average R2 of the output value Rl . By this, the liquid leakage determining portion 6 determines there is a water leakage and notifies the user by a buzzer or the like. Thereafter, after the user wipes up liquid leaked in the surrounding area of the electrode portion 2 or the like, the electrical resistance between the electrodes 2a and 2b increases again and the output value Rl increases. Next, when the output value Rl increases to a value that is the sum of the value of the first threshold value SI when the output value Rl reaches the first threshold value SI and the predetermined value CI, in other words, when the output value Rl increases to the return threshold S3, the liquid leakage determining unit 6 determines that the water leakage is gone and the notification by a buzzer or the like ceases.

[0036]

Meanwhile, in a region where the reference value S lb is used as the first threshold value S 1 , it is not necessary to determine that there is a water leakage because the output value Rl is still large even if the output value Rl fluctuates greatly (for a reason other than water leakage) and reaches the fluctuation value Sla as illustrated with the peak P2 in FIG. 2. According to the present embodiment, when this happens, a false detection can be suppressed because it is not determined that there is a water leakage due to the output value Rl not reaching the reference value Sib used as the first threshold value SI . [0037]

Further, a case will be described with reference to FIG. 3 wherein the liquid leakage determining unit 6 determines a liquid leakage based on the second threshold value S2. As described above, when the output value Rl of the electrical resistance and the moving average R2 between the electrodes 2a and 2b are gradually reduced due to factors over time, the first threshold value SI (fluctuation value SI a) is also gradually reduced in accordance with the decreasing of the moving average R2. Because of this, when a peak such as that illustrated as peak P2 in FIG. 2 does not occur in the output value Rl, the output value Rl does not reach or go lower than the first threshold value SI (fluctuation value SI a), and the liquid leakage determining unit 6 does not determine that there is a water leakage. However, when the output value Rl is reduced to a value equal to that of the output value Rl when there actually is a water leakage, it is preferable to determine that there is a water leakage even if the output value Rl does not reach the first threshold value SI (fluctuating value SI a). By setting a second threshold value S2 that does not fluctuate over time, it can be determined that there is a water leakage by the output value Rl reaching the second threshold value S2 even if the output value Rl does not reach the first threshold value SI (fluctuation value SI a) because it has gradually decreased. In this case, the liquid leakage determining portion 6 determines there is a water leakage and notifies the user by a buzzer or the like. Afterwards, after the user wipes up liquid leaked in the surrounding area of the electron portion 2 or the like, the electrical resistance between the electrodes 2a and 2b increases again and the output value Rl increases. Next, when the output value Rl increases to a value that is the sum of second threshold value S2 and the predetermined value C2, in other words, the return threshold S4, the liquid leakage determining unit 6 determines that the water leakage is no longer present and the notification by a buzzer or the like ceases.

[0038]

As described above, the liquid leakage detector 1 compares, using the liquid leakage determining unit 6, the output value Rl of the electrical resistance that is based on the amount of liquid present in the surrounding area and the first threshold value S 1 that fluctuates in accordance with the value Rl, both output from the liquid leakage sensor 7, and determines the presence or absence of liquid leakage. Therefore, when the output value Rl gradually fluctuates according to factors over time such as the adhesion of filth around the surrounding area of the liquid leakage sensor 7, a false detection of liquid leaking can be suppressed because the first threshold value S 1 also gradually fluctuates in accordance with the fluctuation of the output value Rl . Therefore, a false detection can be suppressed even if the liquid leakage detector 1 is used over a long period of time. [0039]

Furthermore, the first threshold value S 1 fluctuates in accordance with the moving average of the output value Rl . When the output value Rl fluctuates according to factors over time, the output value Rl gradually fluctuates. In this case, the difference between the fluctuation value Sla that fluctuates according to the moving average R2 of the output value Rl and the output value Rl is maintained. Therefore, false detection by the output value Rl that fluctuates according to factors over time can be suppressed. Meanwhile, when the output value Rl fluctuates according to leakage of liquid, the output value Rl rapidly fluctuates. In this case, fluctuation of the output value Rl is faster when compared to the fluctuation value Sla that smoothly fluctuates according to the moving average R2 of the output value Rl . Therefore, when there is a leakage of liquid, the leakage of liquid can be accurately detected because the output value Rl reaches the fluctuation value Sla. Therefore, false detection can be suppressed with high precision regardless of use over a long period of time of the liquid leakage detector 1.

[0040]

Further, the output value Rl is a measured value of the electrical resistance.

Because of this, a false detection can be suppressed even if the liquid leakage detector 1 is used over a long period of time because the fluctuation of the output value Rl by factors over time such as the adhesion of filth and the fluctuation of the output value Rl when liquid has leaked can be accurately determined.

[0041]

Furthermore, the liquid leakage determining unit 6 further sets a second threshold value S2 stipulated to a predetermined value in advance regardless of the output value Rl and determines the presence or absence of a leakage of the liquid by comparing the output value Rl to the first threshold value SI and the second threshold value S2. When the output value Rl fluctuates according to factors over time, the output value Rl gradually fluctuates. In this case, the difference between the fluctuation value Sla that fluctuates according to the moving average R2 of the output value Rl and the output value Rl is maintained. Meanwhile, when the degree of decrease of the output value Rl has become constant or greater after the output value Rl has continued to gradually fluctuate according to factors over time, it may be necessary to determine that there is a leakage of liquid. However, if the fluctuation value Sla is caused to endlessly fluctuate according to the fluctuation of the output value Rl, the output value Rl does not reach the fluctuation value Sla even though the degree of the decrease in the output value Rl has reached a constant level or greater, and it is not determined that there is a leakage of liquid. Here, by setting a second threshold value S2 as a threshold value that can determine that there is a leakage of liquid even if the output value Rl does not reach the fluctuation value SI a, a leakage of liquid can be detected at the proper timing regardless of the first threshold value S 1.

Therefore, false detection can be suppressed with high precision regardless of use over a long period of time of the liquid leakage detector 1.

[0042]

Further, the first threshold value S 1 is fixed in a predetermined period of time regardless of the output value Rl after the liquid leakage sensor 7 begins to detect an amount of liquid present in a surrounding area. Because of this, during a period of time when errors of the output value Rl are large directly after the liquid leakage sensor 7 begins to output the output value Rl, a false detection that there is a leakage of liquid can be suppressed even though there is no leakage of liquid in the surrounding area of the liquid leakage sensor 7.

[0043]

Moreover, the second threshold value S2 is adjustable. Because of this, a false detection can be suppressed even if the liquid leakage detector 1 is used over a long period of time because the fluctuation of the output value Rl due to factors over time such as the adhesion of filth and the fluctuation of the output value Rl when liquid has leaked can be accurately determined.

[0044]

Further, the liquid leakage determining unit 6, after determining the presence of a liquid leakage, further sets the return threshold S3 for determining that the leak is no longer present and determines whether a leak is no longer present by comparing the output value Rl to the return threshold S3; and the return threshold S3 fluctuates according to the first threshold value S 1. Thus it becomes possible to set a proper return threshold S3 with respect to the fluctuating first threshold value SI . Therefore, by removing the leaked liquid when liquid has leaked in the surrounding area of the liquid leakage sensor 7, it can be accurately determined that the leakage of liquid is no longer present.

[0045]

Further, with the method for detecting a liquid leakage according to the present embodiment, with the liquid leakage detector 1 , the liquid leakage sensor 7 measures the electrical resistance between the electrodes 2a and 2b disposed separately, and outputs the output value Rl . Furthermore, the liquid leakage determining unit 6 compares the output value Rl output from the liquid leakage sensor 7 to a first threshold value SI that fluctuates according to the output value Rl . Next, the presence or absence of water leakage is determined based on the comparison of the output value Rl and the first threshold value SI . In this manner, the output value Rl that is based on the amount of liquid that is present in the surrounding area and the first threshold value S 1 that fiuctuates in accordance with the value Rl, both output from the liquid leakage detecting sensor 7, are compared using the liquid leakage determining unit 6, and the presence of liquid leakage is determined. Therefore, when the output value Rl gradually fluctuates according to factors over time such as the adhesion of filth around the surrounding area of the liquid leakage detecting sensor 7, false detection of liquid leaking can be suppressed because the first threshold value S 1 also gradually fluctuates in accordance with the fluctuation of the output value Rl . Therefore, a false detection can be suppressed even if the liquid leakage detector 1 is used over a long period of time.

[0046]

The present invention is not limited to the above embodiment. For example, in the above embodiment, the liquid leakage sensor 7 has electrodes 2a and 2b disposed separately, and detects the leakage of a conductive liquid such as water by measuring the electrical resistance between the electrodes 2a and 2b. However, the liquid leakage sensor 7 can output, for example, an electrostatic capacitance or a light transmittance between the electrodes as the output value Rl . In this manner, the leakage of a non-conductive liquid such as oil can be detected.

[0047]

Also, in the above embodiment, the output value Rl is the electrical resistance between the electrodes 2a and 2b, and the liquid leakage determining unit 6 determines that there is a leakage when the output value Rl falls below the first threshold value SI or the second threshold value S2. However, for example, when using a value that is obtained by performing calculation processing on the electrical resistance between the electrodes 2a and 2b as the output value Rl, or using something other than the electrical resistance as the output value Rl, the liquid leakage determining unit 6 may determine that there is a leakage when the output value Rl rises above the first threshold value SI or the second threshold value S2.

[Reference Numerals]

[0048]

1 Liquid leakage detector, 6... Liquid leakage determining unit, Ί ... Liquid leakage sensor, Rl ... Output value, R2... Moving average, SI ... First threshold value, S2...

Second threshold value, S3... Return threshold

Claims

What is claimed is:

1. A liquid leakage detector comprising:

a liquid leakage sensor that outputs an output value according to an amount of a liquid present in a surrounding area; and

a liquid leakage determining unit that sets a first threshold value and determines the presence or absence of a leakage of the liquid by comparing the output value output from the liquid leakage sensor to the first threshold value; wherein the first threshold value fluctuates according to the output value.

2. The liquid leakage detector according to claim 1, wherein the first threshold value fluctuates according to a moving average of the output value.

3. The liquid leakage detector according to claim 1 or 2, wherein the output value is a measured value of the electrical resistance.

4. The liquid leakage detector according to any one of claims 1 to 3, wherein the liquid leakage determining unit further sets a second threshold value defined to a predetermined value in advance regardless of the output value and determines the presence or absence of a leakage of the liquid by comparing the output value to the first threshold value and the second threshold value.

5. The liquid leakage detector according to any one of claims 1 to 4, wherein the first threshold value is fixed in a prescribed period of time regardless of the output value after the liquid leakage sensor begins to detect an amount of the liquid present in a surrounding area.

6. The liquid leakage detector according to claim 4, wherein the second threshold value is adjustable.

7. The liquid leakage detector according to any one of claims 1 to 6, wherein the liquid leakage determining unit, after determining the presence of a leakage of the liquid, further sets a return threshold for determining that the leak is no longer present, and determines whether a leak is no longer present by comparing the output value to the return threshold; and the return value fluctuates according to the first threshold value.

8. A method for detecting liquid leakage, comprising: a step for a liquid leakage sensor to output an output value according to an amount of a liquid present in a surrounding area;

a step for comparing the output value output from the liquid leakage sensor to a first threshold value that fiuctuates according to the output value; and

a step for determining the presence or absence of a leakage of the liquid based on the comparison.