Water leakage detection circuit, water leakage detection system

Abstract

A first resistor R1 and a switch S1 are connected in series between a first electrode 11 of a water leakage sensor 10 and a first fixed potential. A control unit 21 intermittently operates the switch S1, extending an ON period for the switch S1 for a predetermined length of time when the voltage of the first electrode 11 is on a second fixed potential side of a water leakage detection threshold voltage during the ON period of the switch S1 and confirming a water leakage determination when the voltage of the first electrode 11 is continuously on the second fixed potential side of the water leakage detection threshold voltage for the extended period.

Description

Leakage detection circuit, leakage detection system

[0001] The present disclosure relates to a leakage detection circuit and a leakage detection system connected to a leakage sensor.

[0002] A general leakage sensor detects leakage by arranging two electrodes and detecting that a conductive liquid (such as water) penetrates between the electrodes to form a conductive path and the resistance value between the electrodes decreases (see, for example, Patent Document 1).

[0003] In a leakage sensor, it is necessary to apply a bias voltage between two electrodes. However, in a high-humidity environment, if the bias voltage is continuously applied between the electrodes, the electrodes are likely to corrode. Also, it is conceivable to connect a disconnection detection resistor between the electrodes to distinguish between the dry state and disconnection. In that case, if the bias voltage is continuously applied between the electrodes, the power consumption increases. As countermeasures against these, it is conceivable to apply the bias voltage intermittently instead of constantly applying it between the two electrodes.

[0004] Japanese Patent Application Laid-Open No. 2021-131339

[0005] When moisture begins to adhere to the electrodes, the parasitic capacitance between the electrodes increases. When the parasitic capacitance between the electrodes increases, the setting time (settling time) of the monitoring voltage becomes longer. When the leakage sensor is driven intermittently, there is a risk of false determination because the monitoring voltage does not settle during the energization period. If the intermittent drive period is lengthened, the risk of false determination can be reduced, but since the frequency of fluctuation of the potential difference between the electrodes decreases, the effect of suppressing the progress of electrolytic corrosion becomes smaller.

[0006] The present disclosure has been made in view of such circumstances, and its object is to provide a technique for accurately determining the presence or absence of leakage while suppressing deterioration of the leakage sensor.

[0007] To solve the above problems, a water leak detection circuit according to one aspect of the present disclosure comprises: a first electrode of a water leak sensor having a first electrode that conducts to a first fixed potential and a second electrode that conducts to a second fixed potential, wherein the insulation resistance between the first electrode and the second electrode decreases when a conductive liquid enters between the first electrode and the second electrode; a first resistor connected between the first electrode of the water leak sensor and the first fixed potential; a switch connected in series with the first resistor between the first electrode of the water leak sensor and the first fixed potential; and a control unit that detects the voltage of the first electrode of the water leak sensor and determines that there is a water leak if the detected voltage of the first electrode is located on the second fixed potential side of the water leak detection threshold voltage. The control unit intermittently operates the switch, and if the voltage of the first electrode is located on the second fixed potential side of the water leak detection threshold voltage during the switch's ON period, the ON period of the switch is extended for a predetermined time, and if the voltage of the first electrode remains on the second fixed potential side of the water leak detection threshold voltage for the extended period, the determination of a water leak is confirmed.

[0008] According to this disclosure, it is possible to determine the presence or absence of a water leak with high accuracy while suppressing the deterioration of the water leak sensor.

[0009] This figure shows a cross-sectional view of a linear water leak sensor. This figure is for explaining a water leak detection system according to a comparative example. This figure is for explaining a water leak detection system according to Embodiment 1. This figure shows an example of the relationship between the amount of droplets deposited between electrodes and the detected voltage in graph form. This figure shows the water leak sensor of Figure 3 with parasitic capacitance added. This figure shows an example of the behavior of the detected voltage in the case of no parasitic capacitance, with parasitic capacitance but no water leak, and with parasitic capacitance but water leak, in graph form. This is a flowchart for explaining the operation flow of the water leak detection system according to Embodiment 1. This figure is for explaining a water leak detection system according to Embodiment 2.

[0010] Figure 1 shows a cross-sectional view of a linear water leak sensor 10. The linear water leak sensor 10 is highly flexible and can be installed in various shapes and sizes. The linear water leak sensor 10 comprises a first electrode 11, a second electrode 12, a first internal braid 13a, a second internal braid 13b, and an external braid 13c. For example, soft copper stranded wire is used for the first electrode 11 and the second electrode 12. The first electrode 11 is covered by the first internal braid 13a, the second electrode 12 is covered by the second internal braid 13b, and furthermore, the first internal braid 13a and the second internal braid 13b are covered by the external braid 13c. For example, special water-absorbing plastic fibers are used for the first internal braid 13a, the second internal braid 13b, and the external braid 13c. The first internal braid 13a, the second internal braid 13b, and the external braid 13c have sufficient insulating performance when dry. The first electrode 11, covered by the first internal braid 13a, and the second electrode 12, covered by the second internal braid 13b, are arranged spirally within the external braid 13c.

[0011] Figure 2 is a diagram illustrating a water leak detection system 1 according to a comparative example. The water leak detection system 1 comprises a water leak sensor 10 and a water leak detection circuit 20. The water leak detection circuit 20 comprises a control unit 21.

[0012] The first electrode 11 of the water leak sensor 10 is installed to conduct to the high-side reference potential VDD (hereinafter referred to as the power supply potential VDD). The second electrode 12 of the water leak sensor 10 is installed to conduct to the low-side reference potential GND (hereinafter referred to as the ground potential GND). The first electrode 11 and the second electrode 12 are connected via connector CN1 to wiring connected to the board on which the water leak detection circuit 20 is mounted. Hereinafter, this specification assumes an example where the power supply potential VDD is set to 5V.

[0013] A first resistor R1 is connected between the power supply potential VDD and the first electrode 11. The insulation resistance Rs between the first electrode 11 and the second electrode 12 and the first resistor R1 constitute a resistive voltage divider circuit. When a conductive liquid such as water enters between the first electrode 11 and the second electrode 12, the insulation resistance Rs decreases. The greater the amount of water dripped in, the greater the decrease in the insulation resistance Rs between the electrodes. The voltage division point N1 between the first resistor R1 and the insulation resistance Rs is connected to the AD port of the control unit 21.

[0014] The control unit 21 is composed of a microcontroller. The microcontroller has a built-in A / D converter, which converts the analog voltage input to the AD port into a digital value. The A / D converter may also be external. In that case, the voltage of the first electrode 11 (hereinafter referred to as the detected voltage V1), which is the voltage at the voltage division point N1, is converted into a digital value by the external A / D converter and then input to the microcontroller.

[0015] The control unit 21 determines whether or not there is a water leak based on the detected voltage V1. If the detected voltage V1 is lower than a preset water leak detection threshold voltage Vth1, the control unit 21 determines that there is a water leak, and if the detected voltage V1 is equal to or greater than the water leak detection threshold voltage Vth1, it determines that it is normal (no water leak).

[0016] As described above, if current is constantly flowed between the first electrode 11 and the second electrode 12, power consumption increases, and the first electrode 11 and the second electrode 12 become more susceptible to corrosion.

[0017] Figure 3 is a diagram illustrating the water leak detection system 1 according to Embodiment 1. The differences from the water leak detection system 1 according to the comparative example shown in Figure 2 will be explained below. In Embodiment 1, a switch S1 is connected in series with a first resistor R1 between the first electrode 11 of the water leak sensor 10 and the power supply potential VDD. In Embodiment 1, a P-channel semiconductor switch (more specifically, a P-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)) is used for the switch S1. The source terminal of the P-channel MOSFET is connected to the power supply potential VDD, the drain terminal is connected to the first resistor R1, and the gate terminal is connected to the drive port of the control unit 21. Note that an IGBT (Insulated Gate Bipolar Transistor), a bipolar transistor, or a relay may be used instead of the MOSFET.

[0018] The control unit 21 operates the switch S1 intermittently. The control unit 21 may intermittently drive the switch S1 with a period of, for example, 250 ms. When the control unit 21 controls the switch S1 to the ON state, it lowers the gate voltage of the switch S1 to a value greater than or equal to the power supply potential VDD. For example, it controls the gate voltage to 0V. When the control unit 21 controls the switch S1 to the OFF state, it raises the gate voltage of the switch S1 to a value greater than or equal to the power supply potential VDD. For example, it controls the gate voltage to 5V.

[0019] A second resistor R2 connects the first electrode 11 and the second electrode 12. The second resistor R2 is connected to detect a physical disconnection of the first electrode 11 or the second electrode 12, or a disconnection of the connector CN1. Hereinafter, both physical disconnections and disconnections of the connector CN1 will be collectively referred to simply as disconnections. When the second resistor R2 is not connected, both the dry state and the disconnection appear to the control unit 21 as the same high-impedance state. By connecting the second resistor R2, the impedance of the dry state can be reduced to the impedance of the disconnection.

[0020] When switch S1 is in the off position, the detected voltage V1 is 0V. When switch S1 is in the on position, the detected voltage V1 is defined as follows (Equation 1): V1 = R10 / (R1 + R10) * VDD ... (Equation 1) R10 = 1 / (1 / R2 + 1 / Rs)

[0021] Figure 4 is a graph illustrating an example of the relationship between the amount of liquid deposited between the electrodes and the detection voltage V1. The wire break detection threshold voltage Vth2 is set to a higher value than the water leak detection threshold voltage Vth1. In the example shown in Figure 4, the water leak detection threshold voltage Vth1 is set to approximately 1.5V, and the wire break detection threshold voltage Vth2 is set to approximately 3.8V.

[0022] As described above, with the second resistor R2 connected, the detection voltage V1 is maintained at approximately 3V even when the dripping volume "ml" is 0 or small, without sticking to the power supply potential VDD. The control unit 21 tentatively determines that there is a water leak if the detection voltage V1 is lower than the water leak detection threshold voltage Vth1. The control unit 21 determines that it is normal (no water leak) if the detection voltage V1 is within the range between the water leak detection threshold voltage Vth1 and the wire break detection threshold voltage Vth2. The control unit 21 determines that at least one of the first electrode 11 or the second electrode 12 is broken if the detection voltage V1 is higher than the wire break detection threshold voltage Vth2.

[0023] Figure 5 shows the leak sensor 10 in Figure 3 with a parasitic capacitance Cs added. When moisture adheres between the first electrode 11 and the second electrode 12, the parasitic capacitance Cs between the first electrode 11 and the second electrode 12 increases.

[0024] Figure 6 is a graph illustrating an example of the behavior of the detection voltage V1 in the following cases: when there is no parasitic capacitance Cs (X), when there is parasitic capacitance Cs but no water leakage (Y), and when there is parasitic capacitance Cs but water leakage (Z). When there is no parasitic capacitance Cs (X), the detection voltage V1 rises instantaneously when transitioning from the off period to the on period and exceeds the water leakage detection threshold voltage Vth1. On the other hand, when there is parasitic capacitance Cs (Y, Z), the rate of rise of the detection voltage V1 slows down, and it is not possible to exceed the water leakage detection threshold voltage Vth1 during the on period (e.g., 250 ms).

[0025] To address the delay in the rise of the detection voltage V1 due to the parasitic capacitance Cs, this embodiment introduces the following control. During the ON period of switch S1, if the detection voltage V1 is lower than the water leak detection threshold voltage Vth1, the control unit 21 extends the ON period of switch S1 by a predetermined time (for example, 750 ms). If the detection voltage V1 exceeds the water leak detection threshold voltage Vth1 during the extended ON period, the switch S1 is immediately turned OFF, and the system transitions to the normal intermittent operation state (Y). If the extended ON period continues while the detection voltage V1 remains lower than the water leak detection threshold voltage Vth1, the determination of water leakage is confirmed. Once the determination of water leakage is confirmed, the control unit 21 notifies the higher-level system (not shown) of an error, turns off switch S1, and stops the operation of the water leak detection system 1 (Z).

[0026] Figure 7 is a flowchart illustrating the operation flow of the water leak detection system 1 according to Embodiment 1. The control unit 21 operates the switch S1 intermittently (S10). At the end of the ON period, the control unit 21 compares the detected voltage V1 with the water leak detection threshold voltage Vth1 (S11). If the detected voltage V1 is lower than the water leak detection threshold voltage Vth1 (Y in S11), the control unit 21 switches the switch S1 to continuous ON operation (S16).

[0027] During continuous ON operation, the control unit 21 determines whether the detected voltage V1 has remained below the water leak detection threshold voltage Vth1 for a predetermined time (S17). If it has (Y in S17), the control unit 21 determines that there is a water leak (S18). If the detected voltage V1 exceeds the water leak detection threshold voltage Vth1 within the predetermined time (N in S17), it determines that there is no water leak and proceeds to step S10.

[0028] In step S11, if the detected voltage V1 is greater than or equal to the water leak detection threshold voltage Vth1 (N in S11), the control unit 21 determines whether the detected voltage V1 has exceeded the wire break detection threshold voltage Vth2 (S12). If it has exceeded it (Y in S12), the control unit 21 switches the switch S1 to continuous on operation (S13). During continuous on operation, the control unit 21 determines whether the detected voltage V1 has remained above the wire break detection threshold voltage Vth2 for a predetermined time (S14). If it has exceeded it (Y in S14), the control unit 21 determines that a wire break has occurred in the water leak sensor 10 (S15). In step S12, if the detected voltage V1 is less than or equal to the wire break detection threshold voltage Vth2 (N in S12), it is determined that there is no water leak and the system proceeds to step S10. In step S14, if the detected voltage V1 does not exceed the wire break detection threshold voltage Vth2 for a predetermined time (N in S14), it is determined that there is no water leakage, and the process proceeds to step S10. Note that steps S13 and S14 can be omitted.

[0029] Figure 8 is a diagram illustrating a water leak detection system 1 according to Embodiment 2. The water leak detection system 1 according to Embodiment 2 is an example in which the water leak sensor 10 is placed above the resistive voltage divider circuit. In Embodiment 2, the second electrode 12 of the water leak sensor 10 is installed to conduct to the power supply potential VDD. A first resistor R1 and a switch S1 are connected in series between the first electrode 11 of the water leak sensor 10 and the ground potential GND. In Embodiment 2, an N-channel semiconductor switch (more specifically, an N-channel MOSFET) is used for the switch S1. The source terminal of the N-channel MOSFET is connected to the ground potential GND, the drain terminal is connected to the first resistor R1, and the gate terminal is connected to the drive port of the control unit 21.

[0030] When the control unit 21 controls switch S1 to the ON state, it raises the gate voltage of switch S1 to a value above the ground potential GND. For example, it controls the gate voltage to 5V. When the control unit 21 controls switch S1 to the OFF state, it lowers the gate voltage of switch S1 to below the ground potential GND. For example, it controls the gate voltage to 0V.

[0031] In Embodiment 2, the wire break detection threshold voltage Vth2 is set to a value lower than the water leak detection threshold voltage Vth1. The control unit 21 provisionally determines that there is a water leak if the detected voltage V1 is higher than the water leak detection threshold voltage Vth1. The control unit 21 determines that it is normal (no water leak) if the detected voltage V1 is within the range between the water leak detection threshold voltage Vth1 and the wire break detection threshold voltage Vth2. The control unit 21 determines that at least one of the first electrode 11 or the second electrode 12 is broken if the detected voltage V1 is lower than the wire break detection threshold voltage Vth2.

[0032] If the detected voltage V1 is higher than the water leak detection threshold voltage Vth1 during the ON period of switch S1, the control unit 21 extends the ON period of switch S1 for a predetermined time (for example, 750 ms or more). If the detected voltage V1 remains higher than the water leak detection threshold voltage Vth1 for the extended period, the control unit 21 confirms that a water leak is present. Once the control unit 21 confirms that a water leak is present, it notifies the higher-level system (not shown) of an error, turns off switch S1, and stops the operation of the water leak detection system 1.

[0033] Embodiments 1 and 2 can be summarized as follows: The first electrode 11 conducts to a first fixed potential via the first resistor R1 and switch S1. The second electrode 12 conducts to a second fixed potential. The control unit 21 provisionally determines that there is a water leak if the detected voltage V1 is located on the second fixed potential side of the water leak detection threshold voltage Vth1. The control unit 21 determines that it is normal (no water leak) if the detected voltage V1 is within the range between the water leak detection threshold voltage Vth1 and the wire break detection threshold voltage Vth2. The control unit 21 determines that at least one of the first electrode 11 or the second electrode 12 is broken if the detected voltage V1 is located on the first fixed potential side of the wire break detection threshold voltage Vth2.

[0034] The control unit 21, during the ON period of switch S1, extends the ON period of switch S1 by a predetermined time if the detected voltage V1 is located on the second fixed potential side of the water leakage detection threshold voltage Vth1. If the detected voltage V1 remains on the second fixed potential side of the water leakage detection threshold voltage Vth1 for the extended period, the control unit confirms that there is a water leak.

[0035] As described above, in embodiments 1 and 2, the switch S1 is operated intermittently. This suppresses the deterioration of the water leak sensor 10 and reduces the power consumption of the water leak detection system 1. In embodiments 1 and 2, if the detected voltage V1 is located on the second fixed potential side of the water leak detection threshold voltage Vth1, a provisional determination is made that there is a water leak, and the ON period of the switch S1 is extended. If the detected voltage V1 continues to be located on the second fixed potential side of the water leak detection threshold voltage Vth1 during the extended ON period, the determination that there is a water leak is confirmed. This eliminates the effect of the time constant increase due to the increase in parasitic capacitance Cs, and allows for highly accurate determination of the presence or absence of a water leak while suppressing the deterioration of the water leak sensor 10 through intermittent operation.

[0036] Furthermore, by connecting a second resistor R2 between the first electrode 11 and the second electrode 12, it is possible to clearly distinguish between a dry state and a broken wire simply by monitoring the detected voltage V1.

[0037] According to the circuit configuration of Embodiment 1, the detection voltage V1 can be designed with reference to the ground potential GND, thus simplifying circuit design. According to the circuit configuration of Embodiment 2, by using an N-channel MOSFET for the switch S1, power consumption due to on-resistance can be further reduced.

[0038] The present disclosure has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure.

[0039] A comparator for detecting water leaks and a comparator for detecting wire breaks may be installed between the pressure division point N1 and the microcontroller. The water leak detection comparator compares the detected voltage V1 with the water leak detection threshold voltage Vth1 and outputs the comparison result to the microcontroller. The wire break detection comparator compares the detected voltage V1 with the wire break detection threshold voltage Vth2 and outputs the comparison result to the microcontroller. In this case, the water leak detection comparator, the wire break detection comparator, and the microcontroller are collectively referred to as the control unit 21.

[0040] In the embodiment described above, an example was assumed in which a linear leak sensor is used for the leak sensor 10, but the leak sensor 10 is not limited to a linear leak sensor. Any type of leak sensor is acceptable as long as it is of a type in which the insulation resistance between the first electrode 11 and the second electrode 12 decreases when a conductive liquid enters between the first electrode 11 and the second electrode 12.

[0041] The embodiments may be specified by the following items.

[0042] [Item 1] A water leak sensor (10) having a first electrode (11) that conducts to a first fixed potential and a second electrode (12) that conducts to a second fixed potential, wherein the insulation resistance (Rs) between the first electrode (11) and the second electrode (12) decreases when a conductive liquid enters between the first electrode (11) and the second electrode (12), a first resistor (R1) connected between the first electrode (11) and the first fixed potential, a switch (S1) connected in series with the first resistor (R1) between the first electrode (11) and the first fixed potential of the water leak sensor (10), and a control unit (21) that detects the voltage of the first electrode (11) of the water leak sensor (10), and determines that there is a water leak if the detected voltage of the first electrode (11) is located on the second fixed potential side of the water leak detection threshold voltage, The control unit (21) intermittently operates the switch (S1), and if the voltage of the first electrode (11) is located on the second fixed potential side of the water leak detection threshold voltage during the ON period of the switch (S1), the ON period of the switch (S1) is extended for a predetermined time, and if the voltage of the first electrode (11) remains on the second fixed potential side of the water leak detection threshold voltage for the extended period, the water leak detection circuit (20) confirms the determination of the water leak. This makes it possible to determine the presence or absence of a water leak with high accuracy while suppressing the deterioration of the water leak sensor (10). [Item 2] A water leak detection circuit (20) according to Item 1, wherein the first electrode (11) and the second electrode (12) are connected by a second resistor (R2), and the control unit (21) determines that at least one of the first electrode (11) or the second electrode (12) is disconnected when the voltage of the first electrode (11) is located on the first fixed potential side of the disconnection detection threshold voltage, which is set on the first fixed potential side of the water leak detection threshold voltage. With this, a dry state and a disconnection can be clearly distinguished by simply monitoring the voltage of the first electrode (11).[Item 3] The leak detection circuit (20) described in Item 1, wherein the first fixed potential is a high-side reference potential, the second fixed potential is a low-side reference potential, the switch (S1) is a P-channel semiconductor switch (S1), the control unit (21) detects the voltage of the first electrode (11) of the leak sensor (10), and determines that there is a leak if the detected voltage of the first electrode (11) is lower than the leak detection threshold voltage, and the control unit (21) intermittently operates the P-channel semiconductor switch (S1), and if the voltage of the first electrode (11) is lower than the leak detection threshold voltage during the ON period of the P-channel semiconductor switch (S1), the ON period of the P-channel semiconductor switch (S1) is extended for a predetermined time, and if the voltage of the first electrode (11) remains lower than the leak detection threshold voltage for the extended period, the leak determination is confirmed. [Item 4] The leak detection circuit (20) described in Item 1, wherein the first fixed potential is a low-side reference potential, the second fixed potential is a high-side reference potential, the switch (S1) is an N-channel semiconductor switch (S1), the control unit (21) detects the voltage of the first electrode (11) of the leak sensor (10), and determines that there is a leak if the detected voltage of the first electrode (11) is higher than the leak detection threshold voltage, and the control unit (21) intermittently operates the N-channel semiconductor switch (S1), and if the voltage of the first electrode (11) is higher than the leak detection threshold voltage during the ON period of the N-channel semiconductor switch (S1), the ON period of the N-channel semiconductor switch (S1) is extended for a predetermined time, and if the voltage of the first electrode (11) remains higher than the leak detection threshold voltage for the extended period, the leak determination is confirmed.[Item 5] A water leak detection system (1) comprising: a water leak sensor (10) having a first electrode (11) that conducts to a first fixed potential and a second electrode (12) that conducts to a second fixed potential, wherein the insulation resistance (Rs) between the first electrode (11) and the second electrode (12) decreases when a conductive liquid enters between the first electrode (11) and the second electrode (12); a second resistor (R2) connected between the first electrode (11) and the second electrode (12) and connected between the first electrode (11) of the water leak sensor (10) and the first fixed potential; and a water leak detection circuit (20) described in any one of items 1 to 4. With this, it is possible to determine the presence or absence of a water leak with high accuracy while suppressing deterioration of the water leak sensor (10).

[0043] This disclosure can be used for water leak detection using a water leak sensor.

[0044] 1 Leak detection system, 10 Leak sensor, 11 First electrode, 12 Second electrode, 13a First internal braid, 13b Second internal braid, 13c External braid, 20 Leak detection circuit, 21 Control unit, R1 First resistor, R2 Second resistor, Rs Insulation resistor, S1 Switch, CN1 Connector.

Claims

1. A water leak detection circuit comprising: a first electrode of a water leak sensor having a first electrode that conducts to a first fixed potential and a second electrode that conducts to a second fixed potential, wherein the insulation resistance between the first electrode and the second electrode decreases when a conductive liquid enters between the first electrode and the second electrode; a first resistor connected between the first electrode of the water leak sensor and the first fixed potential; a switch connected in series with the first resistor between the first electrode of the water leak sensor and the first fixed potential; and a control unit that detects the voltage of the first electrode of the water leak sensor and determines that there is a water leak if the detected voltage of the first electrode is located on the second fixed potential side of the water leak detection threshold voltage, wherein the control unit intermittently operates the switch, and if the voltage of the first electrode is located on the second fixed potential side of the water leak detection threshold voltage during the switch's ON period, the ON period of the switch is extended for a predetermined time, and if the voltage of the first electrode remains on the second fixed potential side of the water leak detection threshold voltage for the extended period, the determination of a water leak is confirmed.

2. The water leak detection circuit according to claim 1, wherein the first electrode and the second electrode are connected by a second resistor, and the control unit determines that at least one of the first electrode or the second electrode is disconnected when the voltage of the first electrode is located on the first fixed potential side of the disconnection detection threshold voltage, which is set to be on the first fixed potential side of the water leak detection threshold voltage.

3. The leak detection circuit according to claim 1, wherein the first fixed potential is a high-side reference potential, the second fixed potential is a low-side reference potential, the switch is a P-channel semiconductor switch, the control unit detects the voltage of the first electrode of the leak sensor, determines that there is a leak if the detected voltage of the first electrode is lower than the leak detection threshold voltage, and the control unit intermittently operates the P-channel semiconductor switch, and if the voltage of the first electrode is lower than the leak detection threshold voltage during the ON period of the P-channel semiconductor switch, extends the ON period of the P-channel semiconductor switch for a predetermined time, and if the voltage of the first electrode remains lower than the leak detection threshold voltage for the extended period, confirms the determination of a leak.

4. The leak detection circuit according to claim 1, wherein the first fixed potential is a low-side reference potential, the second fixed potential is a high-side reference potential, the switch is an N-channel semiconductor switch, the control unit detects the voltage of the first electrode of the leak sensor, determines that there is a leak if the detected voltage of the first electrode is higher than the leak detection threshold voltage, and the control unit intermittently operates the N-channel semiconductor switch, and if the voltage of the first electrode is higher than the leak detection threshold voltage during the ON period of the N-channel semiconductor switch, extends the ON period of the N-channel semiconductor switch for a predetermined time, and if the voltage of the first electrode remains higher than the leak detection threshold voltage for the extended period, confirms the determination of a leak.

5. A water leak detection system comprising: a water leak sensor having a first electrode that conducts to a first fixed potential and a second electrode that conducts to a second fixed potential, wherein the insulation resistance between the first electrode and the second electrode decreases when a conductive liquid enters between the first electrode and the second electrode; a second resistor connected between the first electrode and the second electrode and connected between the first electrode of the water leak sensor and the first fixed potential; and a water leak detection circuit according to any one of claims 1 to 4.

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