Leak detection

Abstract

A method of detecting the presence of a liquid is described, the method comprising: receiving a plurality of signals, each signal indicating a corresponding impedance across a respective sensing circuit of a plurality of sensing circuits, each sensing circuit configured such that the corresponding impedance across the sensing circuit decreases when the sensing circuit is exposed to the liquid; determining, for each sensing circuit of the plurality of sensing circuits, whether an impedance across the sensing circuit is below a threshold impedance; and, in response to determining that the impedance of each sensing circuit in the set of the plurality of sensing circuits is below the threshold impedance, outputting an indication of the presence of the liquid.

Description

Technical Field

[0001] The present application relates to systems and methods for detecting liquids, such as leak detection. Background Art

[0002] Various leak sensors operate by detecting a short circuit when any part of the sensor element becomes wet. For example, a conductive rope sensor consists of a long, thin rope containing a conductive element. When part of the rope becomes wet, a short circuit is created, completing the circuit until the rope dries out.

[0003] However, the sensitivity of such sensors is often not appropriate for the desired situation, for example because expected small amounts of water trigger false positive events in the sensor, or because they are not sensitive enough to alert of a leak event early enough in the process to mitigate the damage. Summary of the Invention

[0004] According to one aspect of the present invention, a method for detecting liquid is provided, the method comprising: receiving a plurality of signals, each signal indicating a corresponding impedance across a corresponding sensing circuit in a plurality of sensing circuits; each sensing circuit being configured such that the corresponding impedance across the sensing circuit changes when the sensing circuit is exposed to liquid; for each sensing circuit in the plurality of sensing circuits, determining whether the impedance across the sensing circuit is within a predefined range of impedances (e.g., an impedance range); and outputting an indication of liquid in response to determining that the impedances of the set of the plurality of sensing circuits are each within the predefined range of impedances.

[0005] In use, the impedance across each sensing circuit may depend on the amount of water or other liquid to which the sensing circuit is exposed (e.g., located on or near the sensing circuit). For example, exposing a sensing circuit to a greater amount of water or other liquid may reduce the impedance across the sensing circuit. Thus, an impedance across a sensing circuit below a threshold impedance may indicate that water or another liquid is present on the sensing circuit, or an impedance across a sensing circuit above a threshold impedance may indicate that the sensing circuit is dry. The impedance of a sensing circuit may be affected by liquid conducting across (short-circuited) portions of the sensing circuit (such as a track), or by a reduction in capacitance between such portions of the sensing circuit (e.g., when the sensing circuits are close together).

[0006] Alternatively, another type of liquid (e.g., a non-conductive liquid) may cause the impedance to decrease. In this case, the presence of such a liquid can be detected by an increase in impedance or by the impedance across the sensing circuit being above a threshold impedance. Depending on the specific use case, liquid can be detected based on the impedance crossing a threshold impedance. In one embodiment, this involves detecting whether the impedance is above a threshold impedance. In an alternative embodiment, this involves detecting whether the impedance is below a threshold impedance. Therefore, whether the impedance across the sensing circuit is above or below the threshold can be used to determine whether water is located on or near these sensing circuits.

[0007] In some embodiments, the predefined range of impedance may be an impedance range below a threshold impedance (e.g., a range from a threshold impedance to zero impedance). In alternative embodiments, the predefined range of impedance may be an impedance range above a threshold impedance (e.g., a range from a threshold impedance to infinite impedance).

[0008] Existing water sensors that output a leak indication when the impedance across only a single sensing circuit drops, such as conductive rope sensors, are prone to oversensitivity and produce false positive leak indications. Determining a collection of multiple sensing circuits, each with an impedance below a threshold impedance, allows for improved leak detection accuracy.

[0009] In some embodiments, the liquid indication may be an indication of the presence of liquid outputted in response to determining that the set includes at least a threshold number of sensing circuits. In such embodiments, the method may include outputting an indication of the absence of liquid in response to the set including less than the threshold number of sensing circuits.

[0010] A higher threshold number results in a lower sensitivity of the sensor and a lower likelihood of false positive detections (the system is more robust to false positives). Avoiding such false positives in this manner can advantageously prevent the use of time, money, equipment, or consumables in unnecessary response to less severe leaks, and can avoid fatigue or loss of confidence in the leak detector, thereby improving crew readiness and response time to actual severe leak events.

[0011] Each of the plurality of sensing circuits may include a pair of conductive tracks separated by a corresponding gap. The conductive tracks may be located on a substrate. In use, the gap between the conductive tracks may be partially or fully bridged by water or another conductive fluid, thereby reducing the impedance between the two tracks and / or across the circuit, or the gap between the two tracks may be completely short-circuited, significantly reducing the impedance across the circuit. Each track of the sensing circuit may include an electrode for connection to a leak detector. The impedance across the sensing circuit including the pair of electrodes may be measured between the electrodes included in the pair of tracks.

[0012] In some embodiments, the method can be performed by a liquid sensor (such as a leak sensor) or its processor. The sensor or a system including the sensor can include multiple sensing circuits. Each sensing circuit can be connected to the same device or sensor. The method can be implemented by a computer.

[0013] The two electrodes of each sensing circuit can be connected to different voltages, for example, via one or more of a bias circuit system, a generalized impedance, a resistor, a current source, a current sink, and a voltage divider (any of which can form part of a sensor). In some embodiments, one of the two conductive tracks of each sensing circuit can be connected directly to a ground voltage, or connected to a ground voltage via one or more of a bias circuit system, a generalized impedance, a resistor, a current source, a current sink, and a voltage divider. The other of the two conductive tracks can be connected to a voltage source or voltage line via one or more of a bias circuit system, a generalized impedance, a resistor, a current source, a current sink, and a voltage divider. In some embodiments, each electrode can be connected to its corresponding voltage (or, when measuring the impedance between the electrode and another electrode, the electrode can be controlled to do so) with equal impedance, substantially equal impedance, or impedance of the same magnitude. When measuring impedance between electrodes, the impedance of each electrode (and therefore each track connected thereto) to its corresponding voltage is more similar, which may cause the common mode noise experienced by the two tracks to be similar in amplitude and phase, thereby reducing the impact of noise on the measurement.

[0014] In some embodiments, one or more conductive tracks and / or electrodes connected thereto can be shared between multiple sensing circuits. For example, in some embodiments, each sensing circuit may include a corresponding track and / or electrode that forms only a portion of the sensing circuit, and a common conductive track and / or electrode shared between one or more other sensing circuits (e.g., between all other sensing circuits). The common conductive track and / or electrode can be directly connected to ground, or can be connected to ground via one or more of the bias circuitry, generalized impedance, resistor, current source, current sink, and voltage divider as described above. The common conductive track and / or electrode may experience common-mode noise that is substantially similar in phase and amplitude to the individual tracks and / or electrodes. Therefore, measuring the impedance or voltage difference between the common track and / or electrode and the individual tracks and / or electrodes can reduce the noise within the measurement.

[0015] The tracks forming part of each sensing circuit may be substantially parallel to one another, or may include multiple segments that are parallel to corresponding segments of (one or more) other tracks. The tracks of each sensing circuit may include multiple interdigitated segments. This arrangement may enable the sensing circuits to cover a relatively large area. The spacing between the two tracks of each sensing circuit may be substantially constant along the length of the tracks and / or substantially constant relative to the spacing between the tracks of other sensing circuits.

[0016] The impedance between two conductive tracks of the sensing circuit can be determined by measuring the voltage of each conductive track.

[0017] The plurality of sensing circuits may include three or more sensing circuits, four or more sensing circuits, may include eight or more sensing circuits, or may include twelve or more sensing circuits.

[0018] In some embodiments, the multiple circuits can be located in different parts of the substrate and / or can extend over different parts of the substrate. This can make it possible to detect the location of a leak in the area spanned by the substrate. In some embodiments, the substrate on which the conductive tracks of the multiple sensing circuits are located can be an elongated strip. The multiple sensing circuits can be located at different points along the length of the elongated strip and / or can span different lengths along the length of the elongated strip. This can allow the leak to be located along the length of the strip.

[0019] The substrate can be substantially planar, thereby allowing it to be placed on a surface and / or within narrow gaps between structures or systems, and allowing the volume of space occupied by the system to be reduced. The substrate can be made of an impermeable material, such as a plastic material. For example, the substrate can be a polyethylene terephthalate (PET) substrate. The substrate can be made of a flexible material so that it can conform to a surface during use.

[0020] In some embodiments, each conductive track is printed on the substrate, for example, using conductive ink. The conductive ink can be an ink that is robust (e.g., chemically inert, physically stable, insoluble, etc.) in (e.g., in contact with) a specific target liquid or a collection of target liquids to help detect these specific targets. For example, the target liquid can be water or an aqueous solution. For example, the conductive ink can be a carbon-based ink. Unlike metal-based inks, carbon-based inks do not form ions when in contact with water, which could cause the ink to react and possibly creep, potentially leading to false positive or false negative results. Each sensing circuit can span a different portion of the substrate. The substrate can be an elongated strip, and each sensing circuit can span a different portion of the length of the substrate.

[0021] In some embodiments, each conductive track is connected to a corresponding voltage through a circuit having a corresponding impedance, wherein the corresponding impedances are substantially equal to one another.

[0022] In some further embodiments, each conductive track is connected to a corresponding voltage via a variable impedance circuit having a variable impedance, and the method further comprises determining, for each conductive track, a corresponding impedance of the conductive track and configuring the corresponding variable impedance circuit to have the determined impedance. The impedance of a given conductive track can be determined based on configuration data stored in a memory of the liquid sensor. The impedance of each conductive track can be determined by determining the type of each sensing circuit, and for each sensing circuit, determining the impedance of each conductive track based on configuration data that stores an association between the conductive track and the impedance for each type of sensing circuit. The type of sensing circuit can be determined by sensing an electrical characteristic of the sensing circuit.

[0023] In some embodiments, the substrate may include an adhesive element, such as an adhesive surface or backing, which may be used to position the substrate in a desired location. For example, the substrate may be adhered to a fluid-carrying pipe so that it extends along the length of the pipe to detect any leaks from the pipe.

[0024] The substrate can be configured to be releasably connected to a sensor performing the method and / or electrodes included in the sensor. This can allow the substrate and sensing circuit to be replaced (for example, when they are damaged), or to provide a sensor with a different arrangement or a different number of sensing circuits.

[0025] In some embodiments, the method may further include detecting when one or more sensing circuits are damaged due to damage, for example, as a result of a crack or tear in the substrate, as described above. Such damage may be detected when the impedance across the sensing circuit exceeds a breakage threshold, which is higher than the impedance threshold as described above and may correspond to a significant increase in impedance when the circuit is physically broken. Alternatively or additionally, damage may be detected when the impedance across a breakage circuit (which may include an uninterrupted conductive loop extending across or around the substrate, such as around the periphery of the substrate) decreases or falls below a breakage circuit threshold impedance. The substrate may include one or more such breakage circuits. Upon detection of damage, an indication of such damage may be output.

[0026] The method includes determining whether the impedance across each sensing circuit is within a predetermined range of impedances (such as below a threshold impedance), and outputting an indication of liquid in response to determining that the impedances of the set of multiple sensing circuits are each within the predetermined range.

[0027] As described above, water or another liquid on or near a sensing circuit can reduce the impedance across the sensing circuit. Thus, an impedance across the sensing circuit below or above a threshold impedance can indicate that the amount of water on or near the sensing circuit is greater than or less than a threshold, respectively. Thus, the dryness or wetness of the sensing circuit can be determined, and an indication can be output based on this determination.

[0028] Thus, the method can be used to detect the undesirable presence of liquid when the impedance of a set of sensing circuits is below a threshold impedance, for example, to detect a leak. However, in some cases, if only a relatively small amount of water condenses, falls, or splashes onto a sensing circuit—such as, as described above, onto a sensing circuit defined by a track on a substrate—then leak detection may not be desired. Thus, the indication can be an indication of the presence of liquid, which is output only when a set of sensing circuits, each of which has an impedance across the sensing circuit determined to be below a threshold impedance, meets certain criteria, for example, if the set includes at least a threshold number of sensing circuits having an impedance across the sensing circuit below an impedance threshold (e.g., where the threshold number is two or more). In such an embodiment, determining whether the impedance across each sensing circuit is within a predetermined range can include, for each sensing circuit, determining whether the impedance across the sensing circuit is below the threshold impedance.

[0029] Alternatively or additionally, in response to a set of sensing circuits where the impedance across each sensing circuit is determined to be above a threshold impedance (which may be the same or different than the threshold impedance for indicating the presence of liquid as described above), meeting certain criteria, for example, if the set includes at least a threshold number of sensing circuits (which may also be the same or different than the threshold number for indicating the presence of liquid as described above), an indication of the absence of liquid may be output. In such embodiments, these threshold impedances and / or threshold number of sensing circuits may include any of the features outlined below with respect to the threshold impedances and / or threshold number of sensing circuits for indicating the presence of liquid.

[0030] The threshold number of sensing circuits and / or threshold impedance can be modified and / or selected, for example, depending on the method and / or situation in which the sensor is being employed. For example, a sensor located on a surface below a hot water heater that is expected to be dry and free of condensation or other sources of false positives can be configured with a lower threshold number of circuits than a sensor located outside near an exterior door where condensation or splashing is expected.

[0031] In some embodiments, the threshold amount may be adjusted based on user input.

[0032] In some embodiments, the threshold number of sensing circuits may be one, or may be selected from one to any number between the number of sensing circuits connected to or included in the sensor. In other embodiments, the threshold number of sensing circuits may be only two or more, or may be selected to be only two or more, or may vary between two or more.

[0033] In some embodiments, the threshold number can depend on previous detections, previous output indications, and / or the state of the system. After outputting an indication of the presence of liquid and / or after determining that the set of sensing circuits includes at least a threshold number of sensing circuits, the threshold number can be reduced. After outputting such an indication and / or making such a determination, a transition can be made to a "wet" state, within which a lower threshold number can be used. This can ensure that a sufficient number of sensing circuits have dried before determining that water is no longer present, and / or can prevent small fluctuations in the number of wet circuits, such as noise fluctuations, from causing rapid transitions into and out of the wet state. Similarly, the threshold number can be increased after outputting an indication of the absence of liquid and / or after determining that the set of sensing circuits includes fewer than a threshold number of sensing circuits, for example, upon entering a "dry" state. Alternatively, the threshold number can be increased after outputting an indication of the presence of liquid, after determining that the set of sensing circuits includes at least a threshold number of sensing circuits, and / or within the wet state, and / or decreased within the dry state. That is, each time the number of sensing circuits in the set crosses a boundary between two ranges (e.g., a threshold number), the boundary can move in the opposite direction (e.g., increasing when the number of sensing circuits falls below the threshold number, or decreasing when the number of sensing circuits is greater than or equal to the threshold number). This avoids the system from repeatedly switching between ranges when the number of sensing circuits in the set oscillates around the boundary.

[0034] The impedance threshold value compared to the impedance across each sensing circuit can be the same. Alternatively, the impedance threshold value compared to the impedance across each sensing circuit can depend on the identity of the sensing circuit. In such an embodiment, different impedance threshold values ​​can be used for different sensing circuits.

[0035] In some embodiments, when determining whether the impedance across each of a plurality of sensing circuits is below or above a threshold impedance, the threshold impedance for all or an individual sensing circuit can be derived from current and / or historical values ​​of the impedance across one, some, or all of the sensing circuits. For example, the impedance threshold for an individual sensing circuit can be derived from current and / or historical values ​​of the impedance across the sensing circuit and / or across adjacent sensing circuits. This impedance value may be derived outside the fluctuation range of the impedance across the sensing circuit, for example, due to noise. In some embodiments, for each of the plurality of sensing circuits, the predefined range of impedances to which the impedance across the sensing circuit is compared is an impedance range below the corresponding threshold impedance, and upon determining that the impedance across the sensing circuit is below the corresponding threshold impedance, the corresponding threshold impedance is increased. In some embodiments, for each of the plurality of sensing circuits, the predefined range of impedances to which the impedance across the sensing circuit is compared is an impedance range greater than or equal to the corresponding threshold impedance, and upon determining that the impedance across the sensing circuit is greater than or equal to the corresponding threshold impedance, the corresponding threshold impedance is decreased. That is, each time the impedance of a given sensing circuit crosses the boundary between two impedance ranges, the boundary can be moved in the opposite direction (e.g., increasing when the impedance drops below a threshold impedance, or decreasing when the impedance becomes greater than or equal to the threshold impedance). This avoids the system from repeatedly switching between ranges as the impedance oscillates around the boundary.

[0036] In some embodiments, the threshold impedance can depend on previous detections, previous output indications, and / or the state of the system. After outputting an indication of the presence of liquid and / or determining that the set of sensing circuits includes at least a threshold number of sensing circuits, the threshold impedance can be lowered. After outputting such an indication and / or making such a determination, a transition to a "wet" state can be made, within which a lower impedance threshold can be used. This can ensure that the sensing circuits have been significantly dried before determining that water is no longer present, and / or can prevent small fluctuations in impedance, such as noise fluctuations, from causing rapid transitions to and exiting the wet state. Similarly, after outputting an indication of the absence of liquid and / or determining that the set of sensing circuits includes fewer than a threshold number of sensing circuits, the threshold impedance can be increased, for example, upon entering a "dry" state. Alternatively, the threshold impedance can be increased after outputting an indication of the presence of liquid, after determining that the set of sensing circuits includes at least a threshold number of sensing circuits, and / or within the wet state, and / or the threshold impedance can be decreased within the dry state.

[0037] In some embodiments, the indication of the liquid threshold is an indication of the presence of liquid outputted in response to determining that the set includes at least a threshold number of adjacent sensing circuits having an impedance below a threshold impedance. In such embodiments, the method may include outputting an indication of the absence of liquid in response to the set including fewer than the threshold number of adjacent sensing circuits.

[0038] The threshold number of adjacent circuits may include any of the optional features of the threshold number of circuits described herein.

[0039] The method may include detecting the number of sensing circuits across which the impedance is below a threshold impedance (i.e., the number of sensing circuits within a set). In such an embodiment, the indication of the liquid and / or other indications that may be output may indicate the severity of the leak and / or the number of sensing circuits across which the impedance is below the threshold impedance. Such an indication may specify the exact number of sensing circuits below the threshold impedance and / or may correspond to a range of numbers of sensing circuits below the threshold impedance. Such an indication may advantageously allow a user or device receiving the indication to determine the severity of the leak. For example, knowing the severity of the leak may enable facility managers to determine whether the leak requires immediate attention or is an emergency, thereby allowing them to efficiently allocate their limited resources.

[0040] In some embodiments, the number of sensing circuits in a set can be evaluated to determine whether it is within a plurality of different ranges, and in response to determining that the number of sensing circuits in the set is within one of the ranges, an indication can be output indicating which range the number of sensing circuits in the set is within. The indicated ranges can provide information to a user or system receiving the indication regarding the amount of liquid to which the sensing circuits were exposed, and thereby provide information regarding the severity of a leak detected by the sensor. The lowest of these ranges, or a number below any of the ranges, can indicate that the sensing circuits were not exposed to any liquid. The boundaries of these ranges can include any of the optional features described herein regarding the threshold number of circuits.

[0041] In some embodiments, the indication of liquid is an indication of the presence of liquid output in response to determining that the number of sensing circuits in the set whose impedance is below a threshold impedance is within one of a plurality of ranges, and the indication of the presence of liquid indicates the range within which the number of sensing circuits in the set falls. In such embodiments, the method may include outputting an indication of the absence of liquid in response to the set including a lower limit that is less than a lower limit of a lower range in the plurality of ranges. The plurality of ranges may include three or more ranges.

[0042] In some embodiments, a plurality of states can be transitioned between, each corresponding to a different number of sensing circuits across which the impedance is below a threshold impedance (i.e., corresponding to a different number of sensing circuits within the set). The number of states can be one greater than the number of sensing circuits, for example, such that there is a corresponding state for each possible number of sensing circuits below the impedance threshold, including a state in which no sensing circuits are below the impedance threshold. Alternatively, each state can correspond to a range of numbers of sensing circuits below the impedance threshold. In some embodiments, an indication can be output upon transitioning between states.

[0043] While within a given state, the number of sensing circuits across which the impedance is below an impedance threshold can be evaluated. After evaluating the number of circuits below the impedance threshold, it can be determined whether the number of sensing circuits below the impedance threshold corresponds to a different state, and if so, a transition can be made to that state. In other embodiments, after evaluating the number of circuits below the impedance threshold, it can be determined whether the number of sensing circuits below the impedance threshold is above a value for transitioning to a sequentially more severe state (a state corresponding to a greater number of sensing circuits below the impedance threshold), and / or it can be determined whether the number of sensing circuits below the impedance threshold is below a value for transitioning to a sequentially less severe state (a state corresponding to a lesser number of sensing circuits below the impedance threshold). In some such embodiments, the value for transitioning from a first less severe state to a second more severe state may be lower than the value for transitioning from the second more severe state to the first less severe state.

[0044] In some embodiments, as described above, the impedance threshold and / or the number of sensing circuits used to transition between states can depend on the state the system is currently in. In response to determining that the number of sensing circuits in the set is within one of the multiple ranges, the one of the multiple ranges can be expanded, for example, by reducing the threshold number of sensing circuits at the boundary between the range and the range corresponding to the smaller number of sensing circuits. Alternatively, the threshold number can be increased. Alternatively or additionally, the threshold number of sensing circuits at the boundary between the range and the range corresponding to the larger number of sensing circuits can be increased or decreased.

[0045] In some embodiments, the impedance across each of the plurality of sensing circuits can be compared to a threshold impedance, and / or the number of sensing circuits below the impedance threshold can be determined periodically (e.g., once per minute). Evaluating the impedance and / or the number of circuits below the impedance threshold less frequently can reduce power consumption of the sensor. In some embodiments, the number of sensing circuits below the impedance threshold can be re-evaluated immediately or shortly after transitioning from one state to another, and the number of sensing circuits below the impedance threshold can be re-evaluated after a set period of time after evaluating the number of sensing circuits below the impedance threshold and determining that no state transition is necessary.

[0046] In some embodiments, in addition to detecting the number of sensing circuits across which the impedance is below the threshold impedance (i.e., the number of sensing circuits within the set), the method may also include detecting which sensing circuits of the plurality of sensing circuits have an impedance across which the impedance exceeds the threshold impedance (i.e., the identity of the sensing circuits within the set). Identification of the liquid may indicate the identity or location of one or more sensing circuits within the set.

[0047] In some embodiments, the threshold number of sensing circuits, range of number of sensing circuits, and / or value for transitioning between states as described above may be, or may be capable of being, set to a number of adjacent and / or consecutive sensing circuits, such as three or more adjacent and / or consecutive sensing circuits. This may prevent multiple sensing circuits simultaneously experiencing splashing or condensation at different points across the substrate from triggering an indication of liquid presence, while allowing leaks on multiple adjacent sensing circuits to trigger such an indication.

[0048] In some embodiments, the method may include, for each of a plurality of preset combinations of sensing circuits, determining whether an impedance across each sensing circuit in the preset combination is below a threshold impedance, wherein an indication of liquid presence and / or another output indication indicates the identity and / or location of each preset combination for which the impedance across each sensing circuit in the preset combination is below the threshold impedance, and / or whether the impedance of a particular combination of sensing circuits is below the threshold impedance.

[0049] Some embodiments may include evaluating whether the impedance across all sensing circuits in one or more preset combinations is below an impedance threshold. If the impedance across all sensing circuits in a given preset combination is below the impedance threshold, an indication of the identity of that combination (such as an index value) may be added to a field. After evaluating all combinations, an indication may be output that includes or is derived from the field. Some or all preset combinations may include multiple sensing circuits. Some or all preset combinations may include only a single sensing circuit.

[0050] In some embodiments, the sensor may output an indication of liquid presence only if the impedance across the sensing circuits meets the requirements for outputting the above indication for more than a threshold period of time (and / or for more than a threshold number of repeated measurements). For example, the sensor may output an indication of liquid presence only if the impedance across at least a threshold number of sensing circuits is below an impedance threshold for more than a threshold period of time. This can avoid outputting an indication based solely on short-term impedance changes.

[0051] Each output indication (such as an indication of the presence of liquid) can be or include an electronic signal, such as a wireless electronic signal. The wireless electronic signal can be transmitted based on Long Range Wide Area Network (LoRaWAN), Bluetooth, Wi-Fi, Global System for Mobile Communications (GSM), Long Term Evolution (LTE), and / or Narrowband Internet of Things (NB-IoT) radio technology. The electronic signal indication can be sent to a separate system, such as a controller or a central monitoring system, for example, a controller of a building in which the leak sensor is located. Alternatively or additionally, the electronic signal indication can be transmitted to a cloud computing system or platform.

[0052] Alternatively or additionally, each indication may be or include a signal to a user, such as a visual indication, which may be output by a display and / or one or more other light-emitting components (such as LEDs) that may be included in the leak sensor performing the method. Alternatively or additionally, the indication may include and / or be an audible signal that may be output by a speaker included in the leak sensor performing the method.

[0053] In some embodiments, an output indication (such as an indication of the presence of liquid) may be output continuously or repeatedly until the condition triggering its output is no longer met, for a set period of time, until a circumstance triggers an update of the indication (such as an increase in the number of sensing circuits below an impedance threshold specified in the indication), and / or until a cancel or reset instruction is received.

[0054] For example, after an indication is triggered to be transmitted, the sensor may enter a triggered state in which the indication is continuously or intermittently output until the sensor is reset. Continuing to output the indication even if the condition that triggered it is no longer met ensures that the user or controller is notified that a leak has occurred even if the leak subsequently dries up.

[0055] It will be appreciated that for each of the above-described embodiments in which an indication of the presence of liquid is output in response to a collection of multiple sensing circuits whose impedance is below a threshold impedance satisfying some criteria, in another embodiment, an indication of the absence of liquid may be output in response to a collection of multiple sensing circuits whose impedance is above a threshold impedance satisfying the same criteria.

[0056] According to a second aspect of the invention, a sensor is provided, which is configured to: receive a plurality of signals, each signal indicating a corresponding impedance across a corresponding sensing circuit in a plurality of sensing circuits, each sensing circuit being configured such that the corresponding impedance across the sensing circuit changes when the sensing circuit is exposed to liquid; for each sensing circuit in the plurality of sensing circuits, compare the impedance across the sensing circuit with a threshold impedance; and in response to determining that the impedance of the set of the plurality of sensing circuits is each lower than or each higher than the threshold impedance, output an indication of the presence of liquid.

[0057] The leak sensor may be configured to perform any optional features of the above methods and / or may include any optional features of the above sensors.For example, the leak sensor may include one or more sensing circuits.

[0058] The leak sensor may include: a processor that can be configured to perform the steps described herein; a memory that can store computer instructions that, when executed by the processor, cause the processor to perform the steps described herein; a housing; one or more electrodes for connecting to a sensing circuit or its tracks as described above; a power source, such as a battery; a communication device, such as a wireless interface, for outputting indications as described herein; and / or other indicators for outputting indications as described herein to a user, such as a display, a speaker, one or more lights, or other suitable devices.

[0059] According to a third aspect of the present invention, one or more storage media are provided, wherein the one or more storage media store computer-executable instructions, which, when executed by a processor, cause the method according to the first aspect to be performed. The storage medium may be non-transitory.

[0060] A more complete understanding and appreciation of the embodiments of the present invention will be provided through the following detailed description which is given by way of example only and in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a diagram of a first example of a leak detection system;

[0062] Figure 2 A second example of a leak detection system is shown;

[0063] Figure 3a Shown Figure 2 A sensing circuit substrate for a leakage detection system;

[0064] Figure 3b An alternative sensing circuit substrate is shown;

[0065] Figure 4 It is a system diagram of the leak detection system;

[0066] Figure 5 is a flow chart of a method of operating a processor of a leak detection system;

[0067] Figure 6 is a flow chart of a classification algorithm in which a leakage sensor is classified into a state based on a number of its sensing circuits having an impedance across the sensing circuits below an impedance threshold; and

[0068] Figure 7 is a flow chart of a classification algorithm in which a leak sensor is classified into a certain state based on the location where the leak occurs on the sensing circuit. DETAILED DESCRIPTION

[0069] Referring generally to the figures, embodiments of a leak detection system are shown that includes a plurality of sensing circuits and a processor configured to output an indication of the presence of liquid based on impedance across the sensing circuits. Such a leak detection system can advantageously provide a device for detecting leaks with adjustable sensitivity, can classify leaks of different types or severities, and / or can enable the location of a leak to be determined.

[0070] Figure 1 A diagram shows an example of a leak detection system 100 that includes a leak sensor 110 and a plurality of sensing circuits 120. The leak sensor 110 is configured to measure impedance across each of the plurality of sensing circuits 120 and, in response to determining that the impedance across a group of sensing circuits 120 is below a threshold impedance, output an indication via an output 150.

[0071] The illustrated example system 100 includes three sensing circuits 120a, 120b, and 120c. However, it will be appreciated that the system 100 may include other numbers of sensing circuits 120. These sensing circuits 120 are spatially separated to detect the presence of water or other conductive fluids at different locations covered by the leak detection system 100.

[0072] Each of the sensing circuits 120 comprises two conductive tracks 130 , 140 at different voltages, separated by a gap which provides an impedance between them. In the example system 100 , the two conductive tracks are a positive track 130 and a ground track 140 .

[0073] Each of the ground rails 140 is connected to a ground voltage source 142 provided by the leakage sensor 110 via a corresponding switch 148, a corresponding impedance 144 (e.g., a circuit with a specific impedance, such as a resistor), and a corresponding ground electrode 146. The ground electrode 146 of each positive rail electrically connects the rail to the leakage sensor 100. Each of the positive rails 130 is connected to a positive voltage source 132 provided by the leakage sensor 110 via a shared impedance 134 and a shared positive electrode 132. The shared ground electrode connects all of the positive rails 130 to the leakage sensor 100. After the ground rail 140 of each sensing circuit 120 is connected to the ground voltage source 142 via its corresponding switch 148 and allowed to stabilize for a dwell time, the impedance across the sensing circuit can be measured between electrodes 136 and 146 at the location where the rails 130 and 140 of that sensing circuit are connected to the leakage sensor 100. When making measurements, the other ground rails 140 are disconnected from the ground voltage source 142 via their corresponding switches 148. This ensures that the voltage measured is only on the selected electrodes.

[0074] like Figure 1As shown in , the two tracks 130, 140 of each sensing circuit can include multiple interdigitated fingers, allowing the sensing circuit to cover a wider area. The interdigitated fingers can have substantially equal spacing to provide consistent sensitivity throughout the sensing circuit.

[0075] As a result of this arrangement, the positive rail 130 and ground rail 140 of each sensing circuit 120 are biased at different voltages, with the impedance between them provided by the gap. When water or another conductive fluid falls onto the sensing circuit 120, it partially or completely crosses the gap, thereby reducing the impedance between the two rails 130 and 140. Therefore, when the impedance across the sensing circuit 120 is below an impedance threshold, the leak sensor 110 can determine that water or another conductive substance is present on the sensing circuit 120.

[0076] The impedance 144 between each ground rail 140 and the ground voltage source 142 can be equal to, substantially equal to, or of the same order of magnitude as, the impedance between the positive rail 130 and the positive voltage source 130, or can be configured or controlled to be so when measuring the impedance across the sensing circuit and / or when its corresponding switch 134, 144 is closed. During measurement, the impedance of each rail 130, 140 to its corresponding source 132, 142 is more similar, which can cause the common-mode noise experienced by the two rails 130, 140 to be similar in amplitude and phase, thereby reducing the impact of noise on the measurement.

[0077] In some examples, the impedances 134, 144 between the rails 130, 140 and their corresponding voltage sources 132, 142 can be provided by resistors. These resistors can have a fixed impedance that can be large enough to substantially dominate the impedance between the rails 130, 140 and their corresponding voltage sources 132, 142 (compared to negligible impedances of other components between the rails and the sources). In alternative embodiments, the impedances 134, 144 can be electronically variable, such as by a potentiometer (e.g., a digital potentiometer).

[0078] The impedances 134, 144 between the rails 130, 140 and their corresponding voltage sources 132, 142 can be set by component selection during the design and / or construction of the sensor 110. Alternatively, these impedances 134, 144 can be set by the sensor 110 at boot time. The sensor 110 can identify the sensing circuit 120 attached to it or its configuration and can set the impedance in response thereto. For example, the sensor 110 can be configured to read the impedance configuration corresponding to the sensing circuit 120 from a memory (e.g., a table stored in firmware) and then configure the variable impedance circuit (e.g., a digital potentiometer) to achieve that specific impedance between the rails 130, 140 and their corresponding voltage sources 132, 142.

[0079] When the threshold impedance across a certain number or combination of sensing circuits 120 is below the impedance threshold, the leak sensor 110 can determine that the impedance drop is not the result of a minor and / or isolated splash, condensation, or other environmental condition, but rather the result of a more serious leak. When such a detection occurs, the leak sensor 110 outputs an indication 150 that the presence of such liquid has been detected.

[0080] It will be appreciated that in alternative leak sensor systems 100, the two rails of some or all of the sensing circuitry may be connected to two different voltages, rather than to a positive voltage and ground; the impedance(s) between one of the voltages provided by the leak detector 110 (e.g., the positive voltage 132) and the corresponding electrode(s) may be omitted; and / or the two sets of rails 130, 140 may be connected via separate corresponding impedances and / or electrodes, rather than the shared impedance 134 and electrodes 136 shown above; and other suitable modifications.

[0081] Figure 2 A detailed view of an example leak sensor system 105 is shown, which includes the leak sensor system 105 described above with reference to FIG. Figure 1 All features of the described system 100 are shown. The sensor system 105 includes twelve sensing circuits 120, but only the first two 120a and 120b are shown in full.

[0082] The leak sensor 110 includes a housing 112 (e.g., a waterproof housing) that contains a power source (e.g., a battery), a processor, a memory storing computer instructions (which, when executed by the processor, cause it to perform the steps described herein), a LoRaWAN transceiver for outputting an indication 150; and electrodes 136, 146 for connecting to the tracks 130, 140 of the sensing circuit 120.

[0083] The sensing circuit 120 is provided on an elongated flexible substrate 125 (e.g., a polyethylene terephthalate (PET) substrate) and is defined by tracks 130, 140, 145 printed on the elongated flexible substrate using conductive ink. The tracks 130, 140, 145 are printed in multiple layers to allow the tracks to cross each other without being electrically connected to each other. The electrodes 136, 146 at which each track 130, 140, 145 connects to the leak sensor are provided on a tab at one end of the substrate 125, which, when in use, extends into the interior of the housing 112 of the leak sensor 110.

[0084] Each of the ground rails 140, 145 includes a first surface portion 140 defining a plurality of interdigitated fingers with a corresponding portion of the positive rail 130 over a limited portion of the substrate length, and a second subsurface portion 145 extending from the ground rail's electrode 146 to the first surface portion. The subsurface portion 145 of each track extends below the surface portion 140 of each conductive track, covering an area closer to the electrode than the track itself.

[0085] Substrate 125 includes a stack of layers consisting of: a base layer; a subsurface conductive layer, including a second subsurface portion 145 of the track located on the base layer; one or more insulating dielectric layers on the first conductive layer, insulating the second subsurface portion 145 from the first surface portion 140 at their intersection; and a final surface conductive carbon layer, including the first surface portion 140 of the track. The substrate may include multiple insulating dielectric layers between the two conductive layers to minimize the possibility of pinholes piercing the dielectric layers and providing an unwanted electrical connection between the first and second portions 140, 145 of the track. The portion of the subsurface conductive layer where the first and second subsurface portions 145 intersect with the first surface portion 140 of the surface conductive layer is uncovered by the dielectric layer, allowing the surface layer to be printed directly onto the subsurface portions 145 of the track. In other words, the insulating layer is configured to allow some tracks to cross without shorting the system. The sensing area (interdigitated fingers) is exposed, so that no insulating layer covers the track above the sensing area.

[0086] Figure 2 The portion of substrate 125 shown in FIG shows first portion 140 a and second portion 145 a of the first ground track of first sensing circuit 120 a, first portion 140 b and second portion 145 b of the second ground track of second sensing circuit 120 b, and some of the second portions of the third through twelfth ground tracks, including second portion 145 c of the third ground track of the third sensing circuit.

[0087] Figure 3a Shown Figure 2 FIG1 is an overall view of substrate 125 and sensing circuit 120 used in system 105. A subsurface portion 145 of the track is shown as being more obscured than surface portion 140.

[0088] Figure 3bAn overall view of an alternative arrangement of sensing circuitry 120 is shown, designed to cover a wider rectangular area rather than an elongated strip. The alternative arrangement includes a generally rectangular flexible substrate 125 and conductive tracks 130, 140 printed on the flexible substrate. A single positive track 130 extends around the perimeter of the substrate and includes a plurality of parallel finger portions that extend inward toward the central axis of substrate 125, perpendicular to the plurality of parallel fingers. Eleven ground tracks 140 include portions that extend along the central axis of substrate 125 and portions that include parallel finger portions that interdigitate with the parallel finger portions of positive track 130.

[0089] Figure 4 1 is a diagram of a leak detection system including a leak detector 110 and a plurality of sensing circuits 120. The leak detector 110 includes a processor 160 and a computer memory 170 storing computer-executable instructions. The processor 160 is in communication with the memory 170 and is configured to receive signals from the sensing circuits 120 and output an indication 150. The memory 170 stores computer instructions that, when executed by the processor, cause the processor to perform the methods described herein.

[0090] Figure 5 is a flow chart of an example of a method of operating the processor 160 of the leak sensor 110, wherein the leak sensor periodically executes a classification algorithm (such as Figure 6 or Figure 7 ) to determine the state of the leak sensor 110 and the environment in which the leak sensor is deployed. In this method, the leak sensor initially classifies the leak sensor as being in a "normal" state before waiting a set period of time. After the set period of time has elapsed, the leak sensor performs an analog-to-digital conversion (ADC) scan, measuring the impedance across each sensing circuit. While performing the scan, the leak sensor can measure the voltage difference between the two electrodes 136 and 146 of the sensing circuit, from which the impedance between these electrodes 136 and 146 can be deduced. After measuring the impedance across each sensing circuit, a classification algorithm (such as the one described below with reference to FIG) is used to determine the state of the leak sensor 110 and the environment in which the leak sensor is deployed. In this method, the leak sensor initially classifies the leak sensor as being in a "normal" state before waiting for a set period of time. After the set period of time has elapsed, the leak sensor performs an analog-to-digital conversion (ADC) scan, measuring the impedance across each sensing circuit. While performing the scan, the leak sensor can measure the voltage difference between the two electrodes 136 and 146 of the sensing circuit, from which the impedance between these electrodes 136 and 146 can be deduced. After measuring the impedance across each sensing circuit, the leak sensor is classified into the following categories: Figure 6 and Figure 7 The sensor may also perform a self-test sequence, wherein the sensor may check whether its battery voltage is low, whether its sensing circuit 120 is disconnected or damaged, whether its status indicates a significant leak, and / or the status of its internal circuitry for internal faults. If any of these checks identify a fault, the sensor may output a message 150 indicating the fault.

[0091] Figure 6 An example classification algorithm is shown in which a leak sensor is classified into a state based on the number of sensing circuits in the leak sensor whose impedance across the sensing circuits is below an impedance threshold. Multiple states are defined, each of which includes one or more possible numbers of sensing circuits below the impedance threshold. The illustrated example classification algorithm uses four states: State A, State B, State C, and State D, each corresponding to a corresponding number of sensing circuits below the impedance threshold. The maximum number of states is one plus the number of sensing circuits, allowing for a state in which zero sensing circuits are below the impedance threshold.

[0092] Each state (except the final state) has a corresponding threshold number of sensor circuits below the impedance threshold for moving to the next state with more sensor circuits below the impedance threshold. The threshold number of sensor circuits below the impedance threshold required to move from state A to state B is defined as T(A→B). Each state has a higher threshold than the state before it, such that T(A→B) <T(B→C)<T(C→D)。

[0093] In the initial step of the classification algorithm, the leak sensor's current state is identified, from which the threshold for moving to any adjacent state is determined. In the first evaluation, the leak sensor determines whether the number of sensor circuits below the impedance threshold is greater than or equal to the threshold for moving to the next state. If so, it moves to that state and outputs a message indicating the state change before terminating the classification algorithm.

[0094] exist Figure 6 In the example shown in , the initial state is determined to be stage B, so that in a first evaluation, it is determined whether the number below the impedance threshold ("wet electrode count") is greater than or equal to the threshold number to move from state B to state C (T(B→C)),

[0095] If the number of sensor circuits below the impedance threshold is not greater than or equal to the threshold for moving to the next state, then in a second evaluation, the leakage sensor determines whether the number of sensor circuits below the impedance threshold is less than the threshold for moving to the current state, and if so, moves to the previous state and outputs a message indicating the state change before ending the classification algorithm.

[0096] exist Figure 6 In the example shown in , if the number below the impedance threshold is not equal to or greater than T(B→C), then in a second evaluation, it is determined whether the number below the impedance threshold (“wet electrode count”) is less than the threshold number for moving from state A to state B (T(A→B)).

[0097] In an alternative embodiment, in the second evaluation, the number of sensor circuits below the impedance threshold may be compared to a specific threshold for moving to the previous state that is different from the threshold for moving from the previous state. For example, instead of comparing to (T(A→B)), the number of circuits below the impedance threshold may be compared to a threshold value T(B→A) (e.g., Figure 5 This can include hysteresis effects built into the system that bias the system toward resistance to moving to a less severe state, or can prevent the state of the system from changing rapidly in response to small changes in the number of sensing circuits whose impedance approaches an impedance threshold.

[0098] Alternatively or additionally, the threshold impedance may depend on the state of the system. For example, in states corresponding to more wet sensing circuits, the threshold impedance may be increased.

[0099] In other embodiments, after moving to a new state and / or sensing a message indicating a move to a new state, the system may return to the original step and repeat the evaluation for the new state, rather than exiting the evaluation. This may allow the state to change by multiple steps in a single evaluation without waiting for a preset time period to elapse, thereby allowing the system to respond to rapid changes in the number of wet sensing circuits. Alternatively or additionally, the system may be configured to move up or down more than one step at a time. That is, while Figure 6 A method for determining whether the number of times below the impedance threshold is within one of two ranges (moving up one state or moving down one state) is shown, but more ranges can be provided, each associated with a state. Thus, the method can determine whether the number of times below the impedance threshold is within one of a predefined number of ranges and set the state accordingly.

[0100] If neither the first nor the second evaluation results in a change of state, the leak sensor determines whether the time since it sent its most recent message is greater than a preset interval (such as the regular message interval RMI shown in the figure), and if so, outputs a message confirming the current state of the leak sensor. Regardless of whether such a message is output, the leak sensor then ends the classification algorithm.

[0101] If the current state of the leak sensor determined in the initial step of the classification algorithm is the highest state (state D in the example shown), then the first evaluation can be skipped, and if it is the lowest state (state A in the example shown), then the penultimate evaluation can be skipped.

[0102] Different states may correspond to different event types, such as no leak, and leaks of multiple different severities. Different classifications of leaks based on severity can enable more efficient allocation of resources when responding to messages indicating that a leak has occurred.

[0103] Figure 7 An example of a classification algorithm is shown in which a leak sensor is classified into a certain state based on the location on the sensing circuit where the leak occurs.

[0104] Multiple combinations of sensing circuits are defined, each of which includes one or more sensing circuits. The illustrated example classification algorithm uses four combinations: combination A, combination B, combination C, and combination D. The maximum number of combinations is 2 n , where n is the number of sensing circuits (including combinations without sensing circuits).

[0105] Each combination of sensing circuits corresponds to a specific event, such as leakage across a specific area spanned by the sensing circuits in that combination. For example, a combination consisting of a single sensing circuit in a specific area can correspond to the location of that sensing circuit on a wet substrate. In the illustrated example, combination A corresponds to event A, combination B corresponds to event B, and so on.

[0106] The algorithm involves evaluating whether the impedance across all sensing circuits in each combination is below an impedance threshold. If the impedance across all sensing circuits in a given combination is below the impedance threshold, an event or its identifier corresponding to that combination is added to the current state. These combinations are evaluated sequentially, and after all combinations have been evaluated, the leak sensor determines whether any events have been added to the current state or whether the current state is empty. If any events or their identifiers have been added to the current state, the leak sensor outputs a message identifying the event before concluding the classification algorithm.

[0107] If no events have been added to the current state and the current state is empty, the leak sensor determines whether the time since it sent its most recent message is greater than a preset interval. If so, it outputs a message confirming the current state of the leak sensor. Such a message can allow the user of the control system to determine that the leak sensor is operating correctly and is not detecting any leaks. Regardless of whether such a message is output, the leak sensor then ends the classification algorithm.

[0108] After running the classification algorithm as described above, the leak sensor may remain inactive for a set period of time before re-measuring the impedance across each sensing circuit and repeating the classification algorithm.

[0109] It will be appreciated that the conjunction "and / or" as used herein means one, some, or all of the options it connects. For example, a subject comprising features A, B, and / or C may comprise feature A, feature B, feature C, features A and B, features A and C, features B and C, or all of features A, B, and C.

[0110] While certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms. Furthermore, various omissions, substitutions, and modifications may be made to the specific embodiments described herein without departing from the scope of protection defined by the appended claims.

Claims

1. A method for detecting a liquid, the method comprising: receiving a plurality of signals, each signal indicative of a corresponding impedance across a respective sensing circuit of a plurality of sensing circuits, each sensing circuit configured such that the corresponding impedance across the sensing circuit changes when the sensing circuit is exposed to a liquid; for each sensing circuit of the plurality of sensing circuits, determining whether an impedance across the sensing circuit is within a predefined range of impedances; as well as In response to determining that the impedances of the set of the plurality of sensing circuits are each within the predefined range of impedances, an indication of liquid is output. The method according to claim 1 , wherein the predefined range is an impedance range below a threshold impedance.

3. A method according to claim 1 or claim 2, wherein the indication of liquid is an indication of the presence of liquid output in response to determining that the set includes at least a threshold number of sensing circuits.

4. The method according to claim 3, comprising: In response to the set including less than a threshold number of sensing circuits, an indication that liquid is not present is output.

5. A method according to claim 3 or claim 4, wherein the threshold amount is adjustable based on user input.

6. A method according to any preceding claim, wherein the indication of liquid is an indication of the presence of liquid output in response to determining that the set includes at least a threshold number of adjacent sensing circuits.

7. The method according to claim 6, comprising: In response to the set including less than a threshold number of adjacent sensing circuits, an indication that liquid is not present is output.

8. The method according to any one of claims 3 to 7, wherein: The threshold number is decreased in response to determining that the set includes at least a threshold number of sense circuits or at least a threshold number of adjacent sense circuits.

9. A method according to any one of claims 3 to 8, when dependent on claim 2, wherein The threshold impedance is lowered in response to determining that the set includes at least a threshold number of sensing circuits or at least a threshold number of adjacent sensing circuits.

10. A method according to any preceding claim, wherein: The indication of liquid is an indication of the presence of liquid output in response to determining that the number of sensing circuits in the set is within one of a plurality of ranges, and wherein the indication of the presence of liquid indicates the range within which the number of sensing circuits in the set is within.

11. The method of claim 10, comprising, in response to the set comprising less than a lowest limit of a lowest range of the plurality of ranges, outputting an indication that liquid is not present.

12. The method of claim 10 or claim 11, wherein the plurality of ranges comprises three or more ranges.

13. The method according to any one of claims 10 to 12, wherein: The one of the plurality of ranges is expanded in response to determining that the number of sensing circuits in the set is within the one of the plurality of ranges.

14. A method according to any preceding claim, wherein the indication of liquid is indicative of the identity or position of one or more sensing circuits in the set.

15. A method according to any preceding claim, wherein the method comprises: For each of a plurality of preset combinations of sensing circuits, determining for each sensing circuit in the preset combination whether an impedance across the sensing circuit is within the predefined range; and Wherein the indication of the liquid indicates the identity or location of each preset combination where the impedance across each sensing circuit in that preset combination is within the predefined range.

16. A method according to any preceding claim, wherein: For each sensing circuit of the plurality of sensing circuits: the predefined range of impedance to which the impedance across the sensing circuit is compared is an impedance range below a corresponding threshold impedance, and the corresponding threshold impedance is increased after determining that the impedance across the sensing circuit is below the corresponding threshold impedance; or The predefined range of impedance compared to the impedance across the sensing circuit is an impedance range greater than or equal to a corresponding threshold impedance, and the corresponding threshold impedance decreases after determining that the impedance across the sensing circuit is greater than or equal to the corresponding threshold impedance.

17. A method according to any preceding claim, wherein each sensing circuit of the plurality of sensing circuits comprises a pair of conductive tracks separated by a corresponding gap.

18. The method of claim 17, wherein each of the conductive tracks is printed in conductive ink on a substrate, and wherein each sensing circuit spans a different portion of the substrate. The method of claim 18 , wherein the conductive ink is insoluble in the liquid.

20. The method of claim 19, wherein the conductive ink is a carbon-based ink, and the liquid is water or an aqueous solution.

21. The method of any one of claims 18-20, wherein the substrate is an elongated strip, and wherein each sensing circuit spans a different portion of the length of the substrate.

22. A method according to any one of claims 17 to 21, wherein each of the conductive tracks is connected to a corresponding voltage through a circuit having a corresponding impedance, wherein the corresponding impedances are substantially equal to each other.

23. A method according to any one of claims 17 to 22, wherein each of the conductive tracks is connected to a corresponding voltage via a variable impedance circuit having a variable impedance, and wherein the method further comprises determining, for each conductive track, a corresponding impedance of the conductive track and configuring the corresponding variable impedance circuit to have the determined impedance.

24. A method according to any one of claims 17 to 23, wherein one of the conductive tracks is shared between a plurality of the plurality of sensing circuits.

25. A method according to any preceding claim, wherein it is periodically determined whether the impedance across each of the plurality of sensing circuits is within the predefined range.

26. A liquid sensor comprising a processor configured to perform the method of any preceding claim.

27. A storage medium comprising computer instructions executable by one or more processors, the computer instructions, when executed by the one or more processors, causing the one or more processors to perform the method according to any one of claims 1 to 25.

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