BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to the detection of leaks in fluid-containing conduits.

[0002] The present invention concerns leak detection in fluid-containing conduits. More particularly, but not exclusively, this invention concerns an apparatus for detecting leaks in fluid-containing conduits. The invention also concerns a kit and a method of detecting leaks in fluid-containing conduits.

[0003] There are many known ways of detecting leaks in fluid-containing conduits (typically buried water pipes or underfloor heating pipes), such as acoustic detection, infrared detection, hydrostatic testing and the use of tracer gas. Tracer gas is introduced into a pipe and leaks out into the surrounding substrate through any leak. The gas then diffuses through the substrate to the surface where it is detected. The gas may diffuse over a relatively large area, making precise location of the leak difficult. Infrared imaging is typically only of use for pipes containing relatively hot liquids, such as hot water. Acoustic testing often relies on the hearing of the operator to locate the leak before a meter is used to locate the precise location. This is obviously not desirable. Furthermore, a leak often has to be quite substantial in order to generate an acoustic signal. Hydrostatic testing involves trying to pressurise a pipe to relatively high pressures, which can be hazardous.

[0004] The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved apparatus and method of detecting leaks in fluid-containing conduits.

SUMMARY OF THE INVENTION

[0005] The present invention provides, according to a first aspect, an apparatus for detecting leaks in a buried fluid-containing conduit, the apparatus comprising: an electrical source for supplying a voltage to a fluid located in a fluid-containing conduit; a detector for detecting a potential difference or current resulting from leakage of electrical current from a fluid-containing conduit; and one or more ground-contacting probes, each being electrically connectable to the detector.

[0006] Embodiments of the apparatus facilitate the relatively rapid and precise detection of fluid leaks from fluid-containing conduits, in particular conduits containing electrically-conductive fluids, such as water. In use, a voltage typically of the order of kV is applied to a fluid in a conduit using the electrical source. Electrical current leaks out from the conduit leak point to the surrounding substrate, and this can be detected using the detector by placing the probes into contact with the ground. The potential difference across the probes is detected by the detector, either by measuring a current or a potential difference. The potential difference across the probes depends on the positon of the probes relative to the leak. The probes are directly above a leak when the potential difference detected by the detector is zero. Embodiments of the apparatus may facilitate the detection of slow fluid leaks.

[0007] The apparatus is similar to that used to locate breaks in electrical cable sheathing using the so-called “pool of potential” method. The applicant has discovered that, unexpectedly, it is possible to adapt the known apparatus to produce an apparatus which is capable of finding leaks in fluid-containing conduits.

[0008] The detector may be configured to reduce or reject low frequency signals.

[0009] Those skilled in the art will realise that the fluid and conduit are not part of the apparatus of the first aspect of the present invention.

[0010] The electrical source is optionally configured to generate a voltage sufficient to generate a detectable current in the presence of a fluid leak. The electrical source is optionally configured to generate a voltage of the order of kV. [0011] The electrical source is optionally capable of generating a voltage of at least 0.5kV, optionally at least lkV, optionally at least 2kV and optionally at least 3kV.

[0012] The electrical source is optionally capable of generating a voltage of up to l5kV, optionally up to l2kV, optionally up to lOkV and optionally up to 8kV.

[0013] The electrical source is optionally capable of delivering a current of up to lOOmA, optionally up to 75mA and optionally up to 50mA.

[0014] The electrical source is optionally capable of delivering a current of at least 2mA, at least 5mA and at least lOmA.

[0015] The output impedance of the electrical source is optionally at least 251<W, optionally at least 501<W, optionally at least 75kW and optionally at least 100kW.

[0016] The output impedance of the electrical source is optionally no more than 1MW, optionally no more than 750kD and optionally no more than 500kD. The applicant has found that it is possible for the electrical source to have a far greater output impedance than the source used to detect breaks in electrical cable sheath.

[0017] The electrical source may be capable of generating one or both of direct current (DC) and alternating current (AC), but is preferably capable of generating at least DC.

[0018] The electrical source is optionally capable of generating pulses of DC, preferably repeated pulses of DC, each pulse comprising a relatively high voltage applied for a first time period, TON, and a relatively low or zero voltage applied for a second time period, TOFF. Further characteristics of the pulse, TON and TOFF are described below in relation to the method of the third aspect of the present invention.

[0019] The electrical source and the detector may be arranged to be synchronised so that the detector indicates when the electrical source is on. This allows the user of the detector to ignore any signals which are not attributable to the output of the electrical source. Synchronisation may be achieved by providing each of the detector and the electrical source with a timer, optionally a resettable timer. The timers may be reset at the same time, thereby synchronising the timers. The detector’s timer is optionally coupled to an indicator, such as a visual indicator or an audible indicator. The detector’s timer can be configured to transmit a signal to the indicator when the electrical source is on, indicating to the user that the electrical source is transmitting a voltage. [0020] One or both of the power source and detector may be provided with one or both of a transmitter module for transmitting data and a receiver module for receiving data. For example, at least one of the power source and the detector may be provided with a transmitter module and at least the other of the power source and the detector may be provided with a receiver module. This allows at least one of the power source and detector to transmit data and the other of the power source and detector to receive data. For example, the power source may be provided with a transmitter module and the detector may be provided with a receiver module. The transmitter module may be configured to transmit a sync signal to the receiver module of the detector. Alternatively, the detector may be provided with a transmitter module and the power source may be provided with a receiver module. The transmitter module may be configured to transmit a start signal, the receiver module being configured to initiate the application of a voltage on receipt of the start signal. The detector and power source may each be provided with a receiver module, each configured to commence operation on receipt of a synching signal. Such synching signal may be provided by the apparatus (for example, by a sync transmitter) or by an external source, such as an external time signal.

[0021] The apparatus may be provided with one or more pulse input modules for input of one or more of TON, TOFF and a the ratio of TON: TOFF. One or both of the detector and power source may be provided with a pulse input module. A pulse input module may be coupled to a transmitter module to facilitate sending of pulse information to a receiver module via a transmitter module. A pulse input module may be coupled to a receiver module to facilitate receipt of pulse information.

[0022] The detector may comprise an AC-coupled detector, for example. Alternatively or additionally, the detector may comprise a signal processor to reduce or reject low frequency signals, such as DC. The detector may provide a non-linear response. For example, the detector may have increased sensitivity (i.e. a larger change in output signal for a given change in input signal) around the zero volt mark.

[0023] The detector may provide a substantially logarithmic response. The provision of a logarithmic response is a way of increasing dynamic range. The detector may comprise a log amplifier. The detector may comprise an instrumentation amplifier coupled to a circuit for providing a non-linear response based on the output of the instrumentation amplifier. In this case, the output of the instrumentation amplifier may be coupled to the input of the circuit for providing a non-linear response. The circuit for providing a non linear response may produce a larger change in signal for a given change in voltage around the zero volt mark. Said circuit may comprise a log amplifier. Alternatively or additionally, the detector may be configured to change sensitivity according to signal amplitude (for example, auto-ranging as observed in a multi-meter). For example, sensitivity could be lower for lower signal amplitudes.

[0024] The apparatus may comprise two (and only two) ground-contacting probes. Optionally, the apparatus may comprise three probes, one of which provides a reference potential for the detector.

[0025] Each of the one or more probes may be a ground-penetrating probe. The surface of the ground-penetrating or ground-contacting portion of each probe typically comprises the same conductive material. This reduces the likelihood and/or magnitude of a potential difference developing between the probes on account of the surface-contacting portion being made of different conductive materials. The surface of the ground-penetrating or ground- contacting portion of each probe typically comprises an inert conductive material, such as silver, gold and/or platinum. Probes which are merely ground-contacting and not ground penetrating would typically have rounded or flattened ends to facilitate contact with the ground. Probes which are ground-penetrating (and ground-contacting by definition) would typically have tapered or pointed ends to facilitate insertion into the ground.

[0026] The apparatus may comprise a support to which one or more of the probes and optionally the detector are attached. The support may be in the form of a frame. This facilitates movement of the probes and detector together and therefore facilitates rapid location of a leak. Optionally, two probes and the detector are attached to the support.

[0027] The electrical source may comprise at least two outputs (typically a positive and a negative output), at least one of which (typically the negative output) is attached to a grounding contact, such as a grounding spike. The grounding contact optionally facilitates the formation of a circuit which may be beneficial. The positive output is typically used to provide the output electrical signal. The electrical source is optionally earthed, for example, via an earthing cable and earthing contact (which may be, for example, in the form of an earthing spike), optionally in addition to the grounding contact. The earthing cable may optionally be attached to an electrical source earthing point. In use, the earthing contact may form an earthing connection proximate to the power source so that the grounding contact attached to the positive or negative output need not be located close to the power source. The grounding contact attached to the positive or negative output may be located remote from the detector. In this connection, it is preferred that the distance between the detector and the leak is less than half of the distance between the leak and the grounding contact, and when positioning the grounding contact, it is therefore desirable to have the size and location of the search area in mind. It is beneficial to locate the earthing contact proximate to the power source to protect a user close to the power source.

[0028] The potential difference between the grounding contact and the earthing contact may optionally be monitored so that there is no dangerous current generated between the two. Therefore, the electrical source may be provided with a potential difference monitor for monitoring the potential difference between the output (typically the negative output) and the earthing point. The potential difference detector may be configured to operate a cut-out circuit which cuts the output of the electrical source in the event that the potential difference monitor monitors a potential difference above a pre-determined level (for example, 40V). The electrical source may comprise a switch which connects the grounding output and the earthing output in the event that the output voltage is turned off. The electrical source may also comprise a switch which connects the other of the outputs and the earthing point in the event that the output voltage is turned off.

[0029] According to a second aspect of the invention there is also provided a kit for assembly into an apparatus in accordance with the first aspect of the present invention, the kit comprising an electrical source, a detector configured to reduce or reject low frequency signals and for detecting a potential difference or current resulting from leakage of electrical current from a fluid-containing conduit and one or more probes. [0030] The kits may comprise instructions for use of one or more of the electrical source, the detector and one or more probes.

[0031] The components of the kit of the second aspect of the present invention may comprise those features described above in relation to the apparatus of the first aspect of the present invention.

[0032] According to a third aspect of the invention there is also provided a method of detecting a fluid leak in a buried fluid-containing conduit, the method comprising:

Providing a voltage to the fluid contained in the conduit; and

Sensing for leakage of electrical current from the conduit.

[0033] The method of the third aspect of the present invention has been found to be effective in locating fluid leaks in buried pipes, such as water pipes. The applicant has discovered that, unexpectedly, the so-called“pool of potential” method which is used to detect defects in the sheaths of electrical cables may be used to detect fluid leaks in fluid- containing conduits. The voltage applied is typically sufficiently large to produce a detectable current in the presence of a fluid leak. This may vary from case to case, and may depend, for example, on the conductivity of the fluid. The fluid is optionally a liquid.

[0034] Sensing for leakage of electrical current may comprise providing at least one electrical contact (optionally two electrical contacts, and optionally more electrical contacts) with the ground in proximity to, and optionally above, the conduit. Such electrical contact(s) may be in electrical connection with a detector. Each electrical contact may, for example, be associated with a ground-contacting or ground-penetrating probe.

[0035] The fluid is preferably an electrically-conductive fluid, such as an electrically- conductive liquid. The fluid may be an aqueous fluid (i.e. a fluid comprising water). In the event that the fluid is not sufficiently electrically-conductive, then it may be necessary to provide an electrical conductor within said conduit. Such an electrical conductor is optionally elongate, and is optionally arranged along a length of the conduit to be tested.

[0036] The fluid is optionally a liquid. [0037] The conduit is typically electrically non-conductive. For example, the conduit may be plastic, for example. This permits detection of the leak, since the leak effectively provides an electrically-conductive path out of the otherwise electrically-insulating conduit. There may be (generally relatively small) portions of the conduit which are effectively electrically conductive (for example, portions fitted with metal clamps or connectors). If necessary, metal parts such as fittings which may cause a problem may be removed from the conduit, if desired.

[0038] The voltage may be a DC or AC voltage. It is preferred that the voltage is a DC voltage because it is thought that the use of AC voltage may lead to capacitive losses.

[0039] The method may comprise applying a pulsed DC voltage. For example, the method may comprise applying a relatively high DC voltage for a first period (TON), and applying no or a relatively low DC voltage for a second period (TOFF). This sequence of applying a relatively high voltage, followed by a relatively low voltage may be repeated to provide a train of pulsed DC voltages. The ratio of TON: TOFF may be less than 1 : 1, optionally less than 1 :2, optionally more than 1 :6, optionally more than 1 :5, optionally more than 1 :4, optionally from 1 :4 to 1 :2 and optionally about 1 :3. This ratio have been found to be effective in allowing readings to be taken. It is anticipated that lower ratios of TON: TOFF may be beneficial for larger pipes because such larger pipes take a longer time to discharge.

[0040] TON is optionally at least 0.5 second and optionally at least 1.0 second. TON may be less than 5.0 seconds, optionally less than 3.0 second and optionally less than 2.0 seconds. TON may optionally be from 1.0 to 2.0 seconds, optionally about 1.5 seconds.

[0041] The voltage may be applied using an electrical source which may have the features described above in relation to the apparatus of the first aspect of the present invention.

[0042] The voltage applied to the fluid may optionally be at least 0.5kV, optionally at least lkV, optionally at least 2kV and optionally at least 3kV. For example, the voltage applied to the fluid may be a DC voltage of at least 0.5kV, optionally at least lkV, optionally at least 2kV and optionally at least 3kV. The DC voltage may be pulsed, as described above. For the avoidance of doubt, the voltage values stated in relation to a pulsed DC voltage refer to the voltages of the pulse itself (and not an averaged or weighted voltage).

[0043] The current supplied may be at least 3mA, optionally at least 5mA and optionally at least lOmA. The current supplied may be no more than lOOmA, optionally no more than 75mA and optionally no more than 50mA.

[0044] The method may comprise sensing a current or potential difference.

[0045] The method may comprise sensing a current or potential difference as a function of position along said conduit. The method may therefore comprise sensing a current or potential difference in a first position along said conduit, and sensing a current or potential difference in a second position along said conduit. The method may comprise sensing a current or potential difference using one or more probes (typically two probes). The probes may be as described above in relation to the apparatus of the first aspect of the present invention. Two probes may be used to provide a differential input to a detector. If one probe is used, the probe may be used to provide an input to a single-ended input of a detector.

[0046] Sensing a zero or minimum value (in magnitude) in said current or potential difference may be indicative of the location of the leak.

[0047] The sensing may be performed using any suitable detector. The sensing may be performed using a detector such at that described above in relation to the apparatus of the first aspect of the present invention.

[0048] The method of the third aspect of the present invention may use the apparatus of the first aspect of the present invention.

[0049] The method may comprise providing at least one earthing or grounding connection from the electrical source. The method may comprise contacting an earthing or grounding contact with the ground. This may involve, for example, inserting a grounding or earthing spike into the ground. The method may comprise providing at least two earthing or grounding connections from the electrical source. The method may comprise contacting at least two earthing or grounding contacts with the ground. The method may comprise providing a first grounding or earthing connection from an output of the electrical source (typically the negative output). The method may comprise providing a second grounding or earthing connection. The second grounding or earthing connection optionally forms a connection from a housing or casing of the electrical source. The first grounding or earthing connection optionally comprises forming a first grounding contact with the ground, typically remote from any detector being used for detecting leaks i.e. typically remote from the position of sensing for the leakage of current. In this connection, it is desirable for the distance between the detector and the leak to be less than half of the distance between the leak and the first grounding contact with the ground. Therefore, the positioning of the first grounding contact with the ground should be performed, bearing in mind the size of the prospective search area and prospective position of a leak. The second grounding or earthing connection comprises forming a second grounding contact with the ground, typically proximate to the power source to provide earthing protection for a user close to the power source. In use, the second connection is typically visible to any user, whereas the first connection may not be.

[0050] The method may comprise providing a DC voltage to the fluid in the conduit and sensing for a leakage of electrical current. The DC voltage may be provided for a period of at least 5 seconds, optionally for at least lOs, optionally for at least 20s, optionally for at least 30s, optionally for at least 30s, optionally for at least 40s, optionally for at least 50s and optionally for at least 60s. The DC voltage may be provided for no more than 5 minutes, optionally for no more than 4 minutes, optionally for no more than 3 minutes and optionally for no more than 2 minutes. The DC voltage is optionally at least lkV, optionally at least 2kV, optionally at least 3kV, optionally at least 4kV and optionally at least 5kV. The application of a relatively large DC voltage for a relatively long period of time facilitates the detection of the presence of a fluid leak, but not necessarily the location of the leak. The method may therefore also comprise sensing for the location of a leak. In this connection, the method may comprise providing a DC voltage to the fluid and sensing for a leakage of electrical current, as indicated above to determine the presence of a fluid leak, and if a fluid leak is detected, applying a suitable electrical signal to the fluid in the conduit and sensing a current or potential difference as a function of a position along the conduit. The suitable electrical signal may, for example, by a pulsed DC signal.

[0051] In accordance with a fourth aspect of the present invention, there is provided a method of detecting a fluid leak in a buried fluid-containing conduit, the method comprising: applying a voltage to a point source of electrical potential located within the conduit; and sensing for leakage of electrical current from the conduit.

[0052] The point source may typically comprise a small portion of naked conductive material,“naked” indicating that the conductive material is not covered by an electrical insulator. The point source is typically connected to an electrical source by a sheathed cable or wire. The voltage required is typically sufficiently large to generate a current in the presence of a fluid leak. The method may comprise sensing for leakage of electrical current from the conduit as a function of the position of the point source within the conduit. A potential difference is generated at the point source, and any current leakage local to the point source may be detected for sensing for leakage of electrical current from the conduit. If no or little current leakage is observed, then this is indicative of there being no local leakage of fluid from the conduit. The detection of local current leakage local to the point source may be indicative of there being local leakage of fluid from the conduit.

[0053] The method may comprise moving the point source and the probes, and sensing for leakage of electrical current from the conduit.

[0054] The method of the fourth aspect of the present invention may comprise using the apparatus of the first aspect of the present invention, in conjunction with a small portion of naked conductive material electrically connected to the source of voltage, optionally with a sheathed cable or wire.

[0055] In accordance with a fifth aspect of the present invention, there is provided a method of detecting a fluid leak in a buried fluid-containing conduit, the method comprising: applying a voltage to an elongate electrical conductor located within the conduit, at least an elongate portion of which is exposed, thereby permitting contact between the electrical conductor and the fluid; and sensing for leakage of electrical current from the conduit.

[0056] The method of the fifth aspect of the present invention may be of particular use if the fluid in the conduit is of a low electrical conductivity. The voltage required is typically sufficiently large to generate a current in the presence of a fluid leak. The method of the fifth aspect of the present invention provides an elongate electrical conductor proximate to the location of the leak, and therefore provides a high potential difference close to the leak site. Most of, and substantially all of, the elongate electrical conductor may be exposed. In this case, the elongate electrical conductor may, for example, comprise a bare wire. This provides a linear source of voltage within the conduit. For reasons of safety, the elongate electrical conductor may comprise a header portion which is covered with electrically- insulating material. The header portion may, in use, be located proximate to the electrical source, and therefore be accessible to users. The method of the fifth aspect of the present invention may be achieved using the apparatus and kit of the first and second aspects of the present invention, respectively, but further comprising an elongate electrical conductor, at least an elongate portion of which is exposed. The term“exposed” indicates that the electrical conductor is exposed so that when immersed in a fluid, the electrical conductor contacts the fluid. The exposed portion would typically be bare wire, for example. The method of the fifth aspect of the present invention may use the method steps of the method of the third aspect of the present invention in order to determine the location or position of a leak.

[0057] The electrical conductor typically comprises a wire which is physically robust enough to be threaded through the conduit. Electric fencing wire may be used, for example; such wire comprises a plastic, non-conductive substrate which supports one or more electrically-conductive filaments or threads. [0058] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, any of the methods of the invention may incorporate any of the features described with reference to the apparatus of the present invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0060] Figure 1 shows a schematic view of an apparatus for detecting leaks in a fluid- filled conduit according to a first embodiment of the invention;

[0061] Figure 2 shows a front-on view of a detector mounted on a probe-bearing frame, as used in the apparatus of Figure 1; and

[0062] Figure 3 shows a schematic representation of a method of detecting a leak in a fluid-filled pipe according to a second embodiment of the invention;

[0063] Figure 4 shows a schematic representation of the detector used in the apparatus of the first embodiment of the invention;

[0064] Figure 5 shows a schematic representation of the detector response as a function of position relative to a leak in a fluid-filled conduit;

[0065] Figure 6 shows a schematic representation of a method of detecting a leak in a fluid-filled pipe according to a further embodiment of the invention, the method using a movable probe;

[0066] Figure 7 shows a schematic representation of a method of detecting a leak in a fluid-filled pipe according to a further embodiment of the invention, the method using a bare metal wire; and

[0067] Figure 8 shows a schematic representation of an electrical source which is used in a further embodiment of the apparatus and method of the present invention. DETAILED DESCRIPTION

[0068] An embodiment of an apparatus in accordance with the present invention and an embodiment of a method in accordance with the present invention will now be described with reference to Figures 1 to 5. An apparatus for detecting leaks in a fluid-filled conduit is denoted generally by reference numeral 1. The apparatus 1 comprises an electrical source 2 for applying a high voltage (of the order of kV) to a fluid F provided in conduit C. The fluid in this case is water. The conduit is a buried water pipe made from a plastics material. An A. C. -coupled detector 3 is used to detect any current leaking into the ground from conduit C. Leakage of electrical current occurs around fluid leak L, and therefore a current is detectable by detector 3 when proximate to leak L. This is described in more detail below.

[0069] The electrical source 2 is capable of producing a DC voltage of 6kV, and a maximum current of 30mA (the output impedance therefore being 2001<W). The source comprises several safety features, including a light indicating that electrical power is being provided to the electrical source, a light indicating that the electrical source is generating a voltage, a key switch and an activation switch. The electrical source 2 is configured to generate a DC high voltage for about 1.5s (l .398s) after which the voltage is turned off for about 4.5s (4.194s). This cycle is repeated. The electrical source is similar to the S271T transmitter available from Bicotest Limited (htt>://www.bicotest. eo.uk/datasheet/s5000.pdf) and the transmitter used in the Locator SFL1 Sheath Fault Tester system (htt>s://www.thener _.K ie.eom/products/cabie-fault- loeation-instruments/sheath-fault-tester/) .

[0070] Each of the electrical source 2 and the detector 3 is provided with a resettable timer (not shown). The resettable timers are reset at the same time, thereby synchronising the timers. This synchronisation, coupled with knowledge of the voltage on/off timings, may be used to display to indicate to the detector user when the high voltage is applied. In this connection, the detector 3 comprises a signalling lamp (not shown) which is in communication with the detector’s resettable timer so that when the electrical source is on, the signalling lamp is illuminated. This enables the user of the detector 3 to ignore any detector signals which are not associated with the high voltage being applied. Those skilled in the art will realise that a sounder could be used in addition, or as an alternative to, the lamp.

[0071] Other values of TON (the duration of the DC voltage) and TOFF (the time for which there is zero voltage between DC pulses), and other ratios of TON: TOFF may be used. One or both of the detector 3 and power source 2 may be provided with switches for selecting pulse characteristics, such as TON, TOFF and the ratio TON: TOFF. The detector 3 and power source 2 may also be provided with transmitter and receiver modules for the transmission and receipt of data, including such pulse characteristics. Any suitable data transmission and reception system (e.g. WiFi, Bluetooth) may be used. Such an arrangement may be used to synchronise the electrical source 2 and detector 3.

[0072] The electrical source 2 is electrically coupled to a clip (now shown). The clip is attached to a small metal pipe which is immersed in the fluid F contained in the conduit C, typically at or near an end of the conduit C. If both ends of conduit C are accessible, then voltage may be applied at both ends of the conduit C using a similar arrangement. If the conduit itself comprises metal portions which are in contact with the fluid F, then the clip may be attached to one of those metal portions.

[0073] The detector 3 effectively measures the potential difference between two probes 4a, 4b. The probes 4a, 4b are configured to be inserted into ground above a conduit C. The probes 4a, 4b are each mounted on a leg 7a, 7b of a frame 6. Each probe 4a, 4b is coated with the same electrically-conductive, inert material (in this case, silver). A current generated between the probes 4a, 4b is detected by detector 3. A signal representative of the potential difference between the two probes 4a, 4b is provided to an instrument amplifier 31 whose output is coupled to the input of a log amplifier 32. The output of the log amplifier 32 is fed to an analogue meter 33 for display. Those skilled in the art will realise that the output of the log amplifier 32 is non-linear in that for relatively small changes in input signal close to zero, the change in output is relatively large. This is beneficial because, as described below, when the probes 4a, 4b are close to the leak L, then the potential difference across the probes 4a, 4b is relatively small. The detector 3 is an AC-coupled detector to remove DC signals which would affect the stability of the signal to the meter 33. In this connection, it has been found that a small DC signal of the order of a few tens of millivolts exists between the two probes 4a, 4b when the probes are first inserted into the ground. This signal takes an unacceptably long time (of the order of several tens of second) to stabilise. AC-coupling removes the DC signal and allows measurements to be recorded more quickly. Furthermore, a pulsed DC signal is applied to the fluid F in the conduit C to generate a reading in the meter 33. The switching on of the DC signal generates a first reading (in the form of the meter needle flicking in one direction by a certain amount) and the switching off of the DC signal generates a second reading (in the form of the meter needle flicking in an opposite direction to the first reading by a certain amount). Those skilled in the art will realise that a digital meter could be used instead of an analogue meter. The detector 3 is battery-powered.

[0074] In the present case, the detector scale is non-linear, with full (100%) deflection corresponding to approx. 25mV, and 10% deflection corresponding to 0.16mV. The impedance between the probes is about lOOkOhm, and the time constant of the AC coupling is 0.22secs.

[0075] The method 100 will now be described in more detail below with reference to Figures 1 to 5. The method 100 comprises applying 101 a voltage (typically 6kV), with a testing current of about 5-10mA to the fluid F using the electrical source 2. The maximum (short circuit) current which can be delivered by the electrical source is 30mA. The electrical source 2 is coupled to the fluid F using a short length of copper pipe (not shown). The detector 3 is used to measure the potential difference across probes 4a, 4b as a function of the probes’ position along the length of the conduit C. the probes are inserted into the ground above the conduit C before a reading is taken. The potential difference across the probes 4a, 4b depends on the presence of a leak and on the location of the probes relative to the leak. In the absence of a leak, the potential difference across the probes should be substantially zero. In the presence of a leak, the potential difference may be substantially zero if the probes are sufficiently far from the leak or directly above the leak. However, in the event that probes are not too remote from the leak, then a signal will be registered. In this connection, Figure 5 shows a schematic representation of the potential difference across the probes as a function of displacement of the probes from a leak L. Therefore, in our example, as the probes are moved towards the leak, the signal shown by the detector 3 will increase to a maximum and then decrease rapidly towards zero. If the probes are moved past the leak L, then the signal generated by the detector 3 will increase in magnitude rapidly to a minimum point, and then decrease in magnitude as the probes 4a, 4b are moved away from the leak L. When the probes are directly above the leak the potential difference between the probes 4a, 4b is nil. Therefore, when the probes are placed one side of a leak (for example, approaching a leak), the detector signal has a certain sign (positive or negative). When the probes are directly over the leak L, the detector reading is zero. When the probes are placed the other side of a leak (for example, going beyond the leak), then the detector signal has a sign which is opposite to that observed when the probes are placed approaching the leak. The detector 3 comprises a log amplifier 32 which generates a relatively large output signal for a relatively small input signal around the zero mark, which is beneficial in the present case.

[0076] Typically, during a test the probes are moved about 3 m between each reading along a straight line (e.g. north-south), with smaller probe movements being made around the zero point (the leak L). When this first zero point has been found, the probes are moved along a line at right angles to the first line of movement (e.g. east- west), and another zero position found. By repeating the probe movements at right angles to one another the position of the leak can be located very accurately.

[0077] By moving the probes around the nil or zero point it is possible to detect the leak L quickly and with accuracy.

Example 1

[0078] Testing has been carried out on lOOm long, buried, water-filled plastic pipes, of 32mm diameter and 50mm diameter. The pipes when in good condition (i.e. unpunctured) withstood 6kV without any measurable current flowing, using a lOmA meter for the measurement. Leaks were introduced into each pipe with the point of a Stanley knife about 30m from the end of each pipe. Once leaks had been introduced, a current of ~5mA was detected with 6kV applied. The pipes were laid l.2m deep, in a loop formation that brought the ends close together where they came out of the ground. The leak was detectable from about 4m from the pipe. The position of the leak could be pinpointed within a few minutes (15) of probing the site.

Example 2

[0079] Testing was been carried out on a ground source heat-pump system that had been leaking approximately 2- 3 litres of coolant a week since it was installed. The Heat-pump machinery was disconnected from the system as its metal parts are connected to ground. This was done by cutting copper pipes just beyond the point where they connected to the plastic pipes buried in the ground, leaving about 30cm of copper pipe on each plastic pipe. It was also possible to make the two pieces of copper pipe vertical, so that they could have the coolant level part-way up their length, and so provide the electrical connection to the coolant using the copper pipe.

[0080] The first probe position interrogated was close to the point where the pipes came out of the ground, to check that there was no current flowing in dampness on the outsides of the pipes. Once this had been established, the ground was probed at approximately 3m intervals along the pipe route. An indication of a leak was found at, for example, the 4 ^th probing position, with the strength of the detector indication increasing at, for example, the 5 ^th probing position, with the sign of the detector reading reversing at, for example, the 6 ^th probing position.. It was then a matter of probing between the 5 ^th and 6 ^th positions to find the zero point. A few positions at lm intervals (then 0.5m, then 0.25m etc), along this first line of probing and then at right-angles to the first line of probing allowed rapid pinpointing of the leak location. Upon digging down to the pipe, a leaking elbow fitting was found. After the soil was cleared from around the fitting and the pipe dried for about 30cm each side of the fitting, there was no indication of a leak, as the leak was electrically isolated from the soil. The slow drip of coolant from the elbow was of no concern. Finding the leak location took approximately 15 minutes once the pipes were prepared and the voltage generator connected. [0081] An arrangement of the electrical source 2 will now be discussed in more detail with reference to Figure 8. The positive output 401 of electrical source 2 is connected via an output cable 402 to a short length of copper pipe 403 which is immersed in a liquid in pipe P. The negative output 404 of electrical source 2 is attached via output cable 405 to a grounding spike 406, thereby completing the output circuit of electrical source 2. During use, current flows between the positive output cable 402 and the negative output cable 405.

[0082] The case 407 of electrical source 2 is connected, via an earthing cable 408 connected to an earthing point 408a on case 407, to earth spike 409. Earth spike 409 provides an earthing connection to electrical source 2. Furthermore, earth spike 409 may be located close to, and in direct sight of, the user who is operating the power source 2 (not shown in Fig. 8). The location of an earthing connection close to the detector- operating user is important because it reassures the user that the electrical source 2 is appropriately earthed. Furthermore, the earthing of electrical source 2 using the earthing cable 408 and earth spike 409 permits grounding spike 406 to be located a desired distance (such as at least lOOm, for example) from a user operating the detector 3. In deciding where to place the grounding spike 406, the size and position of the prospective search area should be considered, taking into account that it is desirable for the distance between the detector 3 and the leak should be less than half the distance between the leak and the grounding spike 406.

[0083] The electrical source 2 is provided with a voltage detector 410 which detects the potential difference between grounding output 408a and the negative output 404. The voltage detector 410 is coupled to a cut-out circuit 411 which is arranged to cut-out the output of electrical source 2 in the event that the potential difference detected by the voltage detector is greater than 40V. This prevents the establishment of a potentially dangerous potential difference between the grounding spike 406 and the earthing spike 409.

[0084] Furthermore, a relay contact 412 is provided which connects the earthing point 408a and negative output 404 when there is no output from the electrical source 2 so that there is no potential difference between the negative output 404 and earthing point 408a. [0085] The method of the present invention will typically be used for detecting leaks in conduits containing conductive liquids, such as water. Some embodiments of the method of the present invention have been able to detect very slow leak rates of the order of several litres per week.

[0086] The method described above is essentially the same as the“pool of potential” method that is used to locate breaks in electrical insulation which sheathes electrical cables. That method is disclosed in“Fault location in the outer sheath of power cables”, Q. Wang et al., Journal of Power Technologies, vol. 94(4), 2014, pages 250-258.

[0087] Those skilled in the art will realise that in order for the method of the present invention to work, the conduit C has to be substantially electrically non-conductive in order for the leak L to be locatable. It is possible to use the method of the present invention on pipes which have conductive portions (for example, metal pipe connectors), so long as the portion of the pipe having leak L is electrically non-conductive. In certain circumstances, it may be desirable to remove some metal fittings, or to remove soil from around such fittings; some metal fittings may give the same signal as a leak if the surrounding soil is not removed or if the fitting is not removed.

[0088] An exemplary embodiment of a method in accordance with the fourth aspect of the present invention will now be described with reference to Figures 1 and 6. A point source of potential (not shown, but a metal rod with an exposed end) is attached to the electrical source 2 by a sheathed electrical cable (not shown), and inserted into the conduit C. The exposed end of the rod effectively acts as a point source of voltage, and is moved along the conduit C, with the detector 3 being moved along the length of the conduit C to try to find leak L. The exemplary method is denoted generally by reference numeral 200 and comprises providing 201 a voltage (typically of the order of kV) to the point source and sensing 202 for leakage current using detector 3 associated with leakage of fluid F from conduit C. The detector 3 and rod are then moved 203 along conduit C and a voltage of the order of kV applied 204 to the rod. The detector 3 is used to sense 205 any current associated with leakage of fluid F from conduit C. The method 200 is very similar to that described above in relation to Figures 1 to 5, in that the detector 3 is moved along the conduit C, making measurements of current as a function of the position of the detector 3 along the conduit C, except that the rod is also moved along the conduit. As for the method 100 described above in relation to Figures 1 to 5, the detector 3 is above the leak when there is a zero reading from the detector 3. This method may be more sensitive than the method 100 described above because the detector 3 is located proximate to the source of high voltage (the end of the rod), and may be used if the fluid F contained in the conduit C is of a low electrical conductivity.

[0089] An exemplary embodiment of a method in accordance with the fifth aspect of the present invention will now be described with reference to Figures 1 and 7. A wire (not shown) is attached to the electrical source 2, and inserted into the conduit C. The wire is a length of electric fencing wire having a diameter of about 2mm and which comprises a plastic, non-conductive substrate which supports three strands of 0.15mm metallic threads (typically stainless steel). If the approximate position of the leak is not known, then the wire is inserted along the whole length of the conduit. If the approximate position of the leak is known, then the wire need only reach the vicinity of the leak. The wire effectively acts as a line source of voltage, with the detector 3 being moved along the length of the conduit C to try to find leak L. The exemplary method is denoted generally by reference numeral 300 and comprises providing 301 a voltage to the wire (typically of the order of kV) and sensing 302 for leakage current using detector 3 associated with leakage of fluid F from conduit C. The detector 3 is then moved 303 along conduit C and a voltage (typically of the order of kV) applied 304 to the wire. The detector 3 is used to sense 305 any current associated with leakage of fluid F from conduit C. The method 300 is very similar to that described above in relation to Figures 1 to 5, in that the detector 3 is moved along the conduit C, making measurements of current as a function of the position of the detector 3 along the conduit C. As for the method 100 described above in relation to Figures 1 to 5, the detector 3 is above the leak when there is a zero reading from the detector 3. This method may be more sensitive than the method 100 described above because the detector 3 is located proximate to the source of electrical potential(the wire), and may be of use if the fluid F is of low electrical conductivity. [0090] The method described above in relation to Figures 1 and 7 may be adapted, for example, by introducing the wire into the conduit C while the conduit is empty or at least not filled, and then filling the conduit C with an appropriate fluid afterwards.

[0091] The methods above describe the location of leaks in a conduit. The location/pathway of the pipe may be determined by using methods known to those skilled in the art. For example, a Sondes transmitter may be inserted into the pipe, with the signals emitted by the transmitter being detected by a Cat and Genny detector.

[0092] A further exemplary embodiment of a method in accordance with the method of the third aspect of the present invention will now be described. The apparatus described above is used to detect a suspected leak in a ground source heat pump system. Briefly, an electrical connection is established with a metal part of the heat pump manifold (not shown). A high DV voltage (about 6kV) is applied to the fluid in the ground source heat pump system using the electrical connection for about 2 minutes, while a ground contacting probe is used to detect leakage of electrical current from the ground source heat pump system. In the event that leakage of electrical current is detected, then this indicates leakage of fluid from the ground source heat pump system. If a leak is indicated, then the position of the leak along the conduit is determined substantially as described above, using a pulsed DC signal (6kV, pulsed). The manifold is generally easily accessible and therefore this method is a convenient way of, firstly, detecting a leak and, secondly, detecting the position of the leak along the conduit.

[0093] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0094] The method described above relates to the use of an apparatus in accordance with the first aspect of the present invention. Such an apparatus uses an A. C. -coupled detector. Those skilled in the art will realise that other types of detector may be used. For example, a detector may comprise a signal processor which removes or reduces low frequency signal components. [0095] The method and apparatus described above use two probes to provide a differential input to a detector. Those skilled in the art will realise that one probe may be used, for example, to provide a single-ended input to a detector. Those skilled in the art will realise that more than two probes may be used, for example, three probes may be used, one of which is used to provide a reference signal.

[0096] The example above describes the detection of a leak in a water pipe and in a ground source heat-pump system. Those skilled in the art will realise that the apparatus and method may be used for other liquid-containing conduits.

[0097] The examples above describe the use of pulsed direct current to locate the leak. Those skilled in the art will realise that alternating current may be used, although direct current may be preferred because of possible loss of voltage along the length of a conduit due to capacitive losses.

[0098] The examples above show the use of ground-penetrating probes. It would be possible to use probes which contact the ground, but do not penetrate the ground. For example, such probes may have flattened ends for establishing contact with hard ground surfaces which are difficult to penetrate.

[0099] Those skilled in the art will realise that different power supply may be used. For example, a power supply producing 6kV and 58mA may be used.

[00100] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.