Fault detection for medical apparatus

Abstract

A fault detection device (60) is provided for a medical apparatus (10), which is powered by connection to live and neutral power wires (31, 32) and is operable to define a fluid flow path (20) that contains an electrically conductive fluid and extends between an individual (P) and a drain (40). The fault detection device (60) is operated to measure a first value indicative of a voltage level at a sensing element (63) in electrical contact with the electrically conductive fluid in the fluid flow path (20) while establishing a conducting wire path from the sensing element (63) to the neutral power wire (32) via a resistor device, measure a second value indicative of the voltage level at the sensing element (63) while breaking the conducting wire path, and evaluate the first and second values for detection that the individual (P) is in physical contact with mains power (50).

Description

[0001] FAULT DETECTION FOR MEDICAL APPARATUS

[0002] Technical Field

[0003] The present disclosure relates generally to electrical equipment for medical use, and in particular to a technique of detecting when an individual connected to the electrical equipment is at risk of being subjected to harmful leakage currents. The technique is, for example, applicable to electrical equipment for dialysis therapy.

[0004] Background Art

[0005] Dialysis therapy is undertaken to replace or supplement the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is known as kidney failure and includes acute kidney injury (AKI) and chronic kidney disease (CKD). Dialysis therapy involves removal of water from the body of the patient suffering from kidney failure, as well as exchange of solutes with the patient's blood. One example of dialysis therapy is peritoneal dialysis (PD), in which a treatment fluid is infused into the peritoneal cavity of the patient to interface with the blood of the patient through the peritoneal membrane. Another example of dialysis therapy is extracorporeal (EC) blood therapy, in which blood is circulated outside of the patient and interfaced with one or more treatment fluids. Modalities of extracorporeal blood therapy include hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF).

[0006] Treatment fluids used in PD and HD are commonly known as dialysis fluids. In HF, the treatment fluid is known as replacement fluid, since it is infused into the blood of the patient to replace fluid removed during therapy. In HDF, both dialysis fluid and replacement fluid are used.

[0007] Dialysis therapy may be automated by use of machines, i.e. electrical equipment. Such electrical equipment produces leakage currents. There are standards for safety and performance of medical electrical equipment. One such standard is IEC60601, which defines maximum leakage currents allowed in electrical medical equipment to reduce the risk of electrical shock based on type of applied part (AP) and based on type of leakage current. The AP is a component of the medical equipment that comes into contact with the patient.

[0008] Some types of medical electrical equipment that come into contact with a patient are required to have a floating patient ground. This means that the equipment needs to ensure that the patient is not electrically connected to protective Earth via the equipment. For dialysis therapy, IEC60601-2-39:2018 applies to the basic safety and essential performance of medical electrical equipment for PD. It defines that PD equipment needs to be Class II BF (Body Floating). Class II BF require a floating patient ground and has a maximum allowed patient leakage current of 100 p A for NC and 500 p A for SFC. Here, NC (Normal Condition) refers to the situation when leakage current flows from the patient via the AP to Earth, and SFC (Single Fault Condition) refers to the situation when a component or isolation barrier breaks, causing the patient to be exposed to a potentially increased leakage current. Electrical equipment for EC blood therapy that is not connected to protective Earth needs to be Class II CF (Cardiac Floating). Class II CF requires a floating patient ground and has a maximum allowed patient leakage current of 10 p A for NC and 50 p A for SFC.

[0009] Dialysis therapy produces used ("spent") treatment fluid that needs to be handled. Often, spent treatment fluid is pumped from the patient along a flow path that extends to a drain, such as a toilet, bathtub or sink. The toilet, bathtub or sink may establish an Earth ground relative to the patient and the dialysis machine. Treatment fluid, and thus spent treatment fluid, is electrically conductive. The flow path may thus create a conductive path from the patient to the drain. If the patient comes into contact with mains power, for example by touching a short-circuited electric device, the patient may be subjected to an excessive electrical current.

[0010] It has been suggested to measure the leakage current in an electrically conductive fluid that flows on a fluid path from a patient to a drain and to actively break the flow when the leakage current exceeds a threshold, to thereby protect the patient from electrical shock. A rudimentary technique is disclosed in US9636454, in which the leakage current is monitored by capacitively measuring the field strength between an electrode on the outside of the drain tube and the fluid inside the drain tube. There is room for improvement.

[0011] Summary

[0012] It is an objective to at least partly overcome one or more limitations of the prior art.

[0013] One objective is to provide a technique capable of reliably monitoring the leakage current in a fluid flow path that is defined by a medical apparatus to extend between an individual and a drain.

[0014] Another objective is to provide such a technique for reliable detection when the individual is in physical contact with mains power.

[0015] Yet another objective is to provide a technique suitable for use in a medical device that is configured with a floating patient ground. One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by a fault detection device, a medical apparatus, a computer-implemented method and a computer-readable medium according to the independent claims, embodiments thereof being defined by the dependent claims.

[0016] By the present disclosure, a technique is proposed that enables robust and reliable monitoring of the leakage current in a fluid flow path between an individual and a drain. The proposed technique is particularly suited to detect a fault condition that occurs when the individual is direct contact with mains power and is applicable to medical apparatuses with floating patient ground. The proposed technique involves measuring an electrical property that is indicative of a voltage level at a sensing element in electrical contact with an electrically conductive fluid in the fluid flow path of the medical apparatus. After profound experimentation, the present Applicant has found that the fault condition is robustly indicated by the electrical property if measured both when a conducting wire path is established from the sensing element to a neutral power wire via a resistor device, and when this conductive wire path is broken.

[0017] Still other objectives and technical effects, as well as aspects, embodiments, features and advantages may appear from the following detailed description, from the attached claims as well as from the drawings.

[0018] Brief Description of the Drawings

[0019] FIG. 1A is a schematic representation of an example medical apparatus with a conductive fluid path between an individual and ground, FIG. IB shows the medical apparatus when the individual is in contact with mains power, and FIG. 1C is a schematic representation of the medical apparatus equipped with an example fault detection device.

[0020] FIG. 2 is a schematic circuit diagram of a combination of a fault detection device and a medical apparatus that is connected to an individual.

[0021] FIGS 3A-3B illustrate the circuit diagram in FIG. 2 for two different electrical paths established by the fault detection device in the absence of a fault condition.

[0022] FIGS 4A-4B illustrate the circuit diagram in FIG. 2 for two different electrical paths established by the fault detection device at the fault condition.

[0023] FIGS 5-9 are flow charts of example methods performed by a fault detection device in accordance with embodiments.

[0024] FIG. 10 is a schematic circuit diagram of a preparation unit in a fault detection device. FIGS 11A-1 IB are circuit diagrams of a combination of a fault detection device and a medical apparatus in accordance with detailed examples.

[0025] FIG. 12 is a block diagram of a control arrangement for a fault detection device.

[0026] Detailed Description of Example Embodiments

[0027] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the subject of the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements.

[0028] Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and / or operational aspects of any of the embodiments described and / or contemplated herein may be included in any of the other embodiments described and / or contemplated herein, and / or vice versa. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and / or vice versa, unless explicitly stated otherwise. As used herein, "at least one" shall mean "one or more" and these phrases are intended to be interchangeable. Accordingly, the terms "a" and / or "an" shall mean "at least one" or "one or more", even though the phrase "one or more" or "at least one" is also used herein. As used herein, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.

[0029] As used herein, the terms "multiple", "plural" and "plurality" are intended to imply provision of two or more elements. The term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0030] It will furthermore be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present disclosure.

[0031] Well-known functions or constructions may not be described in detail for brevity and / or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0032] Like reference signs refer to like elements throughout As used herein, "medical device" refers to any electrically controllable device that is intended to be used for medical purposes.

[0033] As used herein, "dialysis therapy" or "dialysis" refers to any therapy that replaces or supplements the renal function of a patient by use of a treatment fluid. Dialysis therapy includes, without limitation, PD therapy and EC blood therapy.

[0034] As used herein, "medical fluid" refers to any fluid that is consumed by a medical device. In the context of dialysis therapy, the medical fluid is denoted treatment fluid, which includes, without limitation, dialysis fluid for infusion into the peritoneal cavity during PD therapy, dialysis fluid for supply to a dialyzer during EC blood therapy, and replacement fluid and substitution fluid for infusion into blood during EC blood therapy.

[0035] Like reference signs refer to like elements throughout.

[0036] The present disclosure aims at minimizing the risk that an individual is exposed to potentially harmful leakage currents when the individual is fluidly connected to a medical apparatus on a fluid flow path that contains an electrically conductive fluid. In particular, the present disclosure addresses the risk that a harmful leakage current is generated when the individual is in contact with mains power and a conductive path is formed from the patient via the fluid flow path to a drain, which forms an electrical ground. The technique is particularly, but not exclusively, useful when the medical apparatus, and in particular the fluid flow path, is configured with a floating ground.

[0037] The present disclosure is applicable to any medical apparatus that is operable to define a fluid flow path, which contains an electrically conductive fluid and extends between an individual and a drain. In some embodiments, the medical apparatus is a dialysis system for PD therapy or EC blood therapy. As explained in the Background section, a dialysis system may be required to have a floating patient ground, where a dialysis system for PD may need to comply with Class II BF of the applicable IEC standard, and a dialysis system for EC blood dialysis may need to comply with Class II CF. It further non-limiting examples, the medical apparatus is an electrically operated machine for drainage of a fluid from a patient, for example a machine for surgical drain, or an electrically operated machine for liver support.

[0038] FIG. 1A is a schematic diagram of an individual or patient P, which is fluidly connected to a medical apparatus 10. The apparatus 10 comprises an electrically controlled machine system 11 and a fluid distribution arrangement ("fluid system") 20. The machine system 11 may include any number of separate machines. The machine system 11 may be operable to, via the fluid system 20, supply a medical fluid to the patient P, as well as obtain a drain fluid from the patient P and send the drain fluid to the drain 40. In some embodiments, the machine system 11 is further configured to generate the medical fluid that is supplied to the patient P, for example by mixing one or more concentrates with water. It is also conceivable that the machine system 11 is operable to only obtain drain fluid from the patient and send the drain fluid to the drain 40. The drain 40 is typically a fixed installation such as a sink, bathtub, toilet, floor drain, etc.

[0039] In the example of FIG. 1A, the fluid system 20 includes a machine portion 21, a patient portion 22 and a drain portion 23. The portions 21-23 jointly define a fluid flow path that extends between the machine 11, the patient P, and a drain 40. The machine system 11 may be operable to supply medical fluid to the patient P via the machine portion 21 and the patient portion 22. Further, the machine system 11 may be operable to dispose of drain fluid via the patient portion 22 and the drain portion 23, and optionally also via the machine portion 21 of the fluid system 20.

[0040] It may be noted that FIG. 1A is highly schematic. Each of the portions 21-23 is at least partly defined by fluid lines. The patient portion 22 may include more than one fluid line, for example one fluid line for conveying fluid to the patient and one fluid line for conveying fluid from the patient.

[0041] In one example, the apparatus 10 is a dialysis system for PD and the machine system 11 includes a so-called "cycler". As is well-known in the art, the cycler is provided with a disposable arrangement, commonly known as a "disposable set", which forms at least part of the fluid system 20 in FIG. 1A. The disposable set typically includes tubings, one or more bags and a fluid distribution cassette, which is configured for engagement with the cycler. The patient portion 22 is releasably connected to an implanted catheter in fluid communication with the peritoneal cavity of the patient P. The cycler performs the PD therapy, which may be implemented as daily treatment sessions, each comprising a number of fluid exchange cycles. The respective fluid exchange cycle may include a fill phase, a dwell phase and a drain phase, performed in sequence. In the fill phase, fresh treatment fluid is supplied to the peritoneal cavity via the patient portion 22. In the dwell phase, the dialysis fluid resides in peritoneal cavity. In the drain phase, spent treatment fluid is extracted from the peritoneal cavity via the patient portion 22 and sent to the drain 40 via the drain portion 23.

[0042] In another example, the apparatus 10 is a dialysis system for EC blood dialysis. In some installations, the machine system 11 comprises a so-called "monitor". Like in PD therapy, the monitor is provided with a disposable arrangement, which forms at least part of the fluid system 20 in FIG. 1A. The disposable arrangement typically includes a blood filtration unit ("dialyzer") and tubings, which are configured for engagement with the monitor. The patient portion 22 is connected to a vascular access on the patient P. To perform EC blood therapy, the monitor is operated to circulate blood from the patient via the dialyzer and back to the patient. There are different modalities of EC blood therapy, such as ultrafiltration, hemodialysis, hemofiltration, and hemodiafiltration. In some of these modalities, a treatment fluid is passed through the dialyzer and may also be directly infused into the blood of the patient. In all modalities, a drain fluid is passed to drain via the patient portion 22 and the drain portion 23.

[0043] It should be noted that the fluid system 20 need not be entirely defined by a disposable arrangement, but may include one or more durable fluid lines that are permanently integrated in the machine system 11. For example, such durable fluid lines may be included if the machine system 11 is configured to generate the medical fluid.

[0044] The machine system 11 is connected to receive power from a mains power source 30. The mains power source 30 may be a distribution apparatus that receives and distributes electrical current to the room where the machine system 11 is located. The distribution apparatus may, for example, be a distribution board, a circuit breaker panel, a fuse box, etc. In the illustrated example, the machine system 11 is configured to receive an alternating current from a mains power source 30 by connection to a live power line (L conductor) 31 and a neutral power line (N conductor) 32. As is well known, the L conductor supplies the alternating current and the N conductor receives and returns the alternating current to the main power source 30. In most electrical grid systems around the world, the N conductor is connected to protective earth (PE) at the point of supply. The machine system 11 comprises two power wires 12, 13, which are releasably connected to the conductors 31, 32 by an electrical connector 14. The electrical connector 14 may, for example, be a plug-socket arrangement.

[0045] A medical apparatus 11 with a floating patient ground does, by definition, not allow for the fluid system 20 to be connected to protective earth (PE). This is inherently achieved if the machine system 11 is configured with a floating ground. A machine system 11 with a floating ground does, by definition, not allow for connection to PE in the electrical connector 14. The machine system 11 in FIG. 1A is thus configured with both a floating ground and a floating patient ground.

[0046] FIG. IB shows a situation in which the patient P inadvertently comes into physical contact with mains power 50. This may, for example, happen if the patient is in contact with an electrical device that is suddenly short-circuited or otherwise provides a low-impedance connection to mains power. The electrical device may be any device that is connected to mains power and in physical contact with the patient, such as other medical equipment connected to the patient, a mobile phone, a computer, a lamp, an electrically adjusted bed or treatment chair, etc. The machine system 11 is typically configured to limit the passage of leakage currents in this situation, to protect the patient from electrical shock. However, the drain 40 is typically at electrical ground. If the fluid in the fluid system 20, between the patient P and the drain 40, is electrically conductive, a significant leakage current may be conducted by the fluid from the patient P to the drain 40, as indicated by a dotted arrow in FIG. IB. Thus, while fluid lines in the fluid system 20 may be made of electrically isolating material, electrical current may still be carried by the fluid inside the fluid lines.

[0047] In a non-limiting example, dialysis fluid for PD typically has a conductivity of about 14 mS / cm. In a tube with an inner diameter of 3 mm, the resistance of the dialysis fluid will be about 100 kQ per meter. If the extent of the fluid path from the patient to the drain 40 is 10 meters, there will be a leakage current of about 230 pA going to drain 40 from the patient P when connected to mains power of 230 V. It is currently believed that potentially harmful leakage currents may arise for fluids with an electrical conductivity above 1 mS / cm, depending on the dimensions of the fluid path between the patient P and the drain 40.

[0048] In FIG. 1C, the medical apparatus 10 is provided with a fault detection device (FDD) 60, which is configured to detect when the leakage current in the fluid system 20 is above a limit and take appropriate action to protect the patient P. The FDD 60 is connected to the power wires 12, 13 by wires 61, 62. The FDD 60 is also electrically connected to a sensing element 63, which is arranged to be in electrical contact with the fluid in the fluid system 20. The sensing element 63 is preferably in galvanic contact with the fluid. In some embodiments, the sensing element 63 is an electrode which is arranged inside a tube of the fluid system 20. In some embodiments, the sensing element 63 is included in a conductivity sensor, which may or may not be installed in the fluid system 20 for the separate purpose of providing conductivity data for the operation of the machine system 11. It is also conceivable that the sensing element 63 is electrically connected to the fluid via a capacitive coupling.

[0049] The sensing element 63 may be arranged anywhere in the fluid system 20, between the patient P and the drain 40. In the example of FIG. 1C, the sensing element 63 is arranged in the drain portion 23. An alternative location, in the patient portion 22, is indicated by dotted lines 63'.

[0050] In the illustrated example, the FDD 60 is connected by a signal line 64 to a separation device 65, which is operable to increase the impedance of the fluid flow path between the patient P and the drain 40 and thereby eliminate or at least significantly reduce the leakage current. In FIG. 1C, the FDD 60 has operated the separation device 65 to effectively eliminate the leakage current from the patient P to the drain 40 through the fluid in the fluid system 20. The separation device 65 may be configured to break the fluid flow path. This may be achieved in many different ways. For example, a pinch valve may be arranged to deform an electrically isolating tube portion to break the fluid flow path. In another example, an electrically isolating valve may be arranged in a fluid line to be selectively closed to break the fluid flow path. In another example, an injection device may be arranged to inject a low-conductivity fluid into the fluid system 20.

[0051] FIG. 2 is a schematic circuit diagram of an example FDD 60 installed in a medical apparatus, which in turn is fluidly connected to a patient P. To facilitate the following discussion, the machine system 11 and the fluid system 20 are represented by resistors. A junction JI corresponds to the sensing element 63. The line LI represents a conductive path formed by the fluid system 20 between the junction J 1 and the patient P. The resistance in LI is represented by a resistor Rl. The line L2 represents a conductive path formed by the fluid system 20 between the junction J 1 and a ground 40', which corresponds to the drain 40. The resistance in L2 is represented by a resistor R2. The circuit diagram in FIG. 2 further includes a line L5, which represents a conductive path from the fluid in the fluid system 20 through the machine system 11 to the L conductor 31. In FIG. 1C, the connection of the machine system 11 to the L conductor 31 is made via the power wire 12 and the electrical connector 14. The resistance in L5 is represented by a resistor R4.

[0052] The FDD 60 is connected between the sensing element 63 and the N conductor 32. In FIG. 1C, the connection to the N conductor 32 is made via the wire 61, the electrical connector 14 and the power wire 13. FIG. 2 includes a line L3 that represents a conducting wire path through the FDD 60 from JI to N. A switching unit ("switch") 160 is disposed in L3 and is operable to selectively open and close L3. The operation of the switch 160 is electrically controlled by a controller 161. In this context, the switch 160 is in a conducting state when closed and in an isolating state when open. The switch 160 may be a mechanical device such as a relay, or a semiconductor device such as a transistor-based switch. R3 is a resistor device ("measurement resistor"), which is connected in series with the switch 160. Thus, the FDD 60 is operable to establish a conducting wire path (L3) from the sensing element 63 (at JI) to the N conductor 32. It is to be noted that this conductive wire path (L3) extends only to the N conductor 32 and does not include the L conductor 31.

[0053] The FDD 60 comprises a measurement unit 162 which is arranged in a line L4 that extends between a first junction J31 on L3 on one side of the switch-resistor combination and a second junction J32 on L3 on the opposite side of the switch-resistor combination. The measurement unit 162 is configured to measure an electrical property between the junctions J31, J32 on L3. The electrical property is indicative of the voltage at the junction JI, i.e., at the sensing element 63. The electrical property may be a voltage or an electrical current. Thus, the measurement unit 162 may be a voltmeter or an ammeter. The output signal of the measurement unit 162 is received by a monitoring device 163, which is configured to evaluate the output signal for detection of a fault condition corresponding to an elevated leakage current. The monitoring device 163 may, for example, be implemented by a microcontroller or dedicated hardware, for example including an operational amplifier.

[0054] In the illustrated example, the FDD 60 further comprises a preparation device 164, which may be operated whenever the apparatus 10 is started to ensure that the FDD 60 is electrically connected to the N conductor 32. The preparation device 164 may be implemented when there is a risk that the polarity of the connection at the connector 14 (FIG. 1C) is changed between starts. The FDD 60 will not operate properly if the line L3 extends to the L conductor 31 instead of the N conductor 32. The preparation device 164 will be described below with reference to FIGS 9-10.

[0055] Some fundamentals of the FDD 60 will be described with reference to FIGS 3-4. The measurement unit 162 is assumed to generate an output signal representing voltage, Vout. FIGS 3A-3B show the circuit in FIG. 2 at a normal condition, when the patient is not connected to mains power 50. In FIG. 3A, the switch 160 is closed. In FIG. 3B, the switch 160 is open. FIGS 4A-4B show the circuit in FIG. 2 at a faulty condition, when the patient is connected to mains power 50. In FIG. 4A, the switch 160 is closed. In FIG. 4B, the switch 160 is open.

[0056] By comparing FIG. 3A and FIG. 4A, it is realized that Vout will increase in the closed state when the faulty condition happens, since R1 will them be added in parallel with R4. The combined resistance of R1 and R4 is lower than the resistance of R4, causing Vout to increase. Likewise, by comparing FIG. 3B and FIG. 4B, it is realized that Vout will increase in the open state when the faulty condition happens, for the same reason, at least when R2 has a finite value.

[0057] By comparing FIG. 3A and FIG. 3B, it is realized that Vout will increase in the normal condition when going from the closed state (FIG. 3A) to the open state (FIG. 3B), since R2 is no longer connected in parallel with R3. The resistance of R2 is higher than the combined resistance of R2 and R3, causing Vout to increase. Likewise, by comparing FIG. 4A and FIG. 4B, it is seen that Vout will increase in the faulty condition when going from the closed state (FIG. 4A) to the open state (FIG. 4B), for the same reason. However, as will be shown below, the change in Vout is smaller at the faulty condition, as a result of the addition of Rl. A further finding is that the change in Vout between closed and open states is much less dependent on R2 in the faulty condition than in the normal condition.

[0058] Based on the findings above, the present Applicant has identified different ways of detecting the faulty condition by use of the circuit in FIG. 2. Before describing different ways of detecting the faulty condition, the principles described above will be exemplified with reference to tests made for the circuit in FIG. 2. In these tests, R3 and R4 were set to 10 MO, R1 was set to 300 kQ, and R2 was set to different values from 100 kQ to infinity. As noted above, the dimensions of the drain portion 23 may differ between different installations, and it is desirable for the FDD 60 to be able to detect the faulty condition irrespective of the length of the drain portion 23.

[0059] The test results are listed in Table 1 and Table 2 below. Vout,c is the measured voltage in the closed state, Vout,o is the measured voltage in the open state, AVn is the change in measured voltage between closed and open states in the normal condition, and AVf is change in measured voltage between closed and open states in the faulty condition. The tables also includes RCn and RCf, which denote the relative change in the normal and faulty conditions, here given by the change in measured voltage divided by Vout,c.

[0060] Table 1 - Normal condition

[0061] Table 2 - Faulty condition

[0062] The above-described principles are reproduced by the test results in Tables 1-2. It is seen that if the resistances of R1 and R2 are approximately known, it is possible to define a threshold value that corresponds to a predefined limit for the leakage current in line L2. Thus, a faulty condition may be detected by comparing Vout,c and / or Vout,o to a respective threshold value.

[0063] However, as noted, the resistance of R2 may vary considerably between different installations. The resistance of R2 may also vary during operation of the medical apparatus 10, for example if the electrical conductivity of the fluid in the fluid system 20 changes over time.

[0064] The above-mentioned threshold value may be set for a worst-case scenario in terms of the resistance of R2. Assuming that the worst-case scenario is R2 = 100 kQ and looking at Table 2, the threshold value may be set to approximately 50 V, so that a faulty condition is detected whenever Vout,o and / or Vout,c exceeds this threshold value. However, looking at Table 1, it is seen that Vout,o and / or Vout,c will exceed 50 V for large resistance values of R2. Thus, a faulty condition may be erroneously detected when the fluid in the fluid system 20, between the sensing element 63 and the drain 40, has a high electrical resistance.

[0065] It may be noted that such erroneous detection may be obviated by also taking into account the difference between Vout,c and Vout,o. As seen in Table 2, AVf and RCf are relatively independent of R2, whereas AVn and RCn increases significantly with increasing resistance of R2.

[0066] FIG. 5 is a flow chart of an example method Ml of detecting an excessive leakage current in the fluid system 20 as a result of the patient P being in contact with mains power 50 (FIGS 1B-1C). The method Ml is based on the findings described with reference to FIGS 3-4 and Tables 1-2. The method Ml will be described with reference to FIGS 1-4 and is performed by the FDD 60. Some optional steps and sub-steps are indicated by dashed lines.

[0067] In step S10, a conducting wire path is established from the sensing element 63 to the neutral power wire 32 (and not to the live power wire 31) via the resistor device R3 in the FDD 60. In FIG. 2, the conducting wire path is established by the controller 161 setting the switch 60 in the closed (conducting) state, thereby closing L3. In step Si l, a first value indicative of the voltage level at the sensing element 63 is measured. In FIG. 2, the first value is measured by the measurement unit 162 and corresponds to the above-mentioned Vout,c. In step S13, the conducting wire path is broken. In FIG. 2, the conducting wire path is broken by the controller 161 setting the switch 160 in the open (isolating) state, thereby opening L3. In step S13, a second value indicative of the voltage level at the sensing element 63 is measured by the measurement unit 162 and corresponds to the above-mentioned Vout,o. In step S14, the first and second values are evaluated for detection of a fault condition that is indicative of the patient P being in physical contact with mains power 50. This corresponds to detecting that the electrical current (leakage current) in the fluid flow path 20 is above a predefined limit. In step S15, a dedicated action is taken upon detection of the fault condition to protect the patient P. Step S14 may be performed in different ways. In some embodiments, step S14 comprises a step S14a of evaluating the difference between the first and second values for detection of the fault condition. The difference may be an absolute difference or a relative difference. The relative difference may be given in relation to the first value or the second value. As seen from Tables 1-2, if R2 is known to be relatively large (for example, above about 2-3 MO), a fault condition may be detected whenever the absolute difference (cf. AVn, AVf) is below a threshold value. Likewise, if R2 is known to be relatively large (for example, at or above 1 MQ), a fault condition may be detected whenever the relative difference (cf. RCn, RCf) is below a threshold value. In some embodiments, step S14 comprises a step S14b of evaluating the magnitude of at least one of the first or second values for detection of the fault condition. This allows for robust detection of the fault condition for all reasonable values of R2. In the example of Tables 1-2, a fault condition may be detected if the absolute difference is below about 10 V and Vout,o (or Vout,c) is above 50 V. Even more robust detection may be achieved by using the relative difference. In the example of Tables 1-2, a fault condition may be detected if the relative difference is below about 5-10%, and Vout,o (or Vout,c) is above 50 V. Thus, steps S14a and S14b may be combined so that the FDD 60, by step S14, detects the fault condition when the difference between the first and second values is below a first threshold and the first and / or second value is above a second threshold.

[0068] It is to be understood that steps S10-S14 may be repeatedly performed for as long as the patient P is fluidly connected to the apparatus 10.

[0069] It is also to be noted that the first and second values may be represented as either voltage or electrical current.

[0070] It is realized that the first and second values, which are indicative of the voltage level at the sensing element 63, will also be affected by the supply voltage. To make the method Ml even more robust, it may include preparatory steps S1-S2. In step SI, the magnitude of the supply voltage of the mains power source 30 is obtained. This may be achieved in many different ways. In one example, the user is requested to enter a corresponding value, for example via a user interface on the FDD 60, the machine system 11 or the apparatus 10. Alternatively, it may be sufficient for the user to enter a current geographic location, such as a city or country. The FDD 60 may then use a lookup table to determine the supply voltage at the geographic location. In a variant, the FDD 60 may be configured to automatically determine the supply voltage, by directly measuring the supply voltage between the conductors 31, 32 (FIGS 1A-1C) or by measuring the frequency of the supply voltage. The FDD 60 may then use a look-up table to determine the supply voltage based on the frequency. In step S2, one or more threshold values for use in step S14 is determined or set based on the supply voltage. The FDD 60 may use a predefined look-up table or function to set the threshold value(s).

[0071] Different actions may be taken in step S 15. In a first example, represented by step S15a, the FDD 60 causes an alarm to be generated, for example on a user interface of the apparatus 10 or the machine system 11. In a second example, represented by step S15b, the FDD 60 causes the impedance of the fluid system 20 to be increased, for example by operation of the separation device 65 (FIG. 1C). Of course, steps S15a, SI 5b may be combined. In a further example, represented by step S15c, the conducting wire path between the sensing element 63 and the neutral power wire 32 is broken, by setting the switch 160 to the open state. Step SI 5c may be included to minimize the risk that the patient P is exposed to a leakage current that passes via LI and L3 to N.

[0072] FIG. 6 is an example method M2 that may be performed as part of step S15 in FIG. 5 when the separation device 65 is arranged intermediate the sensing element 63 and the patient P, for example as exemplified in FIG. 1C. In step S20, the separation device 65 is operated to increase the impedance of the fluid system 20, for example by breaking the continuity of the fluid flow path. In step S21, it is evaluated whether the fault condition persists or not, by performing steps S10-S14. If the fault condition persists, the elevated leakage current detected by the FDD 60 originates from the machine system 11. Step S22 is therefore performed to stop the apparatus 10 from receiving power from the mains power source 30, for example by activating an emergency or safety relay (not shown) to break the power supply to the apparatus 10. If the fault condition is found to cease in step S21, the leakage current originates from the patient P, and step S23 may be performed to generate an alarm, and optionally stop the operation of the apparatus 10.

[0073] FIG. 7 is an example method M3 that may be performed as part of step S15 in FIG. 5 when the sensing element 63 is arranged intermediate the separation device 65 and the patient P, for example at location 63' in FIG. 1C. In step S30, the separation device 65 is operated to increase the impedance of the fluid system 20, for example by breaking the continuity of the fluid flow path. In step S31, it is evaluated whether the fault condition persists or not, by performing steps S10-S14. If the fault condition ceases, the elevated leakage current detected by the FDD 60 originates from the machine system 11. Step S32 is therefore performed to stop the apparatus from receiving power from the mains power source 30, by analogy with step S22. If the fault condition is found to persist in step S31, the leakage current originates from the patient P and step S33 may be performed to generate an alarm. In the illustrated example, the apparatus 10 is allowed to continue its operation for a test period while step S36 is performed to evaluate whether the fault condition ceases. If the fault condition ceases during the test period, this means that the patient P is no longer in contact with mains power. Step S37 is therefore performed to operate the separation device 65 to re-open the fluid flow path. Also, the alarm generated by step S33 may be terminated. On the other hand, if the fault condition does not cease before the end of the test period, step S34 causes the method M3 to proceed to step S35, in which the operation of the apparatus 10 is stopped, and optionally the switch 160 is opened (cf. step S15c). The use of the test period allows for the instinctive reaction of the patient P to try to get out of contact with mains power. Thus, if the fault condition persists for a time period after step S30 and then ceases, it is concluded that the patient has let go of the mains power and treatment may continue. The method M3 will ensure continuity of the medical treatment. The test period may be set to avoid harming the patient P. For example, the test period may be less than 1-10 ms.

[0074] FIG. 8 is an example method M4 that may be performed by the FDD 60 at startup of the apparatus 10 to check that the leakage current through the machine system 11 is acceptable. During the method M4, the apparatus is configured without a conductive path between the sensing element 63 and the patient P. For example, the patient P may be disconnected from the fluid system 20 or otherwise electrically isolated from the sensing element 63, for example by the separation device 65 being operated to break the fluid flow in the patient portion 22 (FIG. 1C). In step S40, the conducting wire path between the sensing element 63 and N is established. In step S41, a third value indicative of the voltage level at the sensing element 63 is measured. With reference to FIG. 2, the third value represents the electrical current that passes from L to N on L5 and L3. In step S42, the third value is evaluated for detection of an elevated internal leakage current through the machine system 11. Step S42 may involve comparing the third value to a predefined threshold. If an elevated internal leakage current is detected, step S43 may be performed to take dedicated action, for example alerting the user and / or preventing further operation of the apparatus 10.

[0075] FIG. 9 is an example method M5 of operating the FDD 60 during a preparatory phase. The method M5 may utilize the preparation device 164 in FIG. 2. Reverting to FIG. 1C, it is seen that the FDD 60 is connected to the power lines 31, 32 via the wires 61, 62. Depending on the connector 14, it is possible that either of the wires 61, 62 is connected to the neutral power line 32. For example, if the connector 14 defines a plugsocket arrangement, the pins on the plug may interface with the holes on the socket in two orientations. As noted above, for proper operation, L3 in the FDD 60 should extend to N. This is ensured by the method M5.

[0076] The method M5 will be described with reference to an example preparation device 164 shown in FIG. 10. The device 164 comprises a switch arrangement 165 which is connected to a terminal end L3a of the line L3 and to terminal ends of the wires 61, 62. The switch arrangement 164 is configured to be electrically switchable between a first state, in which L3 is galvanically connected to wire 61 via a first pole 165a, and a second state, in which L3a is galvanically connected the wire 62 via a second pole 165b. The switch arrangement 165 may be a relay or a semiconductor switch. The switch arrangement 165 is operated by a controller 166. In the illustrated example, protective capacitors (Y-capacitors) Cl, C2 are additionally arranged in the respective wire 61, 62 to prevent high leakage currents in the event that the resistor device R3 is short- circuited.

[0077] The method M5 is performed while the fluid system 20 contains the electrically conductive fluid, which may or may not be in electrical contact with the ground 40' formed by the drain 40. During the method M5, the patient P may be disconnected from the fluid system 20 or electrically isolated from the machine system 11, for example by the separation device 65 being operated to break the fluid flow in the patient portion 22 (FIG. 1C). In step S50, a first test path is established to extend from the sensing element 63 via the resistor device R3 to a first wire among the neutral and live power wires 31, 32. In FIG. 10, step S50 may set the switching arrangement 165 in the first state. In step S51, a fourth value indicative of the voltage level at the sensing element 63 is measured by the measurement unit 162 (FIG. 2). In step S52, a second test path is established to extend from the sensing element 63 via the resistor device R3 to a second wire among the neutral and live power wires 31, 32. In FIG. 10, step S52 may set the switching arrangement 165 in the second state. In step S53, a fifth value indicative of the voltage level at the sensing element 63 is measured by the measurement unit 162 (FIG. 2). In step S54, the conducting wire path for use in the method Ml is defined based on the fourth and fifth values, by setting the switch arrangement 165 in either the first state or the second state. Typically, the voltage at the sensing element 63 will be lower when L3 is connected to N compared L. When L3 is connected to N, some leakage current will be diverted from L3 to a metal chassis that is capacitively coupled to N, as shown in FIGS 11A-11B (below). Thus, step S54 may involve determining the lowest value among the fourth and fifth values, and set the switch arrangement 165 in the state that yielded the lowest value. Thus, the switch arrangement 165 will be switched to one of the first and second states and stay this way until the machine system 11 is powered off or otherwise loses power.

[0078] FIG. 11 A shows a more detailed example of an apparatus 10 that is connected to a patient P and equipped with an FDD. The extent of the machine system 11 is approximately indicated by dashed lines. The machine system 11 comprises a power supply unit (PSU) 111, which is configured to receive an alternating current from a mains power source (30 in FIGS 1A-1C) on power wires 12, 13 and provide a DC voltage, for example 24 V, between first and second internal power distribution lines 112, 113. The lines 112, 113 meet at a junction J2, which corresponds to J2 in FIG. 2. All internal components between the junction J2 and the PSU 111 are represented by a resistor R4'. The path from J2 to the power wire 12 corresponds to L5 in FIG. 2. A line L2 extends from J2 to the ground 40' formed by the drain 40. The sensing element 63 is not shown in FIG. 11A but is located at a junction JI. A line LI extends from the patient P to a junction JI' on line L2. The junction JI' is at the same potential as the junction JI, since there is no resistance between JI and JI' in FIG. 11A. Like in FIG. 2, the resistance between the patient P and the sensing element (junction JI) is represented by a resistor R1 and the resistance between the sensing element (junction JI) and the ground 40' is represented by a resistor R2. A line L3 extends from JI to the switch arrangement 165 of the above-mentioned preparation device (164 in FIG. 10). The switch arrangement 165 is connected to the wires 61, 62 via optional protective capacitors Cl, C2. The controller 166 for the switch arrangement 165 is not shown in FIG. 11A. In line L3, a switch 160 is connected in series with a measurement resistor R3, and a measurement unit 162 is connected by a line L4 to measure voltage over or electrical current through the combination of the switch 160 and resistor R3. The line L4 is connected to L3 at junctions J31, J32. In FIG. 11A, the switch 160 is a transistor. The switching of the transistor 160 is controlled by a controller 161. The controller 161 is powered via a line 118 that extends to a junction J4 on the internal power distribution line 112. The controller 161 may include a switch driver, a pulse generator and control electronics, as is well-known to the skilled person. In the illustrated example, a line 113 is connected to L3 at a junction J33 upstream of the switch 160. The line 113 defines a leakage current path which extends to a metal chassis or frame 116 via an optional protective capacitor 115. The metal chassis 116 is capacitively coupled to PE or N, as indicated by a capacitance 117 and dashed lines 113', 113". As noted above, N is typically connected to PE at the point of supply. Leakage current to PE / N via the metal chassis 116 is inevitable in the apparatus 10 and is the reason why it is possible to detect if wire 61 or wire 62 is connected to N by the method M5 in FIG. 9.

[0079] The configuration in FIG. 11 A may be suitable when the separation device 65, as shown, is located intermediate the sensing element (junction JI) and the patient P. FIG. 1 IB shows a variant, in which the sensing element 63 (junction JI) is located in LI between the separation device 65 and the patient P. To block a potential leakage path for electrical current, a DC / DC isolator 166 is arranged in line 118, for example intermediate the controller 161 and the junction J4, as shown in FIG. 11B. The DC / DC isolator 166 is arranged to provide galvanic isolation between L3 and line 112 so as to effectively eliminate the risk that a leakage current flows through the patient even if the separation device 65 has been operated to break the continuity of the fluid flow in the fluid system.

[0080] FIG. 12 is a block diagram of a computer device 70, which may implement the FDD 60 or part thereof by a combination of software and hardware circuitry, or exclusively by specific hardware circuitry. In FIG. 12, the computer device 70 comprises processor circuitry 71, which may be or include a central processing unit (CPU), graphics processing unit (GPU), microcontroller, microprocessor, ASIC, FPGA, or any other specific or general processing device. The computer device 70 further comprises computer memory 72 and a signal interface 73 for receiving input signals, for example the output signal of the measurement unit 162. The interface 73 may include conventional hardware for wired or wireless communication. The memory 72 may comprise one or more of a buffer, flash memory, hard drive, removable medium, volatile memory, non-volatile memory, random access memory (RAM), or another suitable data storage device. Such a memory 72 is considered a non-transitory computer-readable medium. A control program 72A comprising computer instructions is stored in the memory 72 and executed by the processor circuitry 71 to implement logic that may perform any method, procedure, function, operation, or step described herein. The control program 72 A may be supplied to the computer device 70 on a computer-readable medium 74, which may be a tangible (non-transitory) product (for example, magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. As indicated in FIG. 12, the memory 72 may also store control data 72B for use by the processor circuitry 71, such as the above-mentioned thresholds, lookup table(s), etc.

[0081] The foregoing examples of the proposed fault detection technique are given for a medical apparatus with a floating patient ground. In principle, the proposed technique is equally applicable to a medical apparatus that is configured for connection to protective earth (PE), whether or not the medical apparatus has a floating patient ground or not. However, for this type medical apparatus, there may be simpler ways of detecting that the patient is in physical contact with mains power.

[0082] While the subject of the present disclosure has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the subject of the present disclosure is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0083] Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the parti- cular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

[0084] In the following, clauses are recited to summarize some aspects and embodiments as disclosed in the foregoing.

[0085] Cl. A fault detection device for a medical apparatus (10) that is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), wherein the fault detection device is configured to be connected between the neutral power wire (32) and a sensing element (63) in electrical contact with the electrically conductive fluid in the fluid flow path (20), and wherein the fault detection device is configured to: measure a first value indicative of a voltage level at the sensing element (63) while establishing a conducting wire path from the sensing element (63) to the neutral power wire (32) via a resistor device (R3) in the fault detection device; measure a second value indicative of the voltage level at the sensing element (63) while breaking the conducting wire path; evaluate the first and second values for detection of a fault condition that is indicative of the individual (P) being in physical contact with mains power (50); and take a dedicated action upon detection of the fault condition.

[0086] C2. The device of Cl, wherein the fluid flow path (20) is arranged to be nongrounded when the medical apparatus (10) is connected to the mains power source (30).

[0087] C3. The device of Cl or C2, wherein, at the fault condition, an electrical current in the fluid flow path (20) is above a predefined limit.

[0088] C4. The device of any preceding clause, which is configured to detect the fault condition based on a difference between first and second values.

[0089] C5. The device of C4, which is configured to detect the fault condition when the difference is below a first threshold and the first and / or second value is above a second threshold.

[0090] C6. The device of C5, further comprising: determining a supply voltage of the main power source (50) and setting the first and / or second threshold based on the supply voltage.

[0091] C7. The device of any preceding clause, which comprises a switching unit (160), which is operable between a conducting state and an isolating state and is connected in series with the resistor device (R3) in the conducting wire path, and a measurement unit (162) which is connected to measure an electrical property for the combination of the switching unit (160) and the resistor device (R3). C8. The device of C7, which is configured to operate the measurement unit (162) to measure the first and second values while operating the switching unit (160) in the conducting state and in the isolating state, respectively.

[0092] C9. The device of C7 or C8, wherein the electrical property is an electrical current or a voltage.

[0093] CIO. The device of any preceding clause, wherein the dedicated action comprises: causing a separation device (65) to increase an electrical impedance in the fluid flow path (20) between the individual (P) and the drain (40).

[0094] Cl 1. The device of CIO, wherein the dedicated action further comprises breaking the conducting wire path.

[0095] C12. The device of CIO or Cl 1, wherein the fluid flow path (20) comprises a first portion (22) that is configured to extend from the medical apparatus (10) to the individual (P), and a second portion (23) that is configured to extend from the medical apparatus (10) to the drain (40), and wherein the separation device (65) is arranged in the first portion (22) or the second portion (23).

[0096] C13. The device of C12, wherein the separation device (65) is arranged in the first portion (22), and the sensing element (63) is arranged in the first portion (22) intermediate the separation device (65) and the individual (P).

[0097] C14. The device of C13, which is configured to, if the fault condition ceases when the separation device (65) is caused to break the fluid flow path (20), cause the medical apparatus (10) to stop receiving the alternating current from the mains power source (30).

[0098] C15. The device of C13 or C14, which is configured to, if the fault condition persists for a time period after the separation device (65) is caused to break the fluid flow path (20) and then ceases, cause the separation device (65) to open the fluid flow path (20).

[0099] C16. The device of C12, wherein the separation device (65) is arranged in the first portion (22) intermediate the sensing element (63) and the individual (P).

[0100] C17. The device of C16, which is configured to, if the fault condition persists when the separation device is caused to break the fluid flow path (20), cause the medical apparatus to stop receiving the alternating current from the mains power source (30).

[0101] Cl 8. The device of any preceding clause, which is further configured to, when the medical apparatus is configured without a conductive path between the sensing element (63) and the patient (P), measure a third value indicative of the voltage level at the sensing element (63) while establishing the conducting wire path, evaluate the third value for detection of a further fault condition, and take further dedicated action upon detecting the further fault condition.

[0102] Cl 9. The device of any preceding clause, which is further configured to perform a preparatory phase for defining the conductive wire path, wherein the preparatory phase comprises: measuring a fourth value indicative of the voltage level at the sensing element (63) while establishing a first test path from the sensing element (63) via the resistor device (R3) to a first wire among the neutral and live power wires (31, 32), measuring a fifth value indicative of the voltage level at the sensing element (63) while establishing a second test path from the sensing element (63) via the resistor device (R3) to a second wire among the neutral and live power wires (31, 32), and defining the conducting wire path based on the third and fourth values.

[0103] C20. The device of Cl 9, which is configured to use the first test path as the conducting wire path if the fourth value is smaller than the fifth value, and use the second test path as the conducting wire path if the fifth value is smaller than the fourth value.

[0104] C21. The device of C19 or C20, which comprises a switch arrangement (165) for selectively establishing the first test path and the second test path, respectively, wherein the fault detection device is configured to define the conducting wire path by operating the switch arrangement (165) to establish the first test path and the second test path, respectively.

[0105] C22. The device of C21, wherein the switch arrangement (165) is located in the conducting wire path.

[0106] C23. A medical apparatus that is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), and wherein the medical apparatus comprises a fault detection device according to any one of C1-C22.

[0107] C24. A computer-implemented method of monitoring a medical apparatus for fault detection, wherein the medical apparatus is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), and wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), said method comprising: measuring (SI 1) a first value, which is indicative of a voltage level at a sensing element (63) in electrical contact with the electrically conductive fluid in the fluid flow path (20), while establishing (S10) a conducting wire path from the sensing element (63) to the neutral power wire (32) via a resistor device (R3); measuring (S13) a second value, which is indicative of the voltage level at the sensing element (63), while breaking (S12) the conducting wire path; evaluating (S14) the first and second values for detecting a fault condition that is indicative of the individual (P) being in physical contact with mains power (50); and taking (SI 5) a dedicated action upon detecting the fault condition.

[0108] C25. A computer-readable medium comprising instructions (72A) which when executed by processor circuitry (71) causes the processor circuitry (71) to perform the method of C24.

Claims

1. 23CLAIMS1. A fault detection device for a medical apparatus (10) that is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), wherein the fault detection device is configured to be connected between the neutral power wire (32) and a sensing element (63) in electrical contact with the electrically conductive fluid in the fluid flow path (20), and wherein the fault detection device is configured to: measure a first value indicative of a voltage level at the sensing element (63) while establishing a conducting wire path from the sensing element (63) to the neutral power wire (32) via a resistor device (R3) in the fault detection device; measure a second value indicative of the voltage level at the sensing element (63) while breaking the conducting wire path; evaluate the first and second values for detection of a fault condition that is indicative of the individual (P) being in physical contact with mains power (50); and take a dedicated action upon detection of the fault condition.

2. The device of claim 1, wherein the fluid flow path (20) is arranged to be nongrounded when the medical apparatus (10) is connected to the mains power source (30).

3. The device of claim 1 or 2, wherein, at the fault condition, an electrical current in the fluid flow path (20) is above a predefined limit.

4. The device of any preceding claim, which is configured to detect the fault condition based on a difference between first and second values.

5. The device of claim 4, which is configured to detect the fault condition when the difference is below a first threshold and the first and / or second value is above a second threshold.

6. The device of claim 5, further comprising: determining a supply voltage of the main power source (50) and setting the first and / or second threshold based on the supply voltage.

7. The device of any preceding claim, which comprises a switching unit (160), which is operable between a conducting state and an isolating state and is connected in series with the resistor device (R3) in the conducting wire path, and a measurement unit (162) which is connected to measure an electrical property for the combination of the switching unit (160) and the resistor device (R3).

8. The device of claim 7, which is configured to operate the measurement unit (162) to measure the first and second values while operating the switching unit (160) in the conducting state and in the isolating state, respectively.

9. The device of claim 7 or 8, wherein the electrical property is an electrical current or a voltage.

10. The device of any preceding claim, wherein the dedicated action comprises: causing a separation device (65) to increase an electrical impedance in the fluid flow path (20) between the individual (P) and the drain (40).

11. The device of claim 10, wherein the dedicated action further comprises breaking the conducting wire path.

12. The device of claim 10 or 11, wherein the fluid flow path (20) comprises a first portion (22) that is configured to extend from the medical apparatus (10) to the individual (P), and a second portion (23) that is configured to extend from the medical apparatus (10) to the drain (40), and wherein the separation device (65) is arranged in the first portion (22) or the second portion (23).

13. The device of claims 12, wherein the separation device (65) is arranged in the first portion (22), and the sensing element (63) is arranged in the first portion (22) intermediate the separation device (65) and the individual (P).

14. The device of claim 13, which is configured to, if the fault condition ceases when the separation device (65) is caused to break the fluid flow path (20), cause the medical apparatus (10) to stop receiving the alternating current from the mains power source (30).

15. The device of claim 13 or 14, which is configured to, if the fault condition persists for a time period after the separation device (65) is caused to break the fluidflow path (20) and then ceases, cause the separation device (65) to open the fluid flow path (20).

16. The device of claim 12, wherein the separation device (65) is arranged in the first portion (22) intermediate the sensing element (63) and the individual (P).

17. The device of claim 16, which is configured to, if the fault condition persists when the separation device is caused to break the fluid flow path (20), cause the medical apparatus to stop receiving the alternating current from the mains power source (30).

18. The device of any preceding claim, which is further configured to, when the medical apparatus is configured without a conductive path between the sensing element (63) and the patient (P), measure a third value indicative of the voltage level at the sensing element (63) while establishing the conducting wire path, evaluate the third value for detection of a further fault condition, and take further dedicated action upon detecting the further fault condition.

19. The device of any preceding claim, which is further configured to perform a preparatory phase for defining the conductive wire path, wherein the preparatory phase comprises: measuring a fourth value indicative of the voltage level at the sensing element (63) while establishing a first test path from the sensing element (63) via the resistor device (R3) to a first wire among the neutral and live power wires (31, 32), measuring a fifth value indicative of the voltage level at the sensing element (63) while establishing a second test path from the sensing element (63) via the resistor device (R3) to a second wire among the neutral and live power wires (31, 32), and defining the conducting wire path based on the third and fourth values.

20. The device of claim 19, which is configured to use the first test path as the conducting wire path if the fourth value is smaller than the fifth value, and use the second test path as the conducting wire path if the fifth value is smaller than the fourth value.

21. The device of claim 19 or 20, which comprises a switch arrangement (165) for selectively establishing the first test path and the second test path, respectively, wherein the fault detection device is configured to define the conducting wire path by operating26 the switch arrangement (165) to establish the first test path and the second test path, respectively.

22. The device of claim 21, wherein the switch arrangement (165) is located in the conducting wire path.

23. A medical apparatus that is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), and wherein the medical apparatus comprises a fault detection device according to any one of claims 1-22.

24. A computer-implemented method of monitoring a medical apparatus for fault detection, wherein the medical apparatus is operable to define a fluid flow path (20), which contains an electrically conductive fluid and extends between an individual (P) and a drain (40), and wherein the medical apparatus (10) is configured to receive an alternating current from a mains power source (30) by connection to a live power wire (31) and a neutral power wire (32), said method comprising: measuring (SI 1) a first value, which is indicative of a voltage level at a sensing element (63) in electrical contact with the electrically conductive fluid in the fluid flow path (20), while establishing (S10) a conducting wire path from the sensing element (63) to the neutral power wire (32) via a resistor device (R3); measuring (S13) a second value, which is indicative of the voltage level at the sensing element (63), while breaking (S12) the conducting wire path; evaluating (S14) the first and second values for detecting a fault condition that is indicative of the individual (P) being in physical contact with mains power (50); and taking (S15) a dedicated action upon detecting the fault condition.

25. A computer-readable medium comprising instructions (72A) which when executed by processor circuitry (71) causes the processor circuitry (71) to perform the method of claim 24.

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