AU2011265560B2

AU2011265560B2 - Electrical fault detection

Info

Publication number: AU2011265560B2
Application number: AU2011265560A
Authority: AU
Inventors: Paul David Canvin; Andrew David Plumridge
Original assignee: ALTERNATIVE IDEAS Pty Ltd
Current assignee: ALTERNATIVE IDEAS Pty Ltd
Priority date: 2010-12-24
Filing date: 2011-12-23
Publication date: 2016-09-01
Anticipated expiration: 2031-12-23
Also published as: AU2011265560A1

Abstract

A device for detecting an electrical fault in an electrical circuit, wherein the device is in electrical communication across two points of an electrical conductor of the electrical circuit, wherein the device includes a detection circuit to detect a voltage differential, 5 across the two points of the electrical conductor, which exceeds a voltage differential threshold for a threshold period of time, and to output the detection to a relay to prevent current being supplied through the electrical conductor in the event of a successful detection. o 0f ww o ww CD w

Description

ELECTRICAL FAULT DETECTION

Technical Field

The present invention relates to a device for detecting an electrical fault in an electrical circuit.

Background A common problem that occurs in electrical systems is that an electrical fault occurs. The electrical fault may be caused by a number of factors, such as a short circuit, however other faults are also possible. In some electrical systems, the electrical fault can result in damage to equipment.

One common method to handle an electrical fault may be to use a fuse, wherein the fuse is configured to melt when too much current passes therethrough. However, in some electrical systems where in normal and safe operation there is a large amount of current passing through an electrical medium of a circuit for a short period of time, a fuse may not necessarily be appropriate due to the fuse melting in normal (i.e. non-fault condition) operation of the electrical circuit. Such types of electrical systems which show this type of operating characteristic include starter motors where actuation thereof causes a large amount of current to pass through a battery cable for a short period of time until the motor begins operating. It will be appreciated that whilst this example is given to provide the currently discussed problem in context, it will be appreciated that this problem is not specifically limited to systems that include a starter motor.

For some systems an electrical fault can have disastrous consequences. For example, on equipment with battery systems, large amounts of current can produce thermal heating of cables and can cause ignition of the insulation. Depending on circumstances, this may cause machinery fires or other damage.

There is therefore a need to a device for detecting an electrical fault which overcomes or at least alleviates one or more of the above-mentioned problems or at least provides a commercial alternative.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Summary of Invention

In one aspect there is provided a device for detecting an electrical fault in an electrical circuit, wherein the device is in electrical communication across two points of a single electrical conductor of the electrical circuit, the two points of the single electrical conductor being spaced apart along the electrical conductor and there being no other electrical components connected between the two points of the single electrical conductor, wherein the device includes a detection circuit to detect a voltage differential, across the two points of the single electrical conductor, which exceeds a voltage differential threshold for a threshold period of time, and to output the detection to a relay to prevent current being supplied through the single electrical conductor in the event of a successful detection.

In particular embodiments, the device includes the relay.

In certain embodiments, the device includes a relay power supply to supply electrical power to the relay when the current is prevented from flowing through the single electrical conductor.

In particular embodiments, the voltage differential threshold is proportional to a supply voltage of the electrical circuit.

In certain embodiments, the proportional relationship between the voltage differential threshold and the supply voltage is selectively adjustable via a voltage differential threshold adjustment means.

In particular embodiments, one or more resistance properties of the electrical cable are obtained to adjust the voltage differential threshold.

In certain embodiments, the one or more resistance properties are input via an input means.

In particular embodiments, the one or more resistance properties include at least one of: a resistance of the single electrical conductor; a gauge of the single electrical conductor; and a length between the two points of the single electrical conductor.

In certain embodiments, the device includes a resistance detection circuit to detect the resistance of the single electrical conductor.

In particular embodiments, the device dynamically adjusts the threshold voltage in response to a detected mode of operation of the load.

In certain embodiments, the threshold period of time is selectively adjustable via a temporal threshold adjustment means.

In particular embodiments, the detection circuit is configured to detect if the device is disconnected from one of the two points of the single electrical conductor, wherein in response to detecting that the device is disconnected from one of the two points of the single electrical conductor, the detection circuitry actuates the relay to prevent current passing through the single electrical conductor.

In certain embodiments, the detection circuit includes a device power supply to provide electrical power to the device in the event that insufficient electrical power is provided from the single electrical conductor due to the operation of the load.

In particular embodiments, the device includes an inactivity temporal threshold input means to set an inactivity temporal threshold, wherein the device includes an input port to receive a feedback signal from the load indicative of the activity of the load, wherein in the event that the feedback signal is indicative that the load has been inactive for a period of time which equals or exceeds the inactivity temporal threshold, the relay is actuated to prevent current passing through the single electrical conductor.

In certain embodiments, the detection circuit is a processing system.

In particular embodiments, the processing system includes a processor in electrical communication with memory, an input means and an output means.

In certain embodiments, the processor records measurements detected from the two points of the single electrical conductor in a log in the memory.

In particular embodiments, the processor compares measurements detected from the two points of the single electrical conductor against the log, wherein in the event the event of a discrepancy between the measurements and the log which exceeds a comparison threshold, the device presents a warning via the output means.

In certain embodiments, the processing system includes a communication interface to allow communication of data with an external device.

In particular embodiments, the processor presents a detected current flowing through the single electrical conductor via the output means.

Other embodiments will be described throughout the description of the example embodiments.

Brief Description of the Figures

Example embodiments should become apparent from the following description, which is given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures.

Figure 1A illustrates a block diagram representing an example of a device for detecting an electrical fault;

Figure IB illustrates a block diagram representing an example of another device for detecting an electrical fault;

Figure 2 is a graph illustrating current measurement and voltage measurements of battery and starter terminals during normal operation of an electrical circuit;

Figure 3 is a graph illustrating current measurement and voltage measurements of battery and starter terminals an electrical circuit having an electrical fault;

Figure 4 is a detailed electrical schematic of an example of a device for detecting an electrical fault; and

Figure 5 is a functional block diagram illustrating a processing system suitable for use in the device.

Detailed Description of Preferred Embodiments

The following modes, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments. In the figures, incorporated to illustrate features of an example embodiment, like reference numerals are used to identify like parts throughout the figures.

Referring to Figure 1A, there is shown a block diagram representing an example of a device 10 for detecting an electronic fault in an electrical circuit. In particular, the device is in electrical communication across two points 100, 110 of an electrical conductor 120 of the electrical circuit 130. The electrical conductor 120 is generally an electrical cable. Generally, there are no electrical components in electrical communication between the two points of the electrical conductor 120. The device 10 includes a detection circuit 20 having input from two points 100, 110 of an electrical cable, and an output 21. Optionally, the output is in electrical communication with a relay 30. The detection circuit 20 is configured to detect a voltage differential, across the two points of the electrical cable 120, which exceeds a voltage differential threshold for a threshold period of time. A relay 30 can be electrically actuated by the detection unit 20, in the event that the detected voltage differential exceeds the voltage differential threshold for the threshold period of time, to restrict current being supplied through the electrical circuit 130.

As shown in Figure 1A, the relay 30 is part of the device 10. However, as shown in Figure IB, it is possible that the device is in electrical communication with the relay 30 which is separate to the device 10.

As will be appreciated from the above arrangement of the device 10, the device 10 detects the voltage differential caused by the resistance of the monitored electrical cable. For example, referring to Figures 2 and 3, there is shown the voltage differential between two points 100, 110 of a monitored electrical cable 120 of an electrical circuit 130, wherein in Figure 2 the voltage differential between the two points 100, 110 over the time frame depicted is less than the voltage differential threshold (Vj). However, as shown in Figure 3, the voltage differential between the two points 100, 110 exceeds the voltage differential threshold (VT), wherein the voltage differential exceeding the threshold voltage is indicative of an electrical fault such as an overcurrent situation.

By detecting the voltage differential over the cable, a spike in current which exceeds the defined period of time can be identified, such that the relay 30 can be tripped, thereby reducing the risk of damage to the electrical circuit 130, and associated equipment, from the high amount of current flowing therethrough. It will be appreciated that the device 10 uses the electrical cable 120 of the electrical circuit 130 as a form of a current shunt in order to detect a situation where the current passing through the circuit 130 for a period of time exceeds the defined thresholds.

The device 10 is configured to detect a number of faults of the electrical circuit 130. In particular, the device 10 is configured to detect at least one of an overload condition, a short circuit, one or more disconnected cables of the circuit, and an arcing fault where the short circuit load is intermittent.

Preferably, the detection circuit 20 compensates for the drop in supply voltage caused by a load on the battery supply. In particular, the voltage differential threshold is a variable value which is proportional to a supply voltage B of the electrical circuit 130. Therefore, as voltage differential across the electrical cable varies according to the variable load L that is electrically connected to the electrical circuit 130, the voltage differential threshold can proportionally adjust accordingly. As will be appreciated, the detection circuit effectively compares the voltage drop over the two points 100, 110 of the electrical cable 120 against a shifting reference voltage.

In most situations, an electrical resistance between the two points 100, 110 of the electrical cable 120 may vary from one electrical circuit to the next. Therefore, when the device 10 is installed for a particular electrical circuit, specific thresholds of the device may require configuration for the specific operation of the electrical system.

In particular, the device 10 may include one or more inputs 40 to selectively adjust particular thresholds which are used by the device 10 for monitoring the operation of the electrical circuit.

Specifically, a voltage differential threshold adjustment means may allow a user to selectively adjust the proportional relationship between the voltage differential threshold and the voltage differential sensed. In particular embodiments, for example, the detection circuit 20 is configured to include significant sensitivity to detect the difference between a normally loaded starter motor and a starter motor stalled on a locked engine. In specific arrangements, the voltage differential threshold adjustment means may be adjusted in order to detect a voltage differential of lmV across the monitored electrical cable, therefore allowing for a range of cable sizes from small charging supply cables to large parallel sets of starter motor cables to be monitored for electrical faults.

In an additional or alternate form, the device 10 may include a temporal threshold adjustment means to selectively adjust the time period which the voltage differential is required to exceed the voltage differential threshold in order for the relay to be operated. In particular the temporal input control can be adjusted to set the temporal thresholds, for example between 0 seconds to 20 seconds.

In a preferable configuration, the detection circuit is configured to detect if the device 10 is disconnected from one of the two points 100, 110 of the electrical cable 120. In the event that the detection circuit 20 detects that the device 10 has been disconnected from one of the two points of the electrical cable, the detection circuit 20 actuates the relay 30 which may be used to restrict or prevent current passing through the electrical circuit 130.

In certain embodiments, the output of the device 10 includes a number of voltage free change over contacts which can be used to supply normally energised voltage coils or energise shunt trip coils. In certain embodiments, the device can include a relay driving circuit in electrical communication with the relay to ensure that the relay is operated in the event that there is a fault within the device 10.

In one configuration, the relay 30 is energised when the monitored electrical circuit 130 is operating within the defined thresholds. However, when a fault is detected, the relay 30 deenergises, wherein the relay driver circuit latches into a fault mode, thereby actuating the relay 30 to de-energise which may be used to operate additional circuit devices, in order so that no current is flowing through the monitored electrical cable 120 that is in electrical communication with the relay 30. This feature will be discussed with reference to Figure 4. In order to reset the device to again operate in a monitoring mode (i.e. current is again allowed to flow through the monitored electrical cable), manual operation of a reset input control, such as a push button, switch or the like, may be required.

It will be appreciated that the detection circuit 20 may be provided in the form of an analogue circuit or a digital circuit. It will be appreciated that in the event that the detection circuit is to operate digitally, a processing system, such as a microprocessor, a Field

Programmable Gate Array (FPGA), or a customised integrated chip may be used as the detection circuit. Referring to Figure 5, there is shown a block diagram of a processing system 500 which can be used as the detection circuit 20. In particular, the processing system 500 is formed from a processor 510 coupled to a memory 515, one or more input devices 520 including one or more input controls, an optional output device 530, and an external interface 540 interconnected via a bus 550.

The external interface 540 can include a number of input and output ports. In particular the external interface 540 may include a number of input ports including a first and second input port for receiving electrical input from the first and second points 100, 110 of the monitored electrical cable 120. Additionally, the external interface 540 may include one or more output ports including a first output port which is in electrical communication with the relay 30 to allow the processor 510 to actuate the opening and closing of the relay 30 accordingly.

Referring to Figure 4 there is shown a specific electrical schematic 400 of an example of the device 10 for detecting an electrical fault. It will be appreciated that whilst this specific example includes analogue circuitry, it will be appreciated by a person skilled in the art that other configurations are clearly possible. It will also be appreciated that the specific values disclosed in the electrical schematic are merely for clarity purposes as it will be appreciated by a person skilled in the art that various other valued electrical components may be used. The device discussed in relation to Figure 4 is in relation to monitoring an electrical cable between a battery supply (B+) and a starter motor (S+), however it will be appreciated that this is merely for clarity purposes and that the device could be used for monitoring other forms of electrical circuits.

Referring more specifically to Figure 4 the electrical schematic device is a multi-stage circuit including stage A, stage B and stage C as shown by dotted outline for clarity.

Stage A includes a voltage divider arrangement 410 to proportionally adjust the battery supply voltage (B+) sensed at the first point 100 on the electrical cable by the differential threshold (Vj). One or more potentiometers 411, 412 can be used, as shown in the electrical schematic 400 of the device 10, to set the differential threshold (Vj).

Stage A also includes a first comparator 401 to compare the adjusted battery supply voltage against the starter motor voltage sensed at the second point 110 on the monitored electrical cable 120. In the event that the adjusted battery supply voltage is greater than the starter motor voltage (i.e. the voltage difference between the first and second points of the electrical cable exceeds the differential threshold), the output of the first comparator 401 is set to high, otherwise the output remains low. Stage A can optionally include a second comparator 405 which can actuate a visual indicator, such as a light emitting diode 406 (LED) to indicate that the device is near tripping point (i.e. the voltage differential has been detected but the temporal time period needs to be satisfied in the next stage of the circuit).

Stage B is a time delay and latch circuit including a capacitor and a resistor configuration 420 for defining the temporal threshold which the voltage differential threshold is required to be exceeded prior to the relay 30 being operated. As shown in Figure 4, a potentiometer 421 may also be provided in stage B to adjust the temporal threshold defined by the arrangement of the electrical components. The voltage across the capacitor 422 is used as an input to a comparator 440 which compares this voltage across the capacitor 422 against a substantially constant proportion of the supply voltage Vcc of the device 10. It will be appreciated that when the output of stage A is a high impedance signal, the capacitor 422 charge increases over time thereby adjusting the input to the comparator 440 of stage B. After a period of high input provided to stage B, the capacitor voltage is larger than the substantially constant proportion of the supply voltage Vcc of the device 10, thereby causing the comparator 440 to output a low signal to the stage C, otherwise a high impedance signal is output by the comparator 440. Similarly to stage A, stage B can optionally include a visual indicator, such as an light emitting diode 445 (LED) to indicate the output of the respective stage.

Stage B also includes a latching circuit whereby when the output of comparator 440 is triggered by a fault and the output goes low, diode D1 pulls the comparator reference low holding the comparator in the low state. This can only be unlatched by removing the charge from capacitor 422 via switch 430.

Stage C is a driving circuit which is in electrical communication with the relay 470. In particular, stage C includes a comparator 450 which is configured as an inverter. In particular, a low signal is output from the comparator 450 in the event that a high signal is received from stage B, otherwise a high signal is output by the comparator 450.

The output signal of the comparator 450 in stage C is in electrical communication to the base pin of a PNP transistor 460. In the event that a negative signal has been output, the transistor is in an active mode of operation, wherein current flows through the collector of the PNP transistor 460 so that the relay 470 is closed. When the relay is closed, current flows through the load L. However, in the event that a high signal is output by the comparator 450 of the drive circuit, then the PNP transistor 460 operates in a non-active mode, wherein no current flows through the relay 470 to thereby opening the relay so that no current flows through the load L. As will also be appreciated from Figure 4, the relay 470 may include a protection diode 480 in parallel with the relay to reduce a voltage spike due to an inductive load. Additionally, similarly to stage A and B, a visual indicator 490, such as an LED, can be used to indicate the output of stage C.

Referring back to stage B of the electrical schematic, a reset switch 430 is provided which is in electrical communication with the electrical components forming the time delay circuit 420. In the event that the relay is operated, the user may be required to manually press the reset switch 430 of the device 10 in order to de-energise the capacitor 422, thereby resetting the device 10. As a result of the reset switch 430 being actuated, the drive circuit of stage B causes the relay 470 to close, thereby again allowing current to flow through the monitored electrical cable 120 of the respective electrical circuit 130. The device 10 is thereby ready to again monitor the voltage differential between the first and second points 100, 110 of the circuit 130 to determine if this exceeds the defined voltage differential threshold accordingly.

It will be appreciated that in the event that the inputs from the first point or the second point of the electrical cable are disconnected, the first comparator of stage A will output a high impedance signal, which results in the relay opening so that no current flows through the load L.

In an optional form, the device may be configured to automatically adjust the voltage differential threshold according to the resistance properties of the electrical cable. In one embodiment, properties such as the length and gauge of the electrical cable can be used to determine the resistance of the cable to calibrate current detection. In another embodiment, the device may include resistance measurement circuitry to measure the cable resistance between the points 100, 110, thereby allowing the determination of the voltage differential threshold. In another embodiment, an input unit, such as a keypad or the like, can be operated by a user to provide values such as the length and/or the gauge of the electrical cable which is being monitored between the two points 100, 110. The input values can then be used by the processor to set the voltage differential threshold which is stored in memory.

In particular embodiments, the device may include a configurable time delay for tripping the relay 30 in response to periods of inactivity from the load L. In particular, the device can include an inactivity temporal threshold input unit to allow the user to set an inactivity temporal threshold which is used to determine if the load has been inactive for a period of time which exceeds the inactivity temporal threshold. For example, considering the load being an engine, the device may receive an input from the engine indicative of whether the engine is/is not running. In another configuration, the device may be configured to measure the supply voltage to determine if the engine is running by the float charge provided by the engine alternator. In another configuration, the detection circuit can be configured to detect measure the current draw via the detection circuit on the battery cable to determine that the engine is/is not running.

In certain embodiments, the device is configured to detect if the load is failing to disengage or contacts of the load are “sticking” closed. In one configuration, the detection circuit can receive an input from the ignition switch to detect that the load is intended to be disengaged and detect a voltage differential between the two points, thereby detecting this fault condition.

In certain embodiments, the device can utilise one or more field inputs to dynamically adjust the sensitivity of the device to detect an electrical fault. For example, the threshold voltage differential can be dynamically altered by the device (increased or decreased) for particular operation modes of the load, for example decreasing the sensitivity of the device when a starter motor is engaged. In one form, the one or more field inputs are digital input. For example, the field input may be a signal from the ignition switch to decrease the sensitivity while cranking the engine but while the engine is running and not cranking it will lower the trip threshold to be more sensitive.

In certain embodiments, the output device 530 of the device 10 can include a display unit, such as an electronic screen. In particular, in the event that the detection circuit is a processing system, the processor is in electrical communication with the output device in the form of the electronic screen. The electronic screen can be controlled by the processor to present the current flowing through the conductor.

In certain embodiments, the processor of the device can record a log of faults detected in the memory of the device 10. Additionally, the memory can be configured to store selectable parameters, readings or measurements. The processing system can be configured to allow a user to selectively set trip thresholds, via the input device, which are then stored in memory and used by the processor to determine if a trip condition has been detected. Furthermore, the memory of the processing system may have stored therein data tables indicative of inverse or other current/time trip functions which the processing system can utilise to detect a trip condition.

The external interface of the processing system can be a communication interface to allow the device to communicate with other equipment for monitoring, controlled shutdown, configuration or log download. The communication interface may utilise a wired communication medium or may operate wirelessly.

The device can include a power supply to ensure correct operation of the device during times of high load when there is a high voltage drop to sufficiently power the device. For example, the power supply can be configured to ensure that the device operates when cranking of an engine occurs which experiences a fault. The device can also include a relay power supply to power the trip device (i.e. the relay 30) and ensure disconnection of the circuit. This can be beneficial in instances where there is a significant fault which results in insufficient power to operate the relay device. In this instance, the relay power supply provides sufficient power to the relay 30 to ensure that the relay is opened. However, as will be appreciated, in alternate configurations a particular relay device can be utilised which does not require power to be placed in an open position but rather maintained in the closed position.

In certain embodiments, the device can include configurable settings to detect failing loads, such as a starter motor beginning to bum out. For example, the processing system can store in memory a history of the current draw profile, wherein in the event that the profile varies with reference to the historical data by more than a historical threshold stored in memory, the device can provide a warning of a pending failure. For example, an audio and/or visual alarm may be presented via the output device 530.

In certain embodiments, the device can include under voltage and/or over voltage detection circuitry to present a warning or alarm via the output device 530 of the device. Additionally or alternatively, the under/over voltage detection circuitry can cause the relay 30 to trip after a particular temporal threshold is met when the battery voltage fails to satisfy an acceptable voltage range. In one form, the upper and/or lower battery voltage thresholds and the temporal threshold can be configurable via the input means of the device and stored in memory.

In certain embodiments, the device may include multiple detection circuits such that multiple electrical cables can be monitored.

Whilst the device described herein can be used for many types of applications, it will be appreciated that the device has particular application in high current draw applications, such as the operation of engines.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

Claims

1. A device for detecting an electrical fault in an electrical circuit, wherein the device is in electrical communication across two points of a single electrical conductor of the electrical circuit, the two points of the single electrical conductor being spaced apart along the electrical conductor and there being no other electrical components between the two points of the single electrical conductor, wherein the device includes a detection circuit to detect a voltage differential, across the two points of the single electrical conductor, which exceeds a voltage differential threshold for a threshold period of time, and to output the detection to a relay to prevent current being supplied through the electrical conductor in the event of a successful detection.
2. The device according to claim 1, wherein the device includes the relay.
3. The device according to claim 2, wherein the device includes a relay power supply to supply electrical power to the relay when the current is prevented from flowing through the single electrical conductor.
4. The device according to any one of claims 1 to 3, wherein the voltage differential threshold is proportional to a supply voltage of the electrical circuit.
5. The device according to claim 4, wherein the proportional relationship between the voltage differential threshold and the supply voltage is selectively adjustable via a voltage differential threshold adjustment means.
6. The device according to claim 5, wherein one or more properties of the single electrical cable are obtained to adjust the voltage differential threshold.
7. The device according to claim 6, wherein the one or more properties are input via an input means.
8. The device according to claim 6 or 7, wherein the one or more properties include at least one of: a resistance of the single electrical conductor; a gauge of the single electrical conductor; and a length between the two points of the single electrical conductor.
9. The device according to claim 8, wherein the device includes a resistance detection circuit to detect the resistance of the single electrical conductor.
10. The device according to claim 9, wherein the device dynamically adjusts the threshold voltage in response to a detected mode of operation of the load.
11. The device according to any one of claims 1 to 10, wherein the threshold period of time is selectively adjustable via a temporal threshold adjustment means.
12. The device according to any one of claims 1 to 11, wherein the detection circuit is configured to detect if the device is disconnected from one of the two points of the single electrical conductor, wherein in response to detecting that the device is disconnected from one of the two points of the single electrical conductor, the detection circuitry actuates the relay to prevent current passing through the single electrical conductor.
13. The device according to any one of claims 1 to 12, wherein the detection circuit includes a device power supply to provide electrical power to the device in the event that insufficient electrical power is provided from the single electrical conductor due to the operation of the load.
14. The device according to any one of claims 1 to 13, wherein the device includes a inactivity temporal threshold input means to set an inactivity temporal threshold, wherein the device includes an input port to receive a feedback signal from the load indicative of the activity of the load, wherein in the event that the feedback signal is indicative that the load has been inactive for a period of time which equals or exceeds the inactivity temporal threshold, the relay is actuated to prevent current passing through the single electrical conductor.
15. The device according to any one of claims 1 to 14, wherein the detection circuit is a processing system.
16. The device according to claim 15, wherein the processing system includes a processor in electrical communication with memory, an input means and an output means.
17. The device according to claim 16, wherein the processor records measurements detected from the two points of the single electrical conductor in a log in the memory.
18. The device according to claim 17, wherein the processor compares measurements detected from the two points of the electrical conductor against the log, wherein in the event the event of a discrepancy between the measurements and the log which exceeds a comparison threshold, the device presents a warning via the output means.
19. The device according to claim 16 to 18, wherein the processing system includes a communication interface to allow communication of data with an external device.
20. The device according to claim 16 to 19, wherein the processor presents a detected current flowing through the single electrical conductor via the output means.