Synchronisation of devices concurrently measuring electrical parameters

Abstract

A method is disclosed for synchronisation of measurement data obtained and transmitted to a user device by two or more respective electrical parameter measuring devices that obtain measurements concurrently. Each measuring device can communicate wirelessly with other measuring devices, and at least one of the measuring devices is a contactless measuring device. In the method, at least while the measuring devices are concurrently obtaining measurements, one or more signals are transmitted between the measuring devices, and time-related information associated with the one or more signals transmitted between measuring devices is used to synchronise measurement data obtained by each of the respective measuring devices, or to allow measurement data obtained by each of the respective measuring devices to be synchronised.

Description

SYNCHRONISATION OF DEVICES CONCURRENTLY MEASURING ELECTRICAL PARAMETERSTECHNICAL FIELD

[0001] The present invention relates generally the measurement of electrical parameters (i.e. the measurement of parameters associated with electrical flows), and more specifically, to the synchronisation of multiple devices that are concurrently measuring electrical parameters.BACKGROUND

[0002] Multimeters are one form of device that can be used to measure parameters associated with an electrical flow in, for example, a circuit or piece of electrical / electronic equipment, or in a wire or other conducting element that forms part of such equipment. Most multimeters can measure: voltage (either alternating current (AC) or direct current (DC)), current (which, again, can be either AC or DC), and resistance.

[0003] Some multimeters can also measure other or additional electrical (or associated) parameters, including (but not necessarily limited to) capacitance, frequency (for AC currents), inductance, temperature, etc.

[0004] Most multimeters have test probes which can be placed in electrical (i.e. in physical, conducting) contact with the relevant wire (or other electricity carrying conductor) from which measurements are to be taken using the multimeter. More specifically, most multimeters have a pair of flexible electrical leads / cables extending from the main housing / body of the multimeter, where the inner ends of these cables are electrically connected to the electronics and circuitry housed inside the multimeter’s main housing / body, and on the outer end of each of these cables is a conductive test probe. These probes on the ends of the multimeter’s flexible leads / cables can take a range of forms, such as e.g. simple pointed metal conducting tips (typically these also have insulated handles to enable them to be held / used by the user), or they may take the form of clips or other attachment mechanisms which are made from conductive material and also able to be attached / secured to the wire or other conductor from which measurements are to be taken (so that they do not need to be physically held in place manually by the user). Whatever their form, these conductive probes on the ends of the multimeter’s leads must generally be placed in physical conducting contact with the particular wire or other conductive element from which the relevant electrical parameter(s) is / are to be measured, and when the conductiveends / portions of the probes are in contact with the wire / conductor from which the measurements are to be taken (and with the multimeter turned on and set to the relevant mode, such as e.g. voltmeter mode if the parameter to be measured is voltage, or ammeter mode if the parameter be measured is current, etc) electricity flows into the probes, and thus through the multimeter’s leads and also through the multimeter whose internal electrical / measuring equipment measures the desired parameter(s). The main body / housing of many multimeters also often has a display, such as e.g. an analogue gauge with a needle, or a digital display / readout, or a screen, etc, for displaying the measured parameter(s) to the user.

[0005] The kinds of multimeters just described, namely those with conductive test probes connected to the multimeter (i.e. to the multimeter’s main body / housing) via flexible conductive leads / cables, are generally suitable for measuring parameters like voltage. The reason is because, to measure voltage, the multimeter (and in particular the measuring equipment contained within the multimeter) needs simply to be connected to the wire or other conductor (from which the voltage measurement is to be taken) in parallel. This can be done simply by placing the conductive probes on the respective ends of the multimeter’s leads (or attaching these probes, if they are clips or other attachable-type probes) in physical (and hence electrical conducting) contact with the wire from which the voltage measurement is to be taken, and doing this thereby connects the multimeter to the wire / conductor (from which the voltage measurement is to be taken) in parallel, thereby enabling the voltage measurement(s) to be taken.

[0006] However, using multimeters (and similarly other kinds of measuring devices), which use / require test probes (or the like) that must be placed in physical conducting contact with the wire or other conductor from which measurements are to be taken, can be more difficult when the parameter required to be measured is, for example, current. One of the reasons for this is because, in order to take current measurements (i.e. in order to measure current) with a device that uses conductive test probes that must be physically (conductively) connected to the wire or other conductor from which the current measurement is to be taken (as is the case for e.g. the multimeters described above), the device (multimeter or other device) must be connected to the wire / conductor from which the current measurement(s) is / are to be taken in series. This can often give rise to considerable difficulty in practice because, often, this is not easy or simple to do. Consider, as merely one illustrative example, that in copper refineries (and similarly other electro-metallurgical refineries) there is often a need to measure the current flowing in the individual “busbars” associated with the refinery’s various electrolytic cells. The busbars used in these electrolytic cells are huge conductors typically made from thick, solid metal. In order to measure the current flowing in one of these “busbars” using a device that must be physically connected “in series”, the conductor (i.e. the busbar in this example) often needs to be cut (orsimilar), so that the measuring device can be installed “in series” therein. This is often simply not practical (or even possible). For example, in the above example, it simply may not be practical to cut a busbar to allow a current measuring device to be installed. Or, even where (in other applications) installing a current measuring device (of the type that uses / requires test probes that must be placed in physical conducting contact with the conductor from which measurements are to be taken) “in series” is possible, installing such a measuring device can still be extremely difficult. Indeed, where (or if) this is to be done, it is often necessary for the whole piece of equipment from which current measurements are to be taken (and often other pieces of associated or linked equipment as well) to be shut down (or powered down or at least electrically isolated) first, to enable the measuring device to be connected or installed (in series) in the particular wire or other conductor from which the required measurement is to be taken. In other words, the connection or installation of the measuring device must be performed and completed while the piece of equipment from which current measurements are to be taken (at least) is powered down or electrically isolated. Once the measuring device has been installed, the equipment then needs to be restarted or powered back up (or reconnected or otherwise brought back into operation) so that the current measurement can be taken while the equipment is in operation. The equipment (from which the current measurement is / was taken) may then also need to be shut down (or powered down, or isolated) again to enable the measurement device (multimeter or other device) to be disconnected and removed (if this is necessary). All of this can be time-consuming and laborious (if it is even possible or practical). It can also be expensive when (in addition to the cost of the measurement device itself and the cost associated with its installation) costs associated with equipment downtime are also accounted for.

[0007] In light of the above, it is often considered preferable to use “contactless” measuring devices to measure electrical current. So-called “current clamps” (also sometimes known as “current probes”) are one type of “contactless” measuring device that can be used to measure current. Current clamps are “contactless” in the sense that they do not require (i.e. they do not need to be installed e.g. with contact probes or the like in) physical conducting contact with the wire or other conductor in which the current flow is to be measured. In a current clamp, instead of having test probes that must be placed in physical conducting contact with the conductor from which measurements are to be taken (as is the case for e.g. the multimeters described above), most current clamps are configured to form a closed loop around (but not in electrically conductive contact with) the wire or other conductor from which current measurements are to be taken. Many current clamps are designed with a pair of “jaws” that can first be opened (or moved apart, or separated, relative to one another) to enable the current clamp to be initially installed onto (or placed over) the particular wire or conductor from which current measurements are to be taken (i.e. with one of the jaws passing to one side of the conductor and the other jaw passingto the other side of the conductor), and then, once the current clamp is correctly in position, the jaws can be closed (or brought back together) around the wire or conductor thereby forming an effectively closed loop around the wire or conductor from which current flow is required to be measured. Once installed, a current clamp can measure the current flow in the wire or conductor using magnetic induction, and thus without requiring direct conductive contact with the wire / conductor. (In very simplistic terms, the way many current clamps work is that the flow of current in the wire or conductor being measured produces a magnetic field, and this magnetic field is measured by the current clamp using a Hall effect sensor - according to Ampere’s Law, the magnetic field around a conductor is proportional to the current.)

[0008] Thus, current clamps are “contactless” in the sense that they can measure current without requiring conducting contact (and indeed without necessarily requiring any physical contact) with the wire or other conductor carrying the electrical flow from which the current measurement is being taken.

[0009] Current clamps can be particularly useful for measuring the magnitude of alternating current (AC) flows, and many are also provided with additional measuring equipment and instrumentation to allow them (or multiple of them, used together concurrently) to also measure phase and waveform parameters associated with AC current flows. Some (but not all) current clamps can also measure direct current (DC) current flows.

[0010] As explained above, once a current clamp has been installed and closed around the wire or other conductor from which current measurements are to be taken (and with the current clamp turned on and, if necessary, set to the appropriate measuring mode), current measurements can be taken without any need to place or install any part of the device taking the current measurements (i.e. the current clamp) in direct physical / conducting contact with the wire or other conductor from which the current measurements are being taken, and in particular, without the need to install the measuring device (or any physical conductive contact-requiring probes thereof) in series with (or in) the conductor. This can greatly improve the ease and convenience of use of the device used for measuring current. Indeed, it is often much easier to simply install a current clamp on (around) the wire or other conductor (from which measurements are to be taken) rather than having to install a multimeter (or other measurement device) that requires physical conducting contact with the conductor (because, as described above, such “contact-requiring” measuring devices also need to be installed with the device’s contact (or other conductive) probes connected in series with the wire being measured, and this therefore often requires the equipment to be powered down to allow for installation of the measuring device, etc. (if it is possible at all), as described above).

[0011] There are, however, also some difficulties or challenges that can sometimes be associated with the use of current clamps (and also other forms of “contactless” devices used for measuring electrical parameters). Some of these difficulties arise due to the size of many existing current clamps (and other similar devices). They are often large and / or bulky, which can make them difficult to use in some situations, particularly in situations where the piece of equipment from which current measurements need to be taken are difficult to reach or access, and / or located in a confined / tight space. Sometimes, there may not be enough room in the space / region where the conductor (from which the measurement is to be taken) is located for a current clamp to be installed. That is, the current clamp simply may not fit in the place where it needs to be installed in order to take the required measurement. The size and / or bulk and / or shape of many existing current clamps can also make them less portable (particularly where multiple or a number of them are required to be transported), which is a particular issue given that technicians who are required to make use of these devices are often operating / working out in the field and therefore must carry / transport all of the required measuring devices to the location where they are to be used (and the larger or more bulky or cumbersome the measuring devices are, the more difficult they can be to transport).

[0012] One way in which these challenges have recently been addressed (and the same has also been done for multimeters with physical contact test probes, which can suffer from similar challenges) is by providing the measuring devices (e.g. current clamp or multimeter or other measuring devices) without a display / screen on the device itself, and possibly also without (or with fewer of) the controls (e.g. buttons, dials, etc, for controlling the operation of the device) being provided on the body of the device. Or, sometimes, the measuring device may still be provided with a screen or other display, but it may be smaller and therefore more limited in terms of what information it is able to display. Where this is done (and in particular, where the device is provided without a screen or other display on the body of the device, but also where a smaller display is provided), this can help to significantly reduce the overall size of the main body / housing of the measuring device, thereby making the device overall more compact (i.e. smaller), and therefore easier to install and use particularly in confined or difficult to access locations, and also easier to transport (particularly where multiple of the devices must be transported). Thus, the smaller size of the devices may enable them to be used in places where other, larger devices (with screens (or larger screens) and / or more controls on the body of the device) may not fit. Another benefit of this is that, by eliminating (and not providing) the display / screen (and possibly also some or all of the controls) on the body of device (or by at least providing a smaller screen), there is also no need to include the electronics that would otherwise be required to enable these to operate (or the amount and complexity of these electronics may be reduced if the functionality of the screen / display is reduced). This can also help to simplify the design, and potentially alsoto further reduce the size, of the device. It can also make the device cheaper and simpler to produce, allow it to consume less power when in operation (therefore requiring a smaller battery, or able to operate longer), etc.

[0013] Therefore, providing the measuring device (e.g. current clamp or multimeter or other device) without a display / screen on the device itself (or a smaller one), and possibly also without (or with fewer of) the controls on the body of the device, can have a number of advantages. However, it also gives rise to certain additional requirements, including, in particular (and possibly in addition to other things), the need to (in some other way) display the measurements taken using the device, given that the device does not have its own screen or other display or read out for displaying the measurements being taken (or, even if it does have a smaller, more limited screen I display, there may still be a need to display measurements taken which are unable to be shown / represented on that smaller display). If some or all of the controls are also removed from the device itself, there is also a need to be able to operate the device, or to operate / control those aspects of its functioning for which the controls are no longer provided on the body of the device, remotely or in some other way.

[0014] In recent times, the additional requirements mentioned in the previous paragraph have been achieved by creating devices for measuring electrical parameters which are able to connect with (i.e. establish a data connection with) a nearby electronic device which has a screen, such as e.g. the user’s mobile phone, or tablet computer, or laptop, or the like. Often, an application or software is provided (i.e. installed on the user’s device (phone, tablet, laptop, etc)), and the application / software enables the mobile device to receive measurements (or measurement data) from the measuring device (or from multiple measuring devices) and display it in an appropriate format (e.g. numerical format, graphical format, etc) on the screen of the user’s device. Often, the application / software also enables the operation (or at least certain aspects of the operation) of the measuring device to be controlled from the mobile device. This can also have the advantage that being able to control the device, and view measurements / data obtained from the device, remotely (or from a distance away from where the device is located when taking the measurements) can be more convenient, and sometimes safer, given that the device may sometimes be used in tight or confined spaces, etc, as discussed above. Also, sometimes, if the measuring device has a display, if the device is installed to take measurements in a confined space, it may not be possible for the user to see the display on the device to read the measurements.

[0015] It is generally preferable for (and it has generally been the case that) the measuring device (on the one hand), and the user device such as e.g. a phone or tablet or laptop (on the other head), are connected wirelessly, so that there is no connecting cable required to transmitdata between the measuring device and the user device. Reasons for this include, for example, the ability to read / see measurements from a location remote (or away) from the location of the measuring device, the ability to read the measurements in a way (or from a location) that is electrically isolated from the current-carrying conductor from which measurements are being taken (which is safer), and of course, the inherent convenience of not requiring cables. Furthermore, usually, this wireless connection between the (or each) measuring device and the user device (with a screen, e.g. a phone) is established using Bluetooth (or BLE, which stands for Bluetooth Low Energy - hereafter in this specification, reference to Bluetooth should be understood to include BLE). The main reason for the use of Bluetooth (instead of other existing technologies that enable wireless connectivity) is due to the ubiquity of Bluetooth. Almost all mobile phones, tablet computers, laptops, etc, have Bluetooth, and therefore Bluetooth is usually chosen / used as the means by which a wireless connection can be established between the user device (e.g. which may be e.g. a mobile phone, or tablet, or laptop) and the / each (often screenless) measuring device used for measuring electrical parameters. There are also certain other advantages to using Bluetooth, such as e.g. it’s relatively low power requirements (and consequently lower battery drain), etc, compared to other wireless connectivity technologies like Wi-Fi.

[0016] Whilst Bluetooth is therefore usually chosen / used as the means by which the wireless connection is able to established between the user’s device (e.g. mobile phone) and the I each (often screen-less) measuring device, there are also certain problems and challenges associated with the use of Bluetooth, particularly when there is a need to obtain measurements using (i.e. measurements from) multiple measurement devices concurrently, as explained below.

[0017] There can sometimes be (in fact there is often) a need to use multiple different measuring devices to measure different electrical parameters concurrently. For example, in three-phase power applications, a separate current clamp (or other measuring device) may be required to measure current in each phase, and in such situations, accurate measurements of e.g. current load of a multiphase system (for example) can generally only be made using measurements from all phases (and hence from all current clamps) taken concurrently. Concurrent voltage measurements are also needed if power is to be measured or calculated. There may also be other situations where there is a need to, for example, measure both voltage and current concurrently, and where each parameter needs to be measured using a different measuring device. For example, the phase between current and voltage is needed to determine e.g. whether a load is real, inductive or capacitive.

[0018] However, in these (and indeed the numerous other possible) scenarios where multiple devices are needed to be used to measure electrical parameters concurrently, there isvery often also a need (in fact in many situations it is essential) for the respective measurement devices to be synchronised with one another in time. In other words, it is often essential for the data corresponding to the measurements being obtained by each separate measuring device to be aligned in time. To put it another way, if / where a measurement is being displayed on the user device’s screen as having been obtained by one measuring device at a particular moment / instant in time, and if another measurement is also being displayed as having been obtained by another (separate) measuring device at that same moment / instant in time, it is often essential to be sure / confident that those two measurements (taken by the two separate measurement devices) were actually taken at the very same moment / instant in time. Otherwise (i.e. if this is not known or not certain), it may not be possible to perform a wide range of necessary calculations accurately (or at least there may be uncertainty as to the accuracy of such calculations).

[0019] The reason this, in particular, poses a challenge is because Bluetooth (which is very often the means by which a wireless connection is established) does not provide a real-time data connection. On the contrary, Bluetooth can have a considerable amount of latency in both data transmission and data reception.1This is, to a large degree, an inherent and unavoidable part1Bluetooth is not considered real-time and is subject to indeterminate latency for several key reasons:1. Packet-based TransmissionBluetooth operates using packet-based communication, where data is divided into small packets that are transmitted across a shared wireless channel. This means that even though data may be sent rapidly, there are no guarantees on exactly when a specific packet will be sent or received due to network congestion or interference.2. Channel Hopping and InterferenceBluetooth uses a technique called frequency-hopping spread spectrum (FHSS), where it switches between different frequencies within the Bluetooth spectrum to avoid interference. This can cause latency because the device needs to sync with these frequency changes, and in busy environments with many devices, interference can increase, further delaying transmission.3. Shared Bandwidth and Collision AvoidanceBluetooth operates in the 2.4 GHz ISM band, which is also used by Wi-Fi, microwaves, and other wireless devices. When multiple devices try to use the same frequency, Bluetooth must use collision avoidance techniques (like retransmitting lost packets), which adds unpredictable delays.4. Bluetooth Stack and Protocol OverheadBluetooth's protocol stack (like L2CAP, HCI, etc.) includes layers that add overhead, increasing latency. Data passes through these layers, adding delays, especially in complex devices where processing might take longer. The stack isn't optimized for ultra-low-latency operation.5. Low Power Modes and Sleep StatesBluetooth devices, especially in low-energy (BLE) modes, often enter sleep states to save power. Waking up from these states introduces latency since the device has to resume operations before it can transmit or receive data.6. Buffering and RetransmissionBluetooth often buffers data to ensure smooth transmission, and if any data packet is lost or corrupted due to interference, it must be retransmitted. These retransmissions introduce additional delays, further preventing it from being real-time.7. Jitter and Timing VariabilityBluetooth is subject to jitter, where the delay in transmitting or receiving data can vary unpredictably. In realtime systems, predictable timing is crucial, but Bluetooth's variable delay, due to the factors above, makes it unsuitable for strict real-time applications.of the way Bluetooth works, due to the way it prioritises and assigns transmission and reception of data packets. The result is that it generally cannot be known (and it is not even predictable), for example, how much a particular data transmission received from a particular measurement device is affected by a time delay due to Bluetooth latency (or what the delay for that particular data transmission is / was). Consequently, where data is transmitted by multiple measurement devices to a user device (mobile phone), it is also not possible to know how much each data transmission has been affected by time delay (or how much they differ), and consequently it cannot be known whether data transmitted by each device is “aligned in time”, and because this is not known / certain, is not possible to perform calculations with confidence based on the data transmitted by the multiple different measuring devices.

[0020] It is against this background that the present invention has been developed.SUMMARY OF THE INVENTION

[0021] In one form, albeit not necessarily the only or broadest form, the invention relates to a method for synchronisation of measurement data obtained and transmitted to a user device by two or more respective electrical parameter measuring devices that obtain measurements concurrently, wherein each measuring device can communicate wirelessly with other measuring devices and at least one of the measuring devices is a contactless measuring device, and in the method at least while the measuring devices are concurrently obtaining measurements, one or more signals are transmitted between the measuring devices, and time-related information associated with the one or more signals transmitted between measuring devices is used to synchronise (align in time) measurement data obtained by each of the respective measuring devices, or to allow measurement data obtained by each of the respective measuring devices to be synchronised (aligned in time).

[0022] In some embodiments, measurement data obtained by the two or more measuring devices concurrently may be transmitted to the user device via Bluetooth.

[0023] Also, in some embodiments, each measuring device may communicate with other measuring devices via radiofrequency (RF) communication.

[0024] Prior to commencing acquisition of measurements concurrently (i.e. prior to commencing sampling and storing the measurements that will, along with measurements from other measuring devices, later be transmitted to the user device), each measuring device may establish a wireless connection with the user device.

[0025] In some embodiments (but not necessarily all embodiments), prior to commencing acquisition of measurements concurrently, one measuring device may be designated to operate as a master measuring device and the (one or more) other measuring device(s) may be designated to operate as slave measuring device(s).

[0026] In some implementations, acquisition of measurements concurrently by the two or more measuring devices may commence upon the occurrence of a trigger event. Often, the two or more measuring devices may commence sampling prior to the commencement of the concurrent acquisition of measurements. In some embodiments, the trigger event may be a predetermined event that, if or when it occurs, is able to be detected by one of the measuring devices. In these embodiments, the measuring device that is able to detect the predetermined trigger event may be designated as a master measuring device, and the other measuring device(s) may be designated as slave measuring device(s), and upon the detection by the master measuring device of the predetermined trigger event occurring, the master measuring device may commence acquiring measurements of the parameter(s) it is measuring and it may transmit a trigger signal to each other (slave) measuring device causing each of them to concurrently commence acquiring measurements of the parameter(s) they are each measuring.

[0027] In the embodiments just described, the trigger signal, or alternatively some other signal sent to each measuring device, may inform each measuring device of one or both of: how long it should continue acquiring measurements following the commencement of acquisition of measurements; and the sampling rate to be used by each measuring device.

[0028] In general, after completion of the concurrent acquisition of measurements by the two or more measuring devices, each measuring device may transmit measurements it acquired to the user device.

[0029] Measurement data received by the user device from the two or more measuring devices may be caused to be synchronised by causing the timing of the sampling (i.e. by causing the timing of the taking of measurements) by each respective measuring device to be synchronised (at least during the concurrent acquisition of measurements).

[0030] In some embodiments, measurement data received by the user device from the two or more measuring devices may be caused to be synchronised by causing the timing of the sampling by each respective measuring device, and the period of (concurrent) acquisition for each measuring device (i.e. the time window during which the respective measuring devices are acquiring measurements), to be synchronised (at least during the concurrent acquisition of measurements).

[0031] Each measuring device may have a counter which increments (or decrements) (by one or by some other amount) at each cycle of the counter, and when the value of the counter reaches a predefined value (COUNTERVAL) the measuring device is caused to sample (i.e. to take a measurement of the parameter(s) it is measuring) and reset the value of the counter (the counter may be reset e.g. to zero or otherwise to its initial / staring value).

[0032] In some embodiments, the master measuring device may periodically transmit synchronisation signals to each slave measuring device, wherein each synchronisation signal sent to each slave measuring device contains the current value of the counter of the master measuring device (i.e. the “master counter value”), and upon receipt of a synchronisation signal (containing the “master counter value”) each slave measuring device updates / changes the current value of its own counter to match (i.e. to make it the same as) the current value of the counter of the master measuring device (i.e. to make it the same as the “master counter value”).

[0033] Alternatively, in some other embodiments, the master measuring device may periodically transmit synchronisation signals to each slave measuring device, wherein each synchronisation signal sent to each slave measuring device instructs the slave measuring device to (if necessary) change its predefined value (i.e. to change its COUNTERVAL, which is the predefined value at which that slave device samples (i.e. takes a measurement) and resets the value of its counter) to synchronise the timing of when the slave measuring device samples (i.e. when it takes a measurement) with the timing of when the master measuring device samples (i.e. when it takes a measurement).

[0034] There may be a clock associated with each measuring device, and in some embodiments, measurement data received by the user device from the two or more measuring devices may be caused to be synchronised by causing the clocks associated with each of the measuring devices to remain synchronised, and the clock data may be used to:- timestamp data to allow information included in the data from all devices to subsequently be used to (e.g. after it has been transmitted to the user device) to align the data from all devices in time, and / or- synchronise sampling by the measuring devices.

[0035] One measuring device (which may be, but need not necessarily be, the (or a) master measuring device) may transmit at least one synchronisation signal to each other measuring device, which may include data about a particular event (or set of events) that the said one measuring device has detected, or about a particular measurement (or set of amendments) that the said one measuring device has taken, and the synchronisation signal also includes information about the timing of when the said event(s) or measurement(s) were detected / takenby the said one measuring device and the said one measuring device itself also records this time information, and when the synchronisation signal is received by each other device, each of the said other devices may be able to determine the time (according to a clock / counter of the said other device itself) when the event(s) / measurement(s) were detected / taken by the said one device.

[0036] In the embodiments just described, each said other device may identify particular measurement(s) that it was taking (or took) at the time when the event(s) / measurement(s) were detected / taken by the said one device, and the said other measuring device may “event-stamp” the particular measurement(s) that it took at the time when the said one device was detecting / taking the event(s) / measurement(s) about which the said one device included information in the synchronisation signal. This “event-stamp” information may be included in the data that is “acquired” by each said other device for later transmission to the user device. After the data from the one or more respective other devices, and from the said one device, are received by the user device, the “event-stamp” information contained in the data from each said other measuring device, together with the timing information recorded by the said one measuring device, may be able to be used to align the data received from each said other device in time with the data received from the said one device.

[0037] Other features and aspects of the invention will be made evident from the Detailed Description below.BRIEF DESCRIPTION OF THE FIGURES

[0038] Features, embodiments and / or variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the invention, whether as summarised in the preceding Summary of the Invention or as set out in the appended Claims (if any), or otherwise. The Detailed Description below makes reference to a number of Figures as follows:

[0039] Figure 1 illustrates, albeit in a very simple, schematic way, multiple measuring devices (each for measuring one or more electrical parameters) that are in operation concurrently and which are connected to (i.e. they have a data connection with) a user device (e.g. a mobile phone, tablet or the like) on which the measurement data from the measuring devices can be displayed (and the user device may also be operable to control the operation of each measuring device, or at least aspects of their operation).

[0040] Figure 2 is a schematic representation of the procedure by which the multiplemeasuring devices establish a connection (data connection) with the user device.

[0041] Figure 3 is a schematic representation of the way the multiple measuring devices (after they are connected to the user device) can operate.DETAILED DESCRIPTION

[0042] As mentioned above, Figure 1 illustrates, in a very simple, schematic way, multiple measuring devices (each for measuring one or more electrical parameters) that are in operation concurrently (i.e. where all of the measuring devices are in operation (taking measurements) at the same time), and where the multiple measuring devices are wirelessly connected to (i.e. they each have a wireless data connection with) a user device (which may be e.g. the user’s mobile phone, a tablet, or the like) on which the measurement data from the measuring devices, or analysis performed based thereon, can be displayed or performed. The user device may also be (and typically is) operable to control the operation (or at least aspects of the operation) of each measuring device. There is also wireless communication / signalling between the individual measuring devices, as discussed below.

[0043] The number of measuring devices depicted in Figure 1 (all wirelessly connected to the user device) happens to be three. However, this is simply for illustrative purposes. No limitation whatsoever is to be inferred from this. Indeed, there is no limitation on the number of measuring devices that may be connected to the user device and used (to measure electrical parameters) concurrently. Therefore, the number of measuring devices in operation concurrently and connected to the user device could be as few as two, or there may be three (as shown), or there may be more than three (and this is what the dashed lines in Figure 1 is intended to indicate). There is no upper limit on the number of measuring devices. Technically, there could also be only a single measuring device measuring electrical parameters and connected wirelessly to the user device. However, in that (single measuring device) case, there would be no need for synchronisation between multiple measuring devices.

[0044] At least one of the measuring devices is a contactless measuring device. In fact, all of the measuring devices may be contactless measuring devices. However, the latter is not a requirement. The respective measuring devices may all be the same kind of (contactless) measuring device, or some may be different kinds of measuring devices to others (and some may be contactless and others not). For example, in one possible scenario the devices could all be contactless current clamps. However, in another possible scenario, one (or multiple) of the measuring devices might be a current clamp (and / or some other form of contactless measuring device for measuring one or more electrical parameters) while one (or multiple) other devices might be a different kind of device such as, e.g. a multimeter, which may not be contactless.

[0045] Generally, the multiple measuring devices will all be connected, typically (preferably) wirelessly, to the user device (e.g. mobile phone or the like), and for reasons discussed above, the wireless connection between the user device and the respective measuring devices will typically be achieved using Bluetooth. However, other technologies for establishing a wireless connection between each measuring device and the user device could also be used, such as e.g. Wi-Fi. A combination of technologies could also be used, for example, Bluetooth may be used sometimes, and Wi-Fi (or some other wireless technology) may be used at other times. Also, some measuring devices could connect via Bluetooth while others simultaneously connect via Wi-Fi (or some other wireless technology). Thus, the invention is not necessarily restricted to use only with Bluetooth as the technology for establishing the connections between each measuring device and the user device. In fact, it is even possible that one or more (or even all) of the measuring devices could be connected to the user device by a cable (or wired) connection, although it is thought that such a wired connection will rarely be used between the user device and one or more (or any) of the respective measuring devices. One reason for this is because of the practical difficulties created by a wired connection. Also, there may be (at least potential) risks / dangers associated with the use of a cable connection because, if even one of the measuring devices is connected to the user device by a cable, then there is an electrical conductor (the cable) extending between that measuring device (and whatever conductor with electricity following therein that measuring device is measuring) and the user device. It is often preferred not to have any such electrical conductor (cable or otherwise) extending between (and connecting) a measuring device (and what it is measuring) and the user device. Therefore, users normally prefer a wireless connection between each respective measuring device and the user device, including for the additional safety achieved by this (because the user device and user are (electrically and physically) isolated from the measuring devices), as well as for the improved convenience wireless connections provide.

[0046] Turning now to Figure 2, as mentioned above, this is a schematic representation of the procedure by which the multiple (two or more) measuring devices establish a connection (data connection) with the user device. It is important to note from the outset that the procedures shown in Figures 2 and 3 (and discussed below) are given by way of example only. The invention is not necessarily limited to or by these.

[0047] The schematic representation in Figure 2 has three columns. The column on the left in Figure 2 represents the user device. The column in the middle in Figure 2 represents a first measuring device, which is merely one out of the multiple measuring devices that are to be in operation concurrently and wirelessly connected to the user device. The column on the right in Figure 2 represents each of the one or more further measuring device(s). Therefore, the columnon the right in Figure 2 represents all of the other measuring devices that will be concurrently used, i.e. other than (or, in other words, in addition to) the first measuring device (which is represented in the middle column in Figure 2). It will be understood that, therefore, the column on the right in Figure 2 could represent only one other measuring device if the total number of measuring devices that will be concurrently used is two, or the column on the right in Figure 2 could represent two (or three or four) other measuring devices if the total number of measuring devices that will be concurrently used is three (or four or five), etc.

[0048] In any event, Figure 2 illustrates the signalling interactions between the user device and the various measuring devices to establish a data connection between the user device and each of the measuring devices respectively.

[0049] At step 2 in Figure 2, the user device is initiated. Typically, this will involve an application (or software) that is installed on the user device (for displaying measurements / data received from the measuring devices, or perhaps the results of any analysis thereof, and also for controlling the measuring devices, etc) being launched / opened on the user device.

[0050] Meanwhile, the first measuring device, which is represented in the middle column in Figure 2 (and which, it will be recalled, is merely one of the two or more measuring devices that are to be used concurrently, and this will typically be the first / initial one to establish a connection with the user device) is initiated at step 4. Also, the (or each of the) further measuring device(s) are also initiated at step 6.

[0051] In Figure 2, there is a stage / step 3 shown following step 2. As discussed below, this is a stage that the process returns to after a transmission of measurements from the measuring devices to the user device has been performed / completed. Similarly, there is a stage 5 shown following each of steps 4 and 6 in Figure 2. This (stage 5) is also a stage that the process returns to after a transmission of measurements from the measuring devices to the user device has been performed / completed, as discussed further below.

[0052] After the first measuring device has been initiated at step 4, and similarly after each further measuring device has been initiated at step 6, the measuring devices (i.e. the first and each further measuring device) advertise - that is, each one sends a broadcast signal, or alternatively each one may send a signal direct to the user device - indicating that it is available for connection to the user device.

[0053] Next, as shown in the left-hand column in Figure 2, at the next step 8, the user device sends a connection request signal to the first measuring device. (Recall that the first measuring device is simply one from among the two or more measuring devices from which the user devicehas, by this stage, received an advertisement signal indicating availability for connection. Often the first measuring device will be the one measuring device from which such an advertisement signal is received first / earliest by the user device, but this need not be the case, i.e. this is not essential or even important, and the first measuring device could alternatively be a measuring device from which the advertisement signal is not the first / earliest to be received by the user device).

[0054] After sending the connection request signal to the first measuring device at step 8, the user device then waits for a data connection with the first measuring device to be established (i.e. the user device awaits an acknowledgement signal from the first measuring device confirming the establishment of its wireless data connection with first measuring device). Thus, after the first measuring device receives the connection request signal from the user device at step 8, the first measuring device then, at step 10, sends an acknowledgement signal back to the user device confirming the establishment of the connection.

[0055] Next, at step 12, the user device verifies that the connection with the first measuring device was successful. If the establishment of the connection between the user device and the first measuring device is not successful (i.e. if “No” at step 12, which may occur e.g. if the connection request signal at step 8 is not received by the first measuring device, or if the acknowledgement signal sent at 10 is not received by the user device), the user device returns to step 8. That is, the user device sends (another) connection request signal to the first measuring device to try (again) to establish a connection with the first measuring device. If, however, at step 12, the user device confirms that the establishment of its connection with the first measuring device is successful (i.e. if “Yes” at step 12), the user device proceeds to step 14 where the user device then sends a connection request signal to the next measuring device.

[0056] After sending the connection request signal to the next measuring device at step 14, the user device then waits for a connection with the next measuring device to be established (i.e. the user device awaits an acknowledgement signal from the next measuring device confirming the establishment of the connection with the next measuring device). Thus, after the next measuring device receives the connection request signal from the user device at step 14, the next measuring device then, at step 16, sends an acknowledgement signal back to the user device confirming the establishment of the connection.

[0057] At step 18, the user device verifies that the connection with the next measuring device was successful. If the establishment of a connection between the user device and the next measuring device is not successful (i.e. if “No” at step 18, which again may occur e.g. if the connection request signal at step 14 is not received by the next measuring device, or if theacknowledgement signal sent at 16 is not received by the user device), the user device returns to step 14. That is, the user device sends (another) connection request signal to the next measuring device to try (again) to establish a connection with the next measuring device. If, however, at step 18, the user device confirms that the establishment of its connection with the next measuring device is successful (i.e. if “Yes” at step 18), the user device proceeds to step20 where the user device detects / assesses (or it may prompt the user to indicate via the software / application running on the user device) whether there are any further (e.g. third or further) measuring devices to be added (i.e. that also need to establish a connection to the user device). If there are no further measuring devices to be added (i.e. no further measuring devices requiring connection to the user device, i.e. if “No” at step 20), the user device proceeds to step21 (discussed below). If, however, there is at least one further measuring device to be added at step 20, the user device returns to step 14, and steps 14-20 are then repeated for each additional measuring device that is to be added until all required measuring devices have been added (i.e. until a connection has been established between the user device and each one of the required measuring devices). In other words, steps 14-20 are repeated until the outcome at step 20 is “No” (i.e. indicating that all required measuring devices have established a connection with the user device and there are no further measuring devices requiring connection to the user device), whereupon the user device proceeds to step 21.

[0058] In step 21, the user device checks / verifies that there are at least two measuring devices connected to the user device. If this is not verified (i.e. if “No” at step 21 , indicating that there are fewer than two (i.e. one or zero) measuring devices connected to the user device), the user device again returns to step 14, and steps 14-21 are repeated until all required measuring devices have been added (i.e. until a connection has been established between the user device and each one of the required measuring devices) and the outcome at step 21 is “Yes”. Thereafter, the user device proceeds to stage 9.

[0059] Stage 9 is shown at the end / bottom in Figure 2, but it (stage 9) is also shown at the top / start in Figure 3. Both mean the same thing (i.e. stage 9 shown in Figure 2 and stage 9 shown in Figure 3 refer to the same stage of the process). However, the processes / steps that follow stage 9 are depicted in Figure 3, so these subsequent processes / steps will be described with reference to Figure 3.

[0060] Figure 3 has three columns (similar to Figure 2). Also, in Figure 3 (like in Figure 2) the column on the left represents the user device. However, importantly, the middle and righthand columns in Figure 3 are (i.e. what the middle and right-hand columns in Figure 3 refer to, or represent, is) not necessarily the same as in Figure 2.

[0061] For instance, as mentioned above, the middle column in Figure 2 represents a first measuring device, which is merely one out of the two or more measuring devices (and it may be the first one of the measuring devices to establish a data connection with the user device). However, in contrast to this, in Figure 3, the middle column relates to the master measuring device. The master measuring device (represented in Figure 3) may or may not be the same device that was the first measuring device (represented in Figure 2). In other words, sometimes, the particular measuring device that is chosen to be the master measuring device (or “master”) will be the same one (i.e. the very same device) that was the first measuring device. However, equally, it will also sometimes be the case that the particular measuring device that is chosen to be the master measuring device (master) will be one of the connected measuring devices other than the one that was the first measuring device. The selection of which one of the connected measuring devices is to serve as the master (and the reasons why a particular measuring device may be selected to be the master) will be discussed further below.

[0062] Similarly, the column on the right-hand side in Figure 3 does not necessarily refer to the same measuring device(s) as the one(s) that are represented in the right-hand side column in Figure 2. The right-hand column in Figure 2 represents the (or each of the) further measuring device(s), i.e. all of the other measuring devices that have established a connection with the user device other than the first measuring device, and these may be the measuring devices that established a data connection with the user device after the data connection between the user device and the initial / earliest (first) measuring device is established. However, in contrast, in Figure 3, the right-hand column represents the (or each of the) measuring device(s) which are designated as slave measuring device(s) (or “slave(s)"). The slave(s) are all of the measuring devices that are connected to the user device other than (i.e. except for) the one that is selected to be the master.

[0063] It may be that the timing for when acquisition of measurements / data is to commence (i.e. the time when measurements need to begin being taken and recorded by the multiple measuring devices concurrently (for subsequent transmission back to the user device) will be triggered by a particular event, or more specifically, by the detection of the particular event (the “trigger” or “trigger event”). For example, a trigger event might be if a voltage that is being monitored rises above a particular value / threshold (i.e. if it is desired to begin concurrent acquisition of data by the multiple measuring devices if / when the voltage being detected / monitored by a particular one of the measuring devices rises above the particular trigger threshold). In another example, a trigger event might be if / when the magnitude / amplitude of a current (or the current on a particular phase) being monitored exceeds a particular trigger threshold. In a further example, a trigger event might be if / when there is a desire to commencesampling and recording measurements from all of the devices upon a particular current phase state (e.g. a particular rising, or falling state) being detected on one of the phases, such that sampling is “triggered” (i.e. caused to commence by all of the measuring devices) upon this phase state being detected by the particular measuring device that is detecting / monitoring this parameter. In all of these example scenarios (and also in the many other examples that will also be readily apparent), the particular measuring device which is measuring the triggering parameter, or in other words, the particular measuring device which will be the one that detects the triggering event if / when it occurs, will generally be selected to be the master.

[0064] Alternatively, in some situations, the user may simply wish to selectively begin sampling at a particular user-initiated time. That is, the user may want to be able to cause the multiple measuring devices to begin acquiring measurements concurrently at a time of the user’s choosing, in which case, it may be that the measuring device chosen to be the “master” is the measuring device which is currently “selected” by / on the user device (so that the user can “trigger” the commencement of acquisition of measurements by the multiple measuring devices by causing / operating the user device to send a trigger signal to the master device from the user device at their desired time). Or, alternatively, the user could choose any of the connected measuring devices to be the “master”. (In this particular “user-initiated sampling” scenario, it may not matter which of the connected devices serves as the master).

[0065] Thus, if there is no particular reason why any one of the connected measuring devices should be assigned as (or preferred over all of the others to serve as) the master, it may simply be that the first measuring device (the one for which a connection to the user device was established earliest) is selected as the master, or (as above) the user may choose which measuring device is to be the master.

[0066] Returning Figure 3, recall (from above) that, upon reaching stage 9, respective data connections will have been established between the user device and each one of the two or more measuring devices. (However, at this point, none of the measuring devices have yet been assigned / designated as master or slave(s).) The next step after stage 9, i.e. after the establishment of the data connections between the user device and each one of the measuring devices, is step 22 where the user device sends a slave designation signal to all of the measuring device(s) except for the one which is to be designated as the master. This tells each one of those measuring device(s) that they have been designated as a slave. Thereafter, at step 24, each of the slave measuring device(s) commences continuous (i.e. periodic and repeating) sampling of measurements (i.e. each of the slave device(s) commences periodically taking measurements of the particular parameter(s) that it has been set to monitor / measure). However, the measurements / readings taken at this point by the slave device(s) may not be subsequentlyreported / transmitted to the user device (i.e. these (or some of these) initial readings may simply be taken and discarded if they do not need to be transmitted). “Acquisition” of readings (that is, identification of which of the repeated, periodic measurement / readings taken, and the subsequent transmission of these to the user device) by each slave device only commences for measurements / readings that are determined to have occurred after receipt of a “trigger” signal from the master measuring device (or after the time that the slave device determines the trigger event to have occurred, based on the trigger signal), as discussed below.

[0067] Importantly, for each slave device, at step 24 (which is after the slave device has received the slave designation signal sent to it by the user device), the slave device also commences listening / monitoring for synchronisation signals / packets from the master device, as discussed further below.

[0068] After the user device has, at step 22, sent the slave designation signal(s) to each one of the slave measuring device(s) (i.e. to each one of the connected measuring devices except for the one that is to be designated as the master), thereby causing those slave device(s) to commence continuous sampling while they await a trigger signal to commence actual acquisition (and also causing those slave device(s) to commence monitoring for synchronisation packets / signals from the master device), the user device meanwhile proceeds to step 26 where it sends a master designation signal to the one measuring device that has been (e.g. for reasons explained above) chosen to be the master measuring device. This master designation signal informs that particular (selected) measuring device that it has been designated as the master measuring device (master). The master designation signal sent by the user device to the master device (or possibly a subsequent / separate signal sent by the user device to the master device (not shown)) sends the “trigger” parameters, that is, informs the master device of what particular event it (the master device) must monitor for and which, if an occurrence of this specified event is detected, should cause the master device to: itself begin “acquiring” (i.e. begin recording / storing, for subsequent transmission) it’s periodic measurements of the parameter(s) that the master device is measuring, and send to each of the slave device(s) a trigger signal that they should also immediately begin acquiring (i.e. begin recording / storing, for subsequent transmission) their own respective periodic measurements of the parameter(s) that they are (i.e. that each slave device is) measuring.The master designation signal may also inform the master device of how long the “period of acquisition” should be (i.e. for how long, or for what period of time, acquisition of data shouldcontinue after the detection of the trigger event and the consequent commencement of acquisition of measurements), and the master designation signal may inform the master device of the sampling rate to be used by each of the measuring devices (the sampling rate may be set by the user device). The master device may also include this period of acquisition in the trigger signal it sends to each slave device upon the detection of the trigger event (so that, upon receiving the trigger signal and commencing acquisition of measurements, each slave device also knows how long to continue acquiring data for). The “period of acquisition” (i.e. how long acquisition of data should continue) may vary depending, for example, on what the trigger event is, what (and how much) information (including for what duration of time following a trigger event) the user requires measurements / data from each of the respective measuring devices, etc. The period of acquisition may therefore be user-definable, or there may be preset (or hardcoded) acquisition periods (durations) for different kinds of events (in which case the “period of acquisition” may not necessarily need to be signalled). Alternatively, the period of acquisition may initially be non-limited (or not set, and therefore not initially signalled by the user device to the master device, nor included in the trigger signals sent by the master device to each slave device), and it may be that acquisition is manually terminated (i.e. the period of acquisition is manually brought to an end) by the user manually causing this to be done via (i.e. by using controls on) the user device at a time of the user’s choosing. This may cause “termination of acquisition” signals (not shown) to be sent to all measuring devices by the user device, causing them to stop acquiring data. In a further alternative, the period of acquisition may (again) initially not be set (and therefore not initially signalled by the user device to the master device, nor included in the trigger signal sent by the master device to each slave device) but instead, the period of acquisition may be brought to an end upon the detection (by one or more of the measuring devices) of some predefined “termination event”, which may be signalled by the detecting device to all of the other measuring devices upon its occurrence / detection.

[0069] In any case, returning to Figure 3, as mentioned above, at step 26, the user device sends the master designation signal to the master device that is to be the master. Thereafter, at step 28, the master device commences continuous (i.e. periodic repeating) sampling of the particular parameter(s) that it has been set to monitor / measure. However, similar to the slave device(s) at step 24 (see above), the measurements / readings taken at this point (at step 28) by the master device are not recorded for subsequent reporting / transmission to the user device (i.e. these initial readings are not “acquired”). Rather, “acquisition” of readings by the master device only commences (i.e. the master measuring device only begins recording the measurement / readings it detects through its continuous (repeated periodic) sampling, for subsequent transmission to the user device) after the master measuring device detects the trigger event (and recall from above that master device is informed about what the triggerevent / should be in the “master designation signal” sent to it by the user device at step 26).

[0070] Importantly, for the master device, at step 28 (which is after the master device has received the master designation signal sent to it by the user device), the master device also commences broadcasting synchronisation signal / packets, or sending synchronisation signals / packets directly to each slave device, as discussed below.

[0071] Thus, after step 24 each of the slave device(s) are, and likewise after step 28 the master device is, continuously (i.e. periodically and repeating) sampling the parameters which each respective device is set to monitor / measure, but at this time (and prior to the detection of the trigger event) none of these devices are “acquiring” the measured data (i.e. none of them is recording the measurements taken at each sample time for subsequent transmission).

[0072] However, after step 28 the master device is also sending synchronisation signals / packets to the slave device(s), and after step 24 each of the slave device(s) is listening / monitoring for the synchronisation signals / packets from the master device. Possibilities (i.e. different options) for how this synchronisation signalling can be used for synchronising measurements obtained by the various (master and slave) measuring devices are discussed below. However, it is sufficient (at this point in the explanation) to note that, following step 28 (for the master device), and following step 24 (for each of the slave device(s)), and even before (but also after) the detection of the trigger event, the master device sends periodic synchronising signals / packets to each of the slave device(s) (or it broadcasts a synchronisation signal to all of the slave devices) for the purpose of synchronising (or allowing the synchronisation of) the measurements taken by each measuring device.

[0073] Referring again to Figure 3, the next step is when the master device detects the (predefined) trigger event. This is indicated as step 30 in Figure 3. As soon as the master device detects the occurrence of the predefined trigger event, the master device (as mentioned above): itself begins acquiring (i.e. it begins record ing / stori ng, for subsequent transmission) it’s own periodic measurements of the parameter(s) that the master device is measuring, and- sends to each one of the slave device(s) a trigger signal - the trigger signal sent to each slave device indicates that it should (also) immediately begin acquiring (i.e. begin recording / storing, for subsequent transmission) measurements of the parameter(s) that it is measuring, and that it (the slave device) should continue to do so for the “period of acquisition” (the duration of, or information about, which may also have been included in the trigger signal sent by the master device, as explained in more detail above).

[0074] At each slave device, the timing of receipt (by that slave device) of the “trigger signal” from the master device is adjusted factoring in transmit and receive delays.

[0075] Thus, upon the detection (by the master device) of the trigger event, all of the measuring devices which are connected to the user device commence (or in the case of the slave device(s), are caused to commence) acquiring data (i.e. they each commence acquiring measurements of the respective parameter(s) they are each measuring), and they all continue to do so until the “period of acquisition” ends / expires (or is brought to an end or terminated, e.g. manually by the user, or upon the detection of the predetermined “termination event”). The end of the “period of acquisition” is indicated in Figure 3 at step 32 (for the master device) and at step 34 (for each of the slave devices).

[0076] Next (i.e. after the “period of acquisition” ends and acquisition of measurements by the measuring devices consequently also ends), at step 36, the master device transmits to the user device all of the data / measurements acquired (i.e. sampled) by it during the period of acquisition. Similarly, at step 38 (which may or may not occur concurrently in time with step 36), each of the slave device(s) also transmits to the user device all of the data / measurements they (each) acquired (i.e. sampled) during the period of acquisition.

[0077] The measurement data thus received by the user device from each of the connected measuring devices (including the master device and all slave devices) can then be displayed on the screen of the user device, or used by the user device (or by the user or in some other way) for further computation or analysis (the results of which may be displayed on the screen of the user device).

[0078] Finally, after the transmission of the acquired measurement data by the (master and all slave) measuring devices (and reception thereof by the user device) is complete, the user device returns to state 3, and the measuring devices return to state 5. Thereafter, the processes described above with reference to Figures 2 and 3 can (if or when desired) be repeated or reperformed (possibly with different parameters, such as e.g. a differently defined trigger event and possibly a different measuring device selected as master, a different period of acquisition and / or sampling rate, different termination criteria, etc). Alternatively, the various measuring devices may simply be powered off and disconnected from whatever they are attached to / measuring, and the user device may also be powered off (or at least the application / software closed), and these various devices may be put into storage to be used in a different way, or in a different application, at a future time.

[0079] Referring again to Figure 3, it was mentioned above that, after step 28 the master device is (in addition to continuously sampling) also sending synchronisation signals / packets tothe slave device(s), and also that after step 24 each of the slave device(s) (in addition to also continuously sampling) is listening / monitoring for the synchronisation signals / packets from the master device.

[0080] A first synchronisation option, that is, a first option for how measurements / data acquired by the respective measuring devices may be synchronised, will now be explained.

[0081] Because each of the measuring devices, in addition to having the electronics and components required for measuring the particular parameter(s) that that device is able to measure, also has other necessary electronics too, including for instance, the electronics required to allow the measuring device to electronically store acquired measurements / data and also to communicate with the user device and other measuring devices wirelessly, therefore each measuring device necessarily also has its own (on-board, or on-the-device) processor, memory, communication equipment (such as e.g. antenna(s), modem), etc. The details of these various pieces of electronic equipment and components provided on (or which form part of) each measuring device are not relevant here and therefore will not be described further. However, it should be noted that the electronics associated with each measuring device operate such that each measuring device has its own clock, which is used to implement a counter on the device.

[0082] The counter on each measuring device increments (i.e. it increases in value by one) at a set frequency. This frequency is defined by (or related to) that device’s clock frequency. However, it is very important to note that there can be slight differences or variation in the clock frequency as between different measuring devices. In other words, the clock frequency of one measuring device may not be (and often / typically it is not) exactly identical to the clock frequency of another (or any other) measuring device. This can lead to “drift” in the clock of one measuring device relative to the clock of another measuring device over time, and this is another factor that creates a need for synchronisation between different measuring devices.

[0083] In any case, for each measuring device, when the value of the counter reaches a predefined value (hereafter this predefined value will be referred to as COUNTERVAL), this causes the measuring device to sample (i.e. to take a measurement) and the counter resets to zero. The device’s counter value then increments to one at the next counter cycle, and to two at the next counter cycle, etc, until the value of the device’s counter again reaches COUNTERVAL whereupon the measuring device is (again) caused to take a sample and reset, and the process repeats.

[0084] Therefore, for each measuring device, the counter frequency and the value assigned as COUNTERVAL sets the period and moment of sampling for that measuring device.

[0085] In this “first synchronisation option”, the value of COUNTERVAL is the same in all of the connected measuring devices, i.e. in this “first synchronisation option”, the predefined value of COUNTERVAL is the same integer number for all of the measuring devices connected to the user device.

[0086] In this “first synchronisation option”, to enable synchronisation, following step 28 in Figure 3, the master measuring device periodically (and repeatedly) transmits synchronisation signals 40 to each of the slave device(s). The synchronisation signals 40 contain (i.e. the synchronisation signal 40, on each occasion it is sent, contains) the master device’s current counter value (i.e. the “master counter value”). This (each) synchronisation signal 40 containing the master device’s current “master counter value” may be transmitted to all of the slave device(s) via common broadcast (i.e. as a common signal received by all slave devices), or it may be transmitted directly as separate transmissions / signals addressed to each respective slave device. The transmission latency associated with the transmission of the (each) synchronisation signal 40 (containing the “master control value”) to each of the slave devices is fairly controlled and predictable.

[0087] In this “first synchronisation option”, each slave device receives each transmitted synchronisation signal 40 (including the current “master counter value” contained therein) and performs a calculation to determine the delay in receiving the signal. The receive latency associated with the reception of each synchronisation signal 40 (each containing the current “master control value”) by each slave device is also fairly controlled and predictable.

[0088] Each slave device then updates its own (slave) counter value to match (i.e. to make it the same as) the master counter value in real-time. The received master counter value is also modified using the calculated transmit and receive delay to determine the actual master counter value at the time (in real-time). Accordingly, in this “first synchronisation option”, the master and slave counter values are always maintained in synchronisation, meaning that each device samples (i.e. each device takes a measurement) at the same time.

[0089] This, in turn, causes the data obtained by each of the respective (master and all slave) measuring devices to be “inherently” synchronised. The reason is because, by ensuring that each device “samples” (i.e. takes each successive measurement) at (or very close to) the same moment in time, consequently when the measurements acquired (i.e. the samples taken and stored) by each of the respective measuring devices are later transmitted to the user device to be displayed (or for other computation or analysis), the measurements obtained by each of the respective measuring devices are already inherently “aligned in time” with all of the others when they are received by the user device (and this is true even if the measurements fromdifferent measuring devices are received by the user device at different times).

[0090] In this “first synchronisation option”, for a given slave device, the period between when (or in other words the frequency at which) the master device sends synchronisation signals 40 to that slave device (containing the master device’s “master counter value”) may be calculated taking into account a worst-case clock drift between the master and that slave device and to maintain synchronisation therebetween within a determined period.

[0091] Also, as mentioned above, for each slave device, the timing of receipt (by that slave device) of the “trigger signal” from the master device is adjusted factoring in transmit and receive delays. This further helps to ensure that all samples / measurements obtained (i.e. “acquired”) by all measuring devices during the “period of acquisition” occur simultaneously (or at least close to simultaneously).

[0092] A second synchronisation option, that is, a second possible option for how measurements / data acquired by the respective measuring devices may be synchronised, will now be explained. This second synchronisation option, in effect, involves implementing what is sometimes referred to as a phase locked loop scheme.

[0093] In the “second synchronisation option”, although the value of COUNTERVAL may initially be the same in all of the connected measuring devices (although this also may not be the case), in any event, in the second synchronisation option the value of COUNTERVAL in the slave devices may be caused to change (i.e. caused to become different) to the value of COUNTERVAL used by the master, and in fact, the value of COUNTERVAL used by each of the slave devices may be periodically and / or repeatedly changed / updated.

[0094] In the “second synchronisation option”, to enable synchronisation, following step 28 in Figure 3, the master measuring device (again) periodically (and repeatedly) transmits synchronisation signals 40 to each of the slave device(s), but in this (“second”) synchronisation option, in each synchronisation signal 40 sent to each slave device, the master device will, if required, instruct the slave device to change its value of COUNTERVAL (i.e. to increase or decrease the value of COUNTERVAL by a certain amount), and this necessarily causes the slave device to change the counter value at which, and hence the times at which, it takes samples and resets its counter.2This is therefore used to adjust the timing of when that slave2Typically, if the master counter value is higher than that of the slave, then the slave COUTNERVAL is lowered by some proportional amount in order for the slave to reduce its sampling period (or in other words to increase sampling frequency) and therefore sample sooner. Alternatively, if the master counter value is lower than that of the slave, then the slave's COUNTERVAL is increased by a proportional amount to increase its sampling period (or in other words to decrease its sampling frequency) and therefore sample later. When the master and slave counter values are the same, do nothing. In this way the slave sample clock locks in with the master. Thedevice “samples” thereby maintaining the timing of sampling by the slave device in (at least fairly close) synchronisation with the timing of the sampling performed by the master device, and this therefore helps to compensate for clock drift between the master and that slave device, thereby maintaining (at least fairly close) synchronisation between them. This is done separately / individually for each slave device. In other words, all of the various slave devices will not necessarily all have their value of COUNTERVAL changed by the master device in the same way (or by the same amount) at the same time. Rather, the amount by which the value of COUNTERVAL used by each slave device is updated at a given time (if this is required at all at the given occasion / instant) will be different as between the different slave devices. This is necessary in order to compensate for the clock drift in each slave device, each of which will drift differently (i.e. at a different rate) relative to the master device.

[0095] Accordingly, in this “second synchronisation option”, the timing of sampling by each slave device is maintained in (at least fairly close) synchronisation with the timing of the sampling by the master device. The result is that, somewhat similar to the first synchronisation option (although achieved in a somewhat different way), in the second synchronisation option, each device again samples (i.e. each device takes measurements) at the same time (or close to the same time).

[0096] This, in turn, causes (like it did for the first synchronisation option) the data obtained by each of the respective (master and all slave) measuring devices to be “inherently” synchronised. The reason is because, by ensuring that each device “samples” (i.e. takes each successive measurement) at (or very close to) the same moment in time, consequently when the measurements acquired (i.e. the samples taken and stored) by each of the respective measuring devices are later transmitted to the user device to be displayed (or for use in other computation or analysis), the measurements obtained by each of the respective measuring devices are already inherently “aligned in time” with all of the others when they are received by the user device (and this is true even if the measurements from different measuring devices are received by the user device at different times).

[0097] A third synchronisation option for allowing measurements / data acquired by the respective measuring devices to be synchronised will now be explained.

[0098] This third synchronisation differs from the first and second synchronisation options discussed above in that, whereas those (first and second) synchronisation options both caused adjustments to the slave COUNTERVAL do not necessarily have to be adjusted by a proportional amount. Other, non-linear, adjustments can also be made, and no particular limitation applies to the way in which the adjustments are calculated.the data obtained by the respective (master and all slave) measuring devices to be “inherently” synchronised, this third synchronisation option does not. Nevertheless, this third synchronisation option does still allow the measurement data obtained by each of the respective measuring devices to be synchronised, albeit subsequently (i.e. the sets of measurement data received from each of the respective measuring devices may need to be “aligned in time” by the user device after all of the sets of measurement data (from all of the respective measuring devices) have been received by the user device.

[0099] In this third synchronisation option, no changes are made to the clock counters of, or to the value of COUNTERVAL used (from time to time) by, the respective measuring devices. Instead, following step 28 in Figure 3, in at least one synchronisation signal 40 sent to each slave device, the master device will include data about a particular event (or set of events) it has detected or about a particular measurement (or set of amendments) it has taken, and importantly, the synchronisation signals 40 sent to the slaves will also include information about the timing of when the said event(s) or measurement(s) were detected / taken by the master device (and the master device itself also records this time information). When this signal 40 (containing this information about the event(s) / measurement(s) detected / taken by the master device including the timing thereof at the master device) is received by each slave device, and after the slave device adjusts for the transmission and reception delay associated with the signal 40, the slave device can therefore determine the time (according to the slave device’s own clock / counter) when the event(s) / measurement(s) were detected / taken by the master device. This, therefore, allows the slave device to identify the particular measurement(s) that it was taking (or took) at the same moment in time. This therefore allows the slave device to effectively “event-stamp” the particular measurement(s) that it was taking at the same time when the master device was detecting / taking the event(s) / measurement(s) about which the master device included information in the signal 40. This “event-stamp” information can then be included (and saved / stored) as part of the data that is “acquired” by the slave device for later transmission to the user device. Furthermore, by causing all of the slave devices to do this, when the sets of data from the respective slave devices (and the master device) are subsequently received by the user device (after the period of acquisition has ended and the data has been transmitted), even though the various sets of data sent by the respective different measuring devices will not be “inherently” synchronised (i.e. they will not be inherently aligned in time already upon receipt by the user device), nevertheless the data received from each slave device will contain “eventstamp” information which, together with the timing information recorded by the master device, can be used e.g. by the user device (or some other device or in some other way), to align the data received from each slave device in time with the data received from the master device as a subsequent processing step.

[0100] A fourth synchronisation option, that is, a fourth possible option for how to cause measurements / data acquired by the respective measuring devices to be synchronised involves maintaining synchronisation of the clocks of the respective (individual) measuring devices. There are a range of methods that have been developed and which could potentially be used to achieve this. One such method (albeit not necessarily the only one) is the Precision Time Protocol (PTP) defined in IEEE 1588 standard. The details of PTP (and how it works) may be found in the standard and therefore need not be explained here. At its heart, PTP provides an accurate method for calculating the transmit (Tx) and receive (Rx) delays by averaging round trips. It can be used to adjust counter synchronisation, or trigger synchronisation, or (as in the present fourth synchronisation option), device clock. In any case, as just stated, PTP is only one possible option from among a range of methods that exist which could be used to maintain synchronisation of the clocks of the respective measuring devices.

[0101] The reason maintaining synchronisation of the clocks of the respective measuring devices helps to maintain synchronisation of the measurement data obtained by those respective devices is because, if the clocks of the respective devices are synchronised, and provided one or more signals of some form is / are sent allowing all measuring devices to “timestamp” or “event-stamp” their data, then it is possible (a simple matter) for the “timestamp” or “event-stamp” information included in the data from all devices to subsequently be used to (after it has been transmitted to the user device) to align the data from all devices in time.

[0102] It should be noted that, in the explanations given above, the wireless communications between measuring devices will typically be achieved by radiofrequency (RF) communication (i.e. via signals sent using electromagnetic radiation in the “radio” frequency). However, other methods for wireless communication between the measuring devices could also be used, for example, transmissions using EM radiation of other frequencies (i.e. other than frequencies in the “radio” band) including e.g. using visible light, or infrared, etc. Other possible modes of wireless communication (which do not require the use of electromagnetic radiation as a signal carrier) could also be used, including e.g. using sound as a signal carrier.

[0103] It should also be noted that many of the explanations provided above in the Detailed Description section make reference to systems with so-called “master slave” topologies; that is, to systems in which, for the purpose of synchronisation between measuring devices, one of the measuring devices is designated as master and the other(s) as slave(s). However, it is to be understood that the invention is not necessarily limited to (and it does not require) the use of a “master slave” topology for synchronisation. Other system topologies could also be used for synchronisation between measuring devices, such as so-called “hub and spoke”, “ring” and “mesh” topologies. Thus, any system topology may be used for synchronisation provided thesignals used for synchronisation are able to propagate through the multiple devices on the network in a deterministic way (or, in other words, in a way that the transmit and receive delays associated with signal transmission are able to be estimated / calculated and adjusted for).

[0104] In this specification, the term “comprising” is (and likewise variants of the term such as “comprise” or “comprises” are) intended to denote the inclusion of a stated integer or integers, but not necessarily the exclusion of any other integer, depending on the context in which the term is used.

[0105] It is to be understood that the invention is not necessarily limited to or by any specific features (or anything else) described in the Brief Description of the Figures or Detailed Description or shown in the Figures. The invention is, therefore, claimed in any of its forms or modifications within the scope of the appended claims as properly interpreted.

[0106] It is also to be clearly understood that mere reference in this specification to any previous or existing devices, apparatus, products, systems, methods, practices, techniques, publications, patents, or indeed to any other information, or to any problems or issues, does not constitute an acknowledgement or admission that any of those things, whether individually or in any combination, formed part of the common general knowledge of those skilled in the field or is admissible prior art.

Claims

CLAIMS1. A method for synchronisation of measurement data obtained and transmitted to a user device by two or more respective electrical parameter measuring devices that obtain measurements concurrently, wherein each measuring device can communicate wirelessly with other measuring devices and at least one of the measuring devices is a contactless measuring device, and in the method at least while the measuring devices are concurrently obtaining measurements, one or more signals are transmitted between the measuring devices, and time-related information associated with the one or more signals transmitted between measuring devices is used to synchronise measurement data obtained by each of the respective measuring devices, or to allow measurement data obtained by each of the respective measuring devices to be synchronised.

2. The method as claimed in claim 1 , wherein measurement data obtained by the two or more measuring devices concurrently is transmitted to the user device via Bluetooth.

3. The method as claimed in any preceding claim, wherein each measuring device can communicate with other measuring devices via radiofrequency (RF) communication.

4. The method as claimed in any preceding claim, wherein, prior to commencing acquisition of measurements concurrently, each measuring device establishes a wireless connection with the user device.

5. The method as claimed in any preceding claim, wherein, prior to commencing acquisition of measurements concurrently, one measuring device is designated to operate as a master measuring device and the other measuring device(s) is / are designated to operate as slave measuring device(s).

6. The method as claimed in any preceding claim, wherein the acquisition of measurements concurrently by the two or more measuring devices commences upon the occurrence of a trigger event.

7. The method as claimed in claim 6, wherein the two or more measuring devices commence sampling prior to the commencement of the concurrent acquisition of measurements.

8. The method as claimed in claim 6 or 7, wherein the trigger event is a predetermined event that, if or when it occurs, is able to be detected by one of the measuring devices.

9. The method as claimed in claim 8, wherein the measuring device that is able to detect the predetermined trigger event is designated as a master measuring device, and the other measuring device(s) are designated as slave measuring device(s), and upon the detection by the master measuring device of the predetermined trigger event occurring, the master measuring device commences acquiring measurements of the parameter(s) it is measuring and it transmits a trigger signal to each other (slave) measuring device causing each of them to concurrently commence acquiring measurements of the parameter(s) they are each measuring.

10. The method as claimed in claim 9, wherein the trigger signal, or alternatively some other signal sent to each measuring device, informs each measuring device of one or both of: how long it should continue acquiring measurements for following the commencement of acquisition of measurements, and the sampling rate to be used by each measuring device.

11. The method as claimed in any preceding claim, wherein, after completion of the concurrent acquisition of measurements by the two or more measuring devices, each measuring device transmits measurements it acquired to the user device.

12. The method as claimed in claim 11 , wherein measurement data received by the user device from the two or more measuring devices is caused to be synchronised by causing the timing of the sampling by each respective measuring device to be synchronised.

13. The method as claimed in claim 11 , wherein measurement data received by the user device from the two or more measuring devices is caused to be synchronised by causing the timing of the sampling by each respective measuring device, and the period of (concurrent) acquisition for each measuring device, to be synchronised.

14. The method as claimed in any preceding claim, wherein each measuring device has a counter which increments (or decrements) at each cycle of the counter, and when the value of the counter reaches a predefined value (COUNTERVAL) the measuring device is caused to sample and reset the value of the counter.

15. The method as claimed in claim 14, wherein one measuring device (the master measuring device) periodically transmits synchronisation signals to each other (slave) measuring device, wherein each synchronisation signal sent to each slave measuring device contains the current value of the counter of the master measuring device, and upon receipt of a synchronisation signal each slave measuring device updates / changes the current value of its own counter to match the current value of the counter of the master measuring device.

16. The method as claimed in claim 14, when one measuring device (the master measuring device) periodically transmits synchronisation signals to each other (slave) measuring device, wherein each synchronisation signal sent to each slave measuring device instructs the slave measuring device to (if necessary) change its predefined value (COUNTERVAL) to synchronise the timing of when the slave measuring device samples with the timing of when the master measuring device samples.

17. The method as claimed in any preceding claim, wherein there is a clock associated with each measuring device, and measurement data received by the user device from the two or more measuring devices is caused to be synchronised by causing the clocks associated with each of the measuring devices to remain synchronised, and the clock data is used to:- timestamp data to allow information included in the data from all devices to subsequently be used to align the data from all devices in time, and / or- synchronise sampling by the measuring devices.

18. The method as claimed in any preceding claim, wherein one measuring device transmits (or causes to be transmitted) at least one synchronisation signal to each other measuring device, which includes data about a particular event (or set of events) that the said one measuring device has detected, or about a particular measurement (or set of amendments) the said one measuring device has taken, the synchronisation signal also includes information about the timing of when the said event(s) or measurement(s) were detected / taken by the said one measuring device,and the said one measuring device itself also records this time information, and when the synchronisation signal is received by each other measuring device, each of the said other measuring devices can determine the time (according to a clock / counter of the said other device itself) when the event(s) / measurement(s) were detected / taken by the said one device.

19. The method as claimed in claim 18, wherein each said other measuring device identifies the particular measurement(s) that it was taking (or took) at the time when the event(s) / measurement(s) were detected / taken by the said one measuring device, and the said other measuring device “event-stamps” the particular measurement(s) that it took at the time when the said one measuring device was detecting / taking the event(s) / measurement(s) about which the said one measuring device included information in the synchronisation signal.

20. The method as claimed in claim 19, where the “event-stamp” information is included in the data that is “acquired” by each said other measuring device for later transmission to the user device.

21. The method as claimed in claim 20, wherein, after the data from the one or more respective other measuring devices, and from the said one measuring device, are received by the user device, the “event-stamp” information contained in the data from each said other measuring device, together with the timing information recorded by the said one measuring device, can be used to align the data received from each said other measuring device in time with the data received from the said one measuring device.

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