Patent Description:
A mechanical seal is a device configured to provide a sealing interface between a static housing and rotating shaft of a device, such as a pump, mixer or the like, for the purpose of inhibiting fluid within the device from escaping and/or external contaminants from entering the device. Mechanical seals are employed in a wide variety of industrial applications, processing media and operating conditions, where a gap between a rotating shaft and a static housing has to be sealed.

Referring to <FIG>, a cross-sectional view of a mechanical seal <NUM> of the prior art is depicted. In this depiction, the mechanical seal <NUM> is configured to inhibit the flow of fluid and contaminants through a gap <NUM> between a stationary housing <NUM> and a rotating shaft <NUM>. The mechanical seal <NUM> is generally comprised of an annular stationary ring <NUM> (also known as a primary ring) and annular rotating ring <NUM> (also known as a mating ring), a pair of seals or glands <NUM>, <NUM> (which are generally, but certainly not limited to, elastomeric sealing elements such as O-rings), and a biasing member <NUM>. While the mechanical seal <NUM> depicted in <FIG> comprises a single pair of sealing rings <NUM> and <NUM>, it will be understood that mechanical seals can comprise additional sealing interfaces.

In operation, the annular stationary ring <NUM> remains fixed in position relative to the housing <NUM>. Gland <NUM><NUM> is positioned between the annular stationary ring <NUM> and the housing <NUM> to inhibit the flow of fluid between these components. Annular rotating ring <NUM> rotates with the rotating shaft <NUM>. Gland <NUM> is positioned between the annular rotating ring <NUM> and the rotating shaft <NUM> to inhibit the flow of fluid between these components.

Both the annular stationary ring <NUM> and the annular rotating ring <NUM><NUM> include smooth, contacting seal faces <NUM>, <NUM>, thereby forming a sliding seal interface <NUM>. Accordingly, use of the mechanical seal <NUM> enables the radial gap <NUM>- where fluid would normally escape - to be sealed by a flat, sliding seal interface <NUM> that is perpendicular to the rotating shaft <NUM>, and therefore much easier to seal. A biasing member <NUM>, such as one or more coil springs and/or a bellows arrangement, can be positioned between a boss <NUM> on the rotating shaft <NUM> and the gland <NUM> and/or annular rotating ring <NUM> to urge the floating annular rotating ring <NUM> towards the annular stationary ring <NUM>. In this manner, the biasing member <NUM> aids in maintaining contact between contact seal faces <NUM>, <NUM> by accommodating small shaft deflections, shaft movement due to bearing tolerances and out of perpendicular alignment due to manufacturing tolerances.

Because annular rotating ring <NUM> rotates relative to annular stationary ring <NUM>, there is naturally some wear on the seal faces <NUM>, <NUM> during operation. In particular, wear of the sliding seal interface <NUM> can be accelerated in the presence of friction and heat generation, in particular if loading of the components and/or friction is increasing. Excessive wear of the seal faces <NUM>, <NUM> ultimately leads to failure of the mechanical seal <NUM>.

To slow the rate of wear, often a lubricant, commonly referred to as a lubricating fluid or barrier fluid, is introduced into the seal interface <NUM>. The lubricating fluid can be the fluid to be sealed, or it can be another barrier fluid introduced into the seal interface <NUM>. In another example, the seal interface can be lubricated by a dry gas, such as a vapour of the sealed product, air or nitrogen.

More advanced mechanical seal systems can include multiple mechanical seals, such as a dual or double mechanical seal. Such mechanical seal systems can be provided with more than a single lubricating fluid. For example, in some double seal systems, the first mechanical seal is lubricated by a vapour of the sealed product, and the second mechanical seal is lubricated with another liquid or gas compatible with the sealed product. In some cases, the lubricating fluid of the second mechanical seal can be maintained at a higher pressure to further minimize leaking of the sealed product to the atmosphere.

As with all mechanical systems, eventually the annular stationary ring <NUM> and the annual rotating ring <NUM> will wear out and need to be replaced. In some cases, the components of the mechanical seal <NUM> will simply reach the end of their useful life. In other cases, certain conditions will hasten wear on the components within the mechanical seal <NUM>. Some of these conditions include mis-installation of seal components or improper seal selection, the seal faces opening during operation as a result of axial misalignment or improper loading, flashing (liquid to vapour transition that causes pulsating leakage and chatter of the seal), cavitation, or environmental conditions which can lead to a collapse of the thin film of lubricant.

Efficient operation and maintenance of rotating or reciprocating equipment is essential to maximize production capacity and minimize downtime. Moreover, unexpected catastrophic equipment failure can result in injury to personnel. Fortunately, in many cases the mechanical seal system will begin to show signs of distress in advance of a catastrophic failure, and in some cases indicate the remaining useful life of the components.

Acoustic emission sensors have been used in relation to rotating equipment and machinery to determine component failure and detect signs of distress in advance of catastrophic failure, for example as described in <CIT>. Advantages of using acoustic emission sensors are that they are non-intrusive and enable real-time monitoring of the system, enabling monitoring in situ.

However, use of such acoustic emission sensors requires careful placement of the acoustic emission sensors to ensure that audible acoustic emissions are detected from the components of the system that need to be monitored. In many cases the acoustic emission sensors cannot be placed at the desired locations close to the seal but instead need to be placed at some distance away on the machinery casing, where the sound consequently has to pass several component interfaces that limit the ability to detect the signal.

<CIT> describes a monitoring system for a wind turbine includes at least one acoustic sensor configured to measure an acoustic emission generated by at least one component of the wind turbine, and a control system configured to calculate at least one wear characteristic of the component based on the measured acoustic emission. The wear characteristic includes at least one of a current amount of wear on the component, a rate of wear on the component, and a predicted amount of wear on the component.

<CIT> describes an acoustic measurement system for an industrial process asset that includes a process measurement device providing a value representative of an acoustic signal near the industrial process asset based in part on a signal from an acoustic sensor positioned near the industrial process asset.

<CIT> describes a method for monitoring the condition of a mechanical seal in an apparatus provided with a rotating part, where in a pump which has a rotating shaft for the forwarding of a fluid, the sound emission of the seal is continually measured at discrete times in the operating state of the apparatus and at least one statistical characteristic value is won from the acoustic signals.

Aspects of the invention are as set out in the independent claims and optional features are set out in the dependent claims. Aspects of the invention may be provided in conjunction with each other and features of one aspect may be applied to other aspects.

In a first aspect of the disclosure there is provided a system comprising a condition monitoring apparatus, the system comprising rotating or reciprocating machinery and a seal. The apparatus comprises a first acoustic sensor coupled proximate to the seal for providing a first acoustic emission signal, a second acoustic sensor coupled proximate to the rotating or reciprocating machinery for providing a second acoustic emission signal, and a filter module. The filter module is configured to perform active noise cancellation based on a comparison of the first acoustic emission signal and the second acoustic emission signal.

Advantageously such a condition monitoring apparatus means that the placement of the acoustic emission sensors does not need to be so exact - instead there is more flexibility in the placement of the sensors as the apparatus is better suited to deal with the noise generated by the system and component interfaces.

It will be understood that the rotating or reciprocating machinery may comprise a pump, mixer or compressor. The seal may comprise a mechanical seal such as a dry gas seal. In the context of the present disclosure, if will be understood that when an acoustic emission sensor is described as being coupled to the machinery or seal that it means that the acoustic emission sensor is coupled to the machinery or seal in such a way that it can received acoustic signals from the machinery or seal.

The apparatus may be configured to reduce the bandwidth of the first acoustic emission signal and the second acoustic emission signal. For example, the filter module may be configured to reduce the bandwidth of the first acoustic emission signal and/or the second acoustic emission signal, or another module such as a bandwidth reduction module may be configured to reduce the bandwidth of the first acoustic emission signal and/or the second acoustic emission signal. For example, the bandwidth reduction may be performed locally to the machinery and seal whereas the active noise cancellation may be performed remotely to the machinery and seal.

Converting a high bandwidth signal to a lower bandwidth signal and then performing active noise cancellation on that lower bandwidth signal means that cheaper/off-the-shelf components can be used to perform the noise cancellation. In addition, the lower bandwidth signal may result in energy savings as less data may need to be transmitted, which also reduces the computational burden in determining the condition of the system. As an example, a higher bandwidth signal (for example, as received by the acoustic emission sensors) may be in the range of <NUM> to <NUM>, whereas the lower bandwidth signal (to which the higher bandwidth signal is reduced) may be in the range of <NUM> - <NUM>. Transmitting and processing less data may also reduce battery consumption (if a battery is being used), meaning that the condition monitoring system may be left longer between service/maintenance intervals.

In some examples the apparatus is configured to reduce the number of samples of the first acoustic emission signal and the second acoustic emission signal. For example, the filter module may be configured to downsample the first acoustic emission signal and/or the second acoustic emission signal, or another module such as a downsampling module may be configured to downsample the first acoustic emission signal and/or the second acoustic emission signal. For example, the downsampling may be performed locally to the machinery and seal whereas the active noise cancellation may be performed remotely to the machinery and seal.

As with reducing the bandwidth of the signal, downsampling means that cheaper/off-the-shelf components can be used to perform the noise cancellation. In addition, the downsampled signal may result in energy savings as less data may need to be transmitted, which also reduces the computational burden in determining the condition of the system. Transmitting and processing less data may also reduce battery consumption (if a battery is being used), meaning that the condition monitoring system may be left longer between service/maintenance intervals.

In some examples the apparatus is configured to amplify the first acoustic emission signal and the second acoustic emission signal. For example, the filter module may be configured to amplify the first acoustic emission signal and the second acoustic emission signal. Additionally or alternatively each sensor may comprise an amplifier configured to locally amplify the output from its corresponding sensor prior to the signal being sent to the filter module.

The condition monitoring apparatus may be configured to obtain at least one of:.

The filter module may be configured to perform active noise cancellation based on a comparison of at least one of:.

For example, active noise cancellation may comprise inverting the phase of the original signal (also known as antiphase) with a signal of the same amplitude but inverted. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out - an effect which is called phase cancellation.

The RMS and/or envelope signals may be obtained by the filter module - for example the filter module may be configured to process signals received from the first acoustic emission sensor and the second acoustic emission sensor to produce respective RMS and envelope signals. Additionally or alternatively, the apparatus may comprise respective RMS and enveloping modules configured to process signals received from the first acoustic emission sensor and the second acoustic emission sensor to produce respective RMS and envelope signals.

In some examples the envelope signal may be acquired via an analogue circuit, for example using a Schottky diode circuit, optionally with a low pass filter. In some examples the RMS may be obtained via a digital circuit, for example using an AD8456 chip.

The filter module may be configured to perform active noise cancellation based on a comparison of both (i) the first RMS signal and the second RMS signal, and (ii) the first envelope signal and the second envelope signal.

The comparison may comprise a mathematical operation between the first RMS signal and the second RMS signal, and a mathematical operation between the first envelope signal and the second envelope signal. For example, the mathematical operation may comprise a subtraction between the first RMS signal and the second RMS signal, and a subtraction between the first envelope signal and the second envelope signal. In some examples the mathematical operation comprises combining the first RMS signal and the second RMS signal, optional by the inverting the phase of one signal (e.g. by <NUM> degrees) relative to the other. In this way, the first RMS signal and the second RMS signal may cancel each other out when added together and when <NUM> degrees out of phase from each other.

In some examples the filter module is configured to rectify the first acoustic emission signal prior to obtaining the first envelope signal, and rectify the second acoustic emission signal prior to obtaining the second envelope signal.

It will be understood that in some examples the apparatus may be configured to communicate with a diagnostic module, or may comprise a diagnostic module. In such examples the filter module may be configured to output a noise-cancelled signal to the diagnostic module for determining the condition of the system. The noise cancelled signal may comprise at least one of (i) an RMS noise-cancelled signal and (ii) an envelope noise-cancelled signal. In some examples the diagnostic module is physically coupled to the system comprising the rotating or reciprocating machinery and the seal (and in some examples the diagnostic module may comprise the filter module), but in other examples the diagnostic module is remote from the system comprising the rotating or reciprocating machinery and the seal - for example the filter module may comprise a communications interface to communicate with the diagnostics module.

In another aspect of the disclosure there is provided a method of monitoring the condition of a system comprising rotating or reciprocating machinery and a seal. The method comprises obtaining first acoustic emission data emitted from the seal, obtaining second acoustic emission data emitted from the pump, and performing active noise cancellation based on a comparison of the first acoustic emission data and the second acoustic emission data.

The method may comprise reducing the bandwidth of the first acoustic emission data and/or the second acoustic emission data prior to performing active noise cancellation. Additionally or alternatively the method may further comprise reducing the number of samples of the first acoustic emission data and the second acoustic emission data.

In some examples the method further comprises obtaining:.

The method may comprise performing active noise cancellation based on a comparison of at least one of:.

In some examples the method further comprises performing active noise cancellation based on a comparison of both (i) the first RMS signal and the second RMS signal, and (ii) the first envelope signal and the second envelope signal. The comparison may comprise, for example, a mathematical operation between the first RMS signal and the second RMS signal, and a mathematical operation between the first envelope signal and the second envelope signal. For example, the mathematical operation may be a subtraction.

The method may further comprise rectifying the first acoustic emission signal prior to obtaining the first envelope signal, and rectifying the second acoustic emission signal prior to obtaining the second envelope signal.

In some examples the method comprises outputting a noise-cancelled signal, and determining a condition of the system based on the noise-cancelled signal. It will be understood that the noise-cancelled signal may comprise at least one of (i) an RMS noise-cancelled signal and (ii) an envelope noise-cancelled signal. In some examples the method comprises transmitting the noise-cancelled signal to a remote device via a communications interface for determining a condition of the system.

Determining a condition of the system may comprise:.

In another aspect there is provided a computer readable non-transitory storage medium comprising a program for a computer configured to cause a processor to perform the method of monitoring the condition of a system comprising rotating or reciprocating machinery and a seal as described above.

Embodiments of the disclosure relate to a condition monitoring apparatus for a system comprising rotating or reciprocating machinery (such as a pump) and a seal. In general terms, the condition monitoring system, receives acoustic emission signals or data from respective acoustic emission sensors, and performs active noise cancellation based on a comparison of the two signals or data. Advantageously, by performing noise cancellation in this manner, the placement of the acoustic emission sensors relative to the seal and the rotating or reciprocating machinery does not need to be so precise, as the noise cancellation can remove noise from the acoustic signals or data that may be performed by other components and component interfaces in the vicinity of the seal and rotating or reciprocating machinery.

Additionally, embodiments of the disclosure also optionally downsample and/or reduce the bandwidth of the acoustic emission signals or data prior to the active noise cancellation being performed. Advantageously this may mean that the volume of data being sent to the noise cancellation circuitry can be reduced. This may mean that cheaper, off the shelf, components can be used to perform noise cancellation. It also means that less data is being processed, which can reduce computational burden and reduce energy consumption. This may be particularly relevant if analysis of the data output from the condition monitoring system is transmitted elsewhere (for example, wirelessly) for processing remotely (such as in the cloud or on a remote device/controller).

<FIG> depicts a functional schematic block diagram of an illustrative condition monitoring apparatus <NUM> that may facilitate establishing and/or determining seal conditions for seals and/or other suitable seal systems (for example, operating conditions for a seal, operational conditions for a seal interface, etc.) and/or machinery involving a rotating or reciprocating assembly, such as a pump, mixer or compressor. The seal monitoring system <NUM> may include and/or may be configured to monitor a seal interface of a dry gas seal disposed between a rotatable shaft and a stationary housing, or it may, for example, involve a liquid lubricated seal, for example the mechanical seal as shown in <FIG>. Indeed it will be understood that embodiments of the disclosure may be configured to provide a condition monitoring apparatus for mechanical seals (gas seals or liquid lubricated seals) and/or bearings, each of which may emit different acoustic traces or resonances.

The example condition monitoring system <NUM> shown in <FIG> comprises respective acoustic emission sensors <NUM>, <NUM>, for respectively coupling proximate to the seal and the pump.

In some cases, at least one of the acoustic emission sensors <NUM>, <NUM> may be coupled relative to and/or otherwise stationary relative to a stator portion of the seal and, in some cases, may be formed as part of the stator portion of the seal. Alternatively or in addition, at least one of the acoustic emission sensors <NUM>, <NUM> may be secured relative to a housing component of a system to which the seal is applied and/or may be remote from the seal and/or the system to which the seal is applied. In some examples the condition monitoring system <NUM> as a whole may be coupled relative to and/or otherwise stationary relative to a stator portion of the seal and, in some cases, may be formed as part of the stator portion of the seal. Alternatively or in addition, at least a portion of the condition monitoring system <NUM> may be secured relative to a housing component of a system to which the seal is applied and/or may be remote from the seal and/or the system to which the seal is applied.

The acoustic emission sensors <NUM>, <NUM> may be piezo-electric transducers configured to convert acoustic signal into analogue signals. For example, the acoustic emission sensors may comprise those described in <CIT>.

Each acoustic emission sensor <NUM>, <NUM> is optionally coupled to a respective bandwidth reduction module <NUM>, <NUM>, and an optional downsampling module <NUM>, <NUM>. In the example shown in <FIG> the bandwidth reduction modules <NUM>, <NUM> and the downsampling modules <NUM>, <NUM> are arranged in series, but it will be understood that in other examples the modules may be provided in parallel and/or the functionality provided by the same component. In addition, it will be understood that the optional downsampling modules <NUM>, <NUM> and/or the optional bandwidth reduction modules <NUM>, <NUM> may be provided as part of the acoustic emissions sensors <NUM>, <NUM> and/or as part of the filter module <NUM>.

In the example shown in <FIG>, each optional downsampling module <NUM>, <NUM> is coupled to a filter module <NUM>. In the example shown, the filter module comprises a first ANC input <NUM> for receiving signals from the first acoustic emission sensor <NUM> and a second ANC input <NUM> for receiving signals from the second acoustic emission sensor <NUM>.

The filter module <NUM> comprises active noise cancellation circuitry. For example, the filter module may comprise an ams® AS342x Ambient Noise Cancellation Speaker Driver. In some examples the filter module <NUM> comprises an internal OTP-ROM that can optionally be used to store gain calibration settings as well as all application specific settings.

In the example shown in <FIG>, the filter module <NUM> comprises a diagnostic module <NUM>, coupled to the filter module <NUM> such that it receives two outputs from the filter module corresponding to signals received from the first acoustic emission sensor <NUM> and the second acoustic emission sensor <NUM>. It will be understood that being provided as part of the filter module <NUM> may mean that the diagnostic module <NUM> is provided in a common enclosure or housing with the filter module <NUM>.

The diagnostic module <NUM> may comprise, among other features, a processor, a memory (e.g. a non-transitory medium configured to store instructions for execution by the processor, data, and/or other information), and/or an input/output (I/O). The I/O may include one or more I/O interfaces and may receive noise-cancelled signals from the first acoustic emission sensor <NUM> and the second acoustic emissions sensor <NUM> via the filter module <NUM>.

Although the diagnostic module <NUM> shown in <FIG> is shown as being (functionally, at least) part of the filter module <NUM>, it will be understood that in some examples (as in <FIG>), the diagnostic module <NUM> may be provided remote from the filter module <NUM>, such as in the cloud or on a remote device or controller, such as a controller for the system being monitored.

In addition, although the acoustic emission sensors <NUM>, <NUM> are shown as being separate to the filter module <NUM>, it will be understood that in some examples the acoustic emission sensors <NUM>, <NUM> (and also optionally the optional bandwidth reduction modules <NUM>, <NUM>, and optional downsampling modules <NUM>, <NUM>) may additionally or alternatively be provided as part of the filter module <NUM>, for example within a common housing or enclosure.

The acoustic emissions sensors <NUM>, <NUM>, which may be incorporated into the filter module <NUM>, are configured to output a signal (for example, to the diagnostic module <NUM> or other component) indicative of an operational condition of a seal interface of the dry gas seal (e.g., an operational condition of a first seal face relative to a second seal face).

The respective optional bandwidth reduction modules <NUM>, <NUM> may be configured to reduce the bandwidth of the signals output from the respective acoustic emissions sensors <NUM>, <NUM>. For example, the bandwidth reduction modules <NUM>, <NUM> may be configured to envelope the respective signals.

The respective optional downsampling modules <NUM>, <NUM> may be configured to downsample the respective signals from the acoustic emission sensors <NUM>, <NUM>. For example, the downsampling modules <NUM>, <NUM> may be configured to take a route mean square of the respective signals.

The filter module <NUM> may be configured to provide active noise cancellation based on a comparison of the signals received from the respective first and second acoustic emission sensors <NUM>, <NUM>, for example by providing feed-back cancellation with filter loop transfer function.

The optional diagnostic module <NUM> may be configured to use the respective noise-cancelled signals corresponding to the first acoustic emission sensor <NUM> and the second acoustic emissions sensor <NUM> from the filter module <NUM> to establish an operating condition of the seal and/or determine one or more other parameter values related to the seal based at least in part on the received signals. In some cases, based at least in part on the respective noise-cancelled signals (for example, the time domain and/or frequency domain of the signals), the diagnostic module <NUM> may be configured to determine parameter values relating to the seal including, but not limited to, a lift off at the seal interface, a touch down at the seal interface, when maintenance is needed, an operating condition of the seal interface, and/or other suitable parameter values related to operation of the seal.

In some examples, the diagnostic module <NUM> may be configured to detect and/or predict failure based on at least one of: loss of lubrication resulting in seizure; presence of foreign matters; pressure reversal of lubricating fluid; mechanical failure e.g. scars marked on respective portions of the bearing. This may be indicated, for example, by cavitation.

The analysis performed by the diagnostic module <NUM> may comprise determination of high order statistical values such as Skewness and Kurtosis to help identify potential faults. In some examples such a statistical analysis may be combined with use of a Fast Fourier Transform to provide an indication of the health of the system, for example as described in <CIT>. For example, the diagnostic module <NUM> may be configured to apply the following equation (Equation <NUM>) to determine the condition of the system being monitored: <MAT> Where:.

<MAT>  is the average FFT (Fast Fourier Transformation) for first Z frequency bands, whereby Z is an integer
FFTshaft  is the Fast Fourier Transformation for the first frequency of the coupling shaft
FFTshaft<NUM>  is the Fast Fourier Transformation for the second frequency of the coupling shaft is the Fast Fourier Transformation for the nth
FFTshaftN  frequency of the coupling shaft, whereby n is an integer and n < Z
C<NUM>  is the Skewness value
C<NUM>  is the Kurtosis value.

The above equation is a typical example of mathematical statistical function used to determine coupling health. Other combinations of values in mathematical statistical function may provide similar results and may be used without departing from the scope of the invention as defined by the claims.

In use, the acoustic emission sensors <NUM>, <NUM> may output a signal indicative of their measurements to the filter module <NUM> and/or optional diagnostic module <NUM> for processing (for example, for processing by a processor and/or other computing component). These signals are sent via the optional bandwidth reduction modules <NUM>, <NUM> and/or the optional downsampling modules <NUM>, <NUM> to respective inputs of the filter module <NUM>. The active noise cancelling circuitry in the filter module <NUM> performs active noise cancellations and outputs signals to the diagnostic module <NUM>.

For example, both time domain and frequency domain of the noise-cancelled signals are sent to the diagnostic module <NUM> to determine the occurrence and frequency of signal characteristics with respect to the system being monitored. For example, the diagnostic module <NUM> may use Equation <NUM> to determine the condition of the system being monitored.

In some examples the diagnostic module may be configured to further provide some form of feedback to the user. For example, the apparatus may comprise a plurality of visual indicators, such as LEDs, that provide an indication of the condition of the system to a user. For example, if the condition of the system is such that it is operating within a first selected range, a first visual indication (such as the illumination of green LEDs) may be provided to the user, indicating that the system is running correctly. If the condition of the system is such that it is operating within a second selected range, a second visual indication (such as the illumination of amber LEDs) may be provided to the user, which may indicate that the system is not running optimally and/or a predicted failure of a component such as the seal. If the condition of the system is such that it is operating within a third selected range, a third visual indication (such as the illumination of red LEDs) may be provided to the user, which may indicate that the system is not running correctly and may indicate a failure of a component of the system such as the seal.

In one example, as a seal face of a seal rotates with respect to at least one other seal face of the seal, the seal may emit a sound and the sound may change over time as the seal faces separate from one another (e.g., during run-up of the seal and/or the system to which the seal is applied) and/or come into contact with one another (e.g., during rundown of the seal and/or the system to which the seal is applied), and the acoustic emissions sensors <NUM>, <NUM> may be configured to sense the emitted sound and provide an indication of when a lift off (e.g., initial separation of the first seal face and the second seal face after the seal faces have been touching) occurs and/or when a touch down (e.g., initial contact between the first seal face and the second seal face as the relative rotation of the seal faces of the seal slows down) occurs.

Although the apparatus described in <FIG> uses first and second acoustic emission sensors <NUM>, <NUM>, it will be understood that the apparatus may make use of other and/or additional sensors, and that signals indicative of the outputs of these sensors may be provided to the filter module <NUM> and/or the diagnostic module <NUM>. For example, the system may additionally comprise a speed sensor (for example, providing an indication of the speed of revolution of the machinery), and the diagnostic module <NUM> may use signals from the speed sensor in determining the condition of the system.

<FIG> shows another example of a condition monitoring apparatus <NUM>. The apparatus <NUM> shown in <FIG> shares many features in common with the apparatus <NUM> shown in <FIG>, and it will be understood that features described above in relation to the apparatus shown in <FIG> may be used with the example apparatus <NUM> shown in <FIG>, and vice versa.

The apparatus <NUM> shown in <FIG> additionally comprises optional respective pre-amplifiers <NUM>, <NUM> coupled to respective acoustic emission sensors <NUM>, <NUM>.

Coupled to each pre-amplifier <NUM>, <NUM>, in parallel, are respective RMS modules <NUM>, <NUM>, and respective enveloper modules <NUM>, <NUM>. Each of these modules <NUM>, <NUM>, <NUM>, <NUM> are coupled to respective inputs <NUM>, <NUM> of the filter module <NUM>, such that the filter module comprises a pair of RMS inputs <NUM> coupled to the two RMS modules <NUM>, <NUM>, and a pair of envelope inputs <NUM> coupled to the two enveloper modules <NUM>, <NUM>.

In the example shown in <FIG> the filter module <NUM> also comprises an optional communications interface <NUM>, coupled wirelessly to a diagnostic module <NUM> which is provided remotely, such as in the cloud.

The RMS modules <NUM>, <NUM> are configured to obtain a first route mean square, RMS, signal from the first acoustic emission sensor <NUM>, and a second RMS signal from the second acoustic emission <NUM>.

The enveloper modules <NUM>, <NUM> are configured to obtain a first envelope signal from the first acoustic emission sensor <NUM>, and a second envelope signal from the second acoustic emission sensor <NUM>.

The filter module <NUM> shown in <FIG> is configured to perform active noise cancellation based on a comparison of the first RMS signal and the second RMS signal, and the first envelope signal and the second envelope signal.

In some examples the comparison comprises a mathematical operation between the first RMS signal and the second RMS signal, and a mathematical operation between the first envelope signal and the second envelope signal, such that the comparison is between each pair of signals received by each of the two pairs of inputs <NUM>, <NUM> of the filter module <NUM>.

The mathematical operation may comprise a subtraction between the first RMS signal and the second RMS signal, and a subtraction between the first envelope signal and the second envelope signal.

The communications interface <NUM> is configured to transmit (for example, wirelessly, such as via Wi-Fi® or Bluetooth®) signals to the diagnostic module <NUM>. It will be understood that the communications interface <NUM> may not be configured to send signals to the diagnostic module <NUM> directly but may send the signals via one or more intermediate nodes or routers and via a combination of different communications networks and/or protocols.

<FIG> shows another example of a condition monitoring apparatus <NUM>. The apparatus <NUM> shown in <FIG> shares many features in common with the apparatus <NUM> shown in <FIG>, and it will be understood that features described above in relation to the apparatus shown in <FIG> and in <FIG> may be used with the example apparatus <NUM> shown in <FIG>, and vice versa.

The main difference between the apparatus <NUM> shown in <FIG> and the apparatus <NUM> shown in <FIG> is that in the apparatus <NUM> shown in <FIG>, the filter module <NUM> and the diagnostic module <NUM> are both remote to the acoustic emission sensors <NUM>, <NUM> and the system being monitored. As such, the apparatus <NUM> comprises an optional communications interface <NUM> for sending signals received from the first acoustic emission sensor <NUM> and the second emission sensor <NUM> (and that have been reduced in bandwidth and/or downsampled) to the filter module <NUM> and the diagnostic module <NUM>.

<FIG> shows a schematic view of another example condition monitoring apparatus <NUM>, and is very similar to the apparatus <NUM> described above with reference to <FIG>. The apparatus <NUM> in <FIG> additional comprises the introduction of a phantom power supply to the respective outputs from the first acoustic emission sensor <NUM> and the second acoustic emission sensor <NUM>, as well as showing that the first and second acoustic emission sensors <NUM>, <NUM> and optional pre-amplifiers <NUM>, <NUM> are grounded.

<FIG> also shows how the outputs from the first and second acoustic emission sensors are at around <NUM>, whereas when they are received at the filter module <NUM> after having been through the respective RMS <NUM>, <NUM> and enveloper <NUM>, <NUM> modules, the signal is at around <NUM>.

<FIG> shows an example circuit <NUM> for enveloping used in the enveloper modules described above. The circuit <NUM> shown in <FIG> is configured to rectify the first acoustic emission signal prior to obtaining the first envelope signal, and rectify the second acoustic emission signal prior to obtaining the second envelope signal.

<FIG> shows example outputs of a condition monitoring system according to an example of the disclosure.

<FIG> shows an example method of monitoring the condition of a system comprising rotating or reciprocating machinery and a seal, for example using the apparatus of any of <FIG> described above.

The method comprises obtaining <NUM> first acoustic emission data emitted from the seal (for example, via the first acoustic emission sensors as described above), obtaining <NUM> second acoustic emission data emitted from the rotating or reciprocating machinery - such as a pump (for example, via the second acoustic emission sensors as described above), and performing <NUM> active noise cancellation based on a comparison of the first acoustic emission data and the second acoustic emission data (for example, via the filter module as described above).

The method may further comprise reducing the bandwidth of the first acoustic emission data and/or the second acoustic emission data prior to performing active noise cancellation, for example prior to performing <NUM> active noise cancellation.

The method may further comprise reducing the number of samples of the first acoustic emission data and the second acoustic emission data, for example prior to performing <NUM> active noise cancellation.

The method may further comprise, for example prior to performing <NUM> active noise cancellation, obtaining:.

and performing active noise cancellation based on a comparison of at least one of:.

It will be understood that the method may comprise performing active noise cancellation based on a comparison of both (i) the first RMS signal and the second RMS signal, and (ii) the first envelope signal and the second envelope signal. The comparison may comprise a mathematical operation between the first RMS signal and the second RMS signal, and a mathematical operation between the first envelope signal and the second envelope signal.

In some examples the method further comprises rectifying the first acoustic emission signal prior to obtaining the first envelope signal, and rectifying the second acoustic emission signal prior to obtaining the second envelope signal.

After performing <NUM> active noise cancellation, the method may further comprise outputting a noise-cancelled signal, and determining a condition of the system based on the noise-cancelled signal. For example, the condition of the system may be determined via the diagnostic module as described above.

It will be understood that, to enable this determination of the condition of the system, in some examples the method may comprise transmitting the noise-cancelled signal to a remote device via a communications interface for determining a condition of the system.

It will also be understood that a computer readable non-transitory storage medium comprising a program for a computer configured to cause a processor to perform the method as described above may be provided.

Claim 1:
A system comprising a condition monitoring apparatus (<NUM>. <NUM>, <NUM>, <NUM>) the system comprising rotating or reciprocating machinery and a seal, the condition monitoring apparatus comprising:
a first acoustic sensor (<NUM>, <NUM>, <NUM>, <NUM>) coupled proximate to the seal for providing a first acoustic emission signal;
a second acoustic sensor (<NUM>, <NUM>, <NUM>, <NUM>) coupled proximate to the rotating or reciprocating machinery for providing a second acoustic emission signal; and
a filter module (<NUM>, <NUM>, <NUM>, <NUM>), wherein the filter module (<NUM>, <NUM>, <NUM>, <NUM>) is configured to perform active noise cancellation based on a comparison of the first acoustic emission signal and the second acoustic emission signal.