Patent Application
20230349751
The present disclosure relates to device and method for distributed sensing.
The disclosure relates to distributed or fully distributed sensors, in which an optical fiber is a long uninterrupted sensor, and the measured information are extracted from the analysis of backscattered light.
Most of the assets measured or monitored using DFOS (Distributed Fibre Optic Sensing) are linear. This is the case for power cable, for oil and gas pipeline, likewise for water pipeline. In such linear system, the limit is the maximum measurement range.
There are some structures that are similar to star network configuration rather than linear configuration. These are for instance the inter-array cable (IAC) inside windfarm or the gathering lines for the pipeline industry or the fibre-based telecommunication network (point-to-multipoint fiber-to-the-home (FTTH) network, also defined as a PON network) or lines in water / gas/ distribution pipelines or in sewage.
Monitoring of such a star network is difficult.
One possibility is to use multiple channels that are measured one after the other, in sequence. This is only possible when the targeted events have a slow time constant with respect to the sequence. For example, measuring temperature with a Distributed Temperature Sensing (DTS) is compatible with a sequence/channel-based approach. Assuming 10 channels and 3 min to measure one channel, then every channel is measured twice per hour. Given that the time constant of an IAC on thermal variation is in the 3h to 5h range, there is still a good coverage of the temperature.
This is not the case when looking at short event like anchor drop and short circuit. A short circuit may last for a few 10s of milliseconds. In other words, when using a 5 min measurement and 30 min sequence, most of the short circuits will not be detected, as they will appear in the non-measured channel. In this case, a sequence/channel-based approach is not possible.
One could:
The disclosure presents a device and/or method for distributed sensing, e.g., arranged for a star network, that is less complex and/or less expensive than prior art but with similar or better performances.
An aspect of the disclosure concerns a device for distributed sensing comprising:
The pump signal is, in some implementations, a pulsed pump signal, and the controller is, in some implementations, configured (e.g., arranged and/or programmed) to control so that each gate is, in some implementations, one after the other, in its open state a longer time than the duration of the pulsed pump signal in order to allow the pulsed pump signal to fully pass or go through the gate in its open state.
The controller can be configured (e.g., arranged and/or programmed) in order to avoid injecting the pump signal in at least two channels at the same time.
The optical receiver can comprise, for each channel, a circulator, arranged for:
The backscattered signal can comprise a Rayleigh backscattered signal, a Brillouin backscattered signal, or a Raman backscattered signal.
Each channel can comprise an optical fiber monitoring a cable, pipe, branch or string of a star network, in some implementations, monitoring an inter array cable of a star network of a wind farm.
At least one of the channels can be arranged for monitoring several cables, pipes, branches and/or strings departing in several different directions from a central position of the star network, the optical fiber of this at least one channel going back and forth with respect to the central position.
Each channel can comprise an optical fiber monitoring at least one cable, pipe, branch and/or string of at least one among a pipeline network, a transport network such like a road or rail network, a telecommunication network, an information network, or an electrical network.
The optical receiver can comprise a detector shared for all the channels.
The controller can be configured (e.g., arranged and/or programmed) in order to allow at least two gates to be in the open state at the same time.
An aspect of the disclosure concerns a wind farm comprising a device according to the disclosure.
An aspect of the disclosure concerns a method for distributed sensing comprising:
The pump signal is in some implementations a pulsed pump signal, and each gate is in some implementations, in some implementations one after the other, in its open state a longer time than the duration of the pulsed pump signal in order to allow the pulsed pump signal to fully pass or go through the gate in its open state.
The splitting step can avoid injecting the pump signal in at least two channels at the same time.
The optical receiver can comprise, for each channel, a circulator:
The backscattered signal can comprise a Rayleigh backscattered signal, a Brillouin backscattered signal, or a Raman backscattered signal.
Each channel can comprise an optical fiber monitoring a cable, pipe, branch or string of a star network, in some implementations, monitoring an inter array cable of a star network of a wind farm.
At least one of the channels can be monitoring several cables, pipes, branches and/or strings departing in several different directions from a central position of the star network, the optical fiber of this at least one channel going back and forth with respect to the central position.
Each channel can comprise an optical fiber monitoring at least one cable, pipe, branch and/or string of at least one among a pipeline network, a transport network such like a road or rail network, a telecommunication network, an information network, or an electrical network.
The optical receiver can comprise a detector shared for all the channels.
The splitting step can allow at least two gates to be in the open state at the same time.
The method according to the disclosure can be used for monitoring a wind farm.
Other advantages and characteristics of the disclosure will appear upon examination of the detailed description of embodiments which are in no way limitative, and of the appended drawings in which:
These embodiments described herein being in no way limitative, we can consider variants of the disclosure including only a selection of characteristics subsequently described or illustrated, isolated from other described or illustrated characteristics (even if this selection is taken from a sentence containing these other characteristics), if this selection of characteristics is sufficient to give a technical advantage or to distinguish the disclosure over the state of the art. This selection includes at least one characteristic, in some implementations, a functional characteristic without structural details, or with only a part of the structural details.
The disclosure relates to distributed or fully distributed sensors, in which an optical fiber is a long uninterrupted sensor, and the measured information are extracted from the analysis of backscattered light.
The backscattered light can typically come from the following scatterings:
We are now going to describe, in references to
Device 101 for distributed sensing comprises a pump generator 1 arranged for generating a pulsed optical pump signal 5.
“Pulsed” optical signal 5 means a pulse regardless of its duration, for example short duration (of the order of a picosecond or femtosecond) or long duration (of the order of a few minutes or longer) or intermediate duration.
Pulse 5 duration is typically from one picosecond to 10 microseconds.
Pump generator 1 comprises typically a laser or a light-emitting diode, arranged for generating or emitting signal 5:
However other kind of pump generator 1 may be employed within the scope of this disclosure.
Device 101 comprises the optical pump splitter 2 configured to receive the pump signal 5 and split the pump signal 5 in a number N of channels 3 (N being an integer greater than or equal to 2), each channel 3 comprising an optical fiber 31 and/or a connector 32 arranged for connecting an optical fiber 31.
Each connector 32 can also be called “pump connector” 32 as it is arranged and used to connect one of the fibers 31 to the pump generator 1.
Each fiber 31 is typically:
Connector 32 comprise a standard connector for optical fiber 31 or other suitable connection means.
The optical pump splitter 2 comprises:
Each gate 21 can also be called “pump gate” 21 as it is arranged and used to control if the pump signal 5 enters into one of the fibers 31 or not.
Each gate 21 could be home designed using:
The pump signal is a pulsed signal, and each gate 21 is (e.g., one after the other) in its open state a longer time than the duration of the pulsed pump signal 5 in order to allow the pulsed pump signal to fully pass or go through the only one gate in its open state while the pump signal 5 reaches the gates 21.
Device 101 comprises a controller (not illustrated) configured to control the optical pump splitter 2. The controller can include at least one computer, one central processing or computing unit, one analogue electronic circuit (e.g., dedicated), one digital electronic circuit (e.g., dedicated) and/or one microprocessor (e.g., dedicated) and/or software means or other control means known in the art for controlling the optical pump splitter 2.
Device 101 comprises an optical receiver 4 arranged for receiving a backscattered signal 6 from the optical fiber 31 or from the connector 32 of each channel 3, this backscattered signal 6 being generated in fiber 31 in response to the pump signal 5.
As illustrated in
More precisely, each channel 3 comprises an optical fiber 31 monitoring at least one cable of a pipeline network, a transport network such like a road or rail network, a telecommunication network, an information network, or an electrical network.
The proposed solution of device 101 is thus a time-division multiplexing of the pump signal 5. In this way, each branch (cable or pipe) 7 can be covered by a single fiber 31 providing also a better signal quality.
At least one channel 3 is arranged for monitoring several branches 7 departing in several different directions from a central position of the star network; this at least one channel 3 going back and forth several times with respect to the central position. For example:
Thus, for short event measurement and/or simultaneous measurement, it is possible to design the sensing path of fiber 31 by following one branch (cable or pipe) 7 to the end (following what is known as a string in the windfarm jargon) and come back to the device 101 (i.e. to the central position of the star network, known as the offshore substation in the windfarm jargon) before going to the next branch 7, as illustrated in
In case of fiber 31c, the return path is useless. Assuming that each branch 7 is 10 km long and the range of the Distributed Acoustic Sensing (DAS) device 101 is 50 km, then it is possible to measure three strings 7 only per fiber 31, with two return paths, each of 10 km (10 km sensing - 10 km return - 10 km sensing - 10 km return - 10 km sensing). In this specific example of fiber 31c, 40% of the fiber length is not employed for active measurement (the return paths).
As illustrated by fiber 31a in
As illustrated in
Pump generator 1 is arranged for generating pulse 5 several times, in some implementations at a temporal period Tp.
The controller is arranged in such a way that, each time pulse 5 is generated, this pulse 5 is split by the optical pump splitter 2 and reach each gate 21 of each channel 3, but only one of this gate 21 is in its open state 211, the other ones are in the closed state 210.
The controller is arranged in such a way that the gates 21 are in their open state 211 one after the other, and in such a way that, for a temporal period TN comprising N generated pulses 5 for N gates of N channels 3, pulse number I (i is an integer equal to 1 to N), reaches all the gates 21 but only gate 21 number i of channel 3 number i is in its open state. This way, during a temporal period TN (TN = N × TP), every fiber 31 of every channel 3 receives one by one pulse 5, one after the other.
Also, as illustrated by
This perfectly illustrates technical advantages of device 101 according to the disclosure, compared to prior art (especially compared to a prior art solution using a very fast optical switch):
The fiber 31 reached by signal 5 is generating a backscaterred signal 6.
The backscattered signal 6 comprises a Rayleigh backscattered signal, a Brillouin backscattered signal, or a Raman backscattered signal. In case of
The optical receiver 4 typically comprises, for each channel 3, a circulator 41.
For each channel 3, the circulator 41 of this channel 3 is arranged for:
The optical receiver 4 typically also comprises:
It is also possible to have a single EDFA (not illustrated) at the exit of the 3×1 coupler 43 (rather than having three EDFA on each input of the 3×1 coupler 43). Having the 3×1 coupler first is possible for short string only. The EDFA after is thus limited to a small channel number (reasonably up to 4) and short range.
The data or signal 6 acquired by optical receiver 4 or detector 44 is then analyzed according to the classical design of the interrogator, the controller being configured (e.g., arranged and/or programmed) to know, depending on time, from which channel 3 is coming signal 6, based on the channel 3 that most recently received the pulse 5.
The analysis is backscattering dependent, typically:
Thus, in device 101, the pump signal 5 is split in N (assuming N channels 3, practically N equal three or four). But as such, the N channels 3 are synchronized (they receive the pump 5 simultaneously) and measurement by optical receiver 4 is done from each channel 3.
To maintain a “in series” measurement, the pump 5 is triggered at the max speed corresponding to the length L of the channel 3 (assuming for simplicity that the N channels 3 have an identical length L), which is N times faster than what is allowed for all the channels and a gating system let one pump 5 out of N go through to the relevant channel 3.
Detection is done easily as all channels 3 receive the pump 5 in series and a single acquisition can be done.
Let’s assume three channels 3 of 25 km each, for a total length of 75 km. The pulse rate would be 1.33 kHz max. Here, the pulse 5 is repeated at three times the pulse rate (4 kHz), with pulses i going to the first channel, pulse i+1 going to the second channel 3 and pulse i+2 going to the third channel 3 in cycles, so that each channel 3 receives pulses at 1.33 kHz in the proper timing. Performances are those of 25 km in term of signal quality, since each pump 5 travels 25 km only instead of 75 km, with the frequency bandwidth equivalent to 75 km (1.33 kHz/2 to take into account sampling theory) because of the total measuring time.
Device 101 is directly compatible with any single-based measurement system (like Raman Distributed Temperature Sensing (DTS) for instance) and is not limited to a particular type of Distributed Acoustic Sensing (DAS) interrogator. In fact, it is applicable to all fiber sensing devices working with a single fiber.
Device 101 is directly compatible with a Brillouin Optical Time Domain Reflectometry (BOTDR) (temperature or strain).
It is also noted the following various advantages of device 101:
We are now going to describe, in references to
Device 102 will be described only for its differences compared to device 101.
In case of
As illustrated by
The pump gating does not have to be symmetric and could be adapted to match the actual length of each string, provided that it is possible to generate pump signals 5 with different time interval.
Compared to device 101, device 102 further comprises a probe generator 111 for generating the optical probe signal 8.
Probe generator 111 comprises typically a laser or a light-emitting diode.
However other kind of probe generator 111 may be employed within the scope of this disclosure.
The probe signal 8 typically:
Compared to device 101, device 102 further comprises an amplifier 9, in some implementations, an Erbium-Doped Fiber Amplifier (EDFA), arranged for amplifying the probe signal 8 before being the optical probe splitter 10, 11 described below.
Each channel 3 comprises an optical fiber 31 and/or:
Connector 322 comprise a standard connector for optical fiber 31 according to prior art or other suitable connection means.
Compared to device 101, device 102 further comprises the optical probe splitter 10, 11 arranged for splitting the probe signal 8 in the N channels 3.
The optical probe splitter 10, 11 for splitting the probe signal 8 comprise:
Each probe gate 11 could be home designed using:
The controller (not illustrated) is configured (e.g., arranged and/or programmed) to keep the gate 11 of a given channel 3 in its open state 218 during all time signal 6 is acquired from this same channel 3 by optical receiver 4 and/or detector 44, while all the other gates 11 are in the closed state.
The gates 11 can be in the open state 218 only one by one.
The gates 21 and the gates 11 are respectively at two opposite ends of the fibers 31.
An embodiment of wind farm according to the disclosure comprises device 101 or 102.
We are now going to describe, in reference to
This method for distributed sensing comprises:
The optical fiber 31 of each channel 3 is monitoring:
At least one channel 3 is monitoring several cables departing in several different directions from the central position of the star network, the optical fiber 31 of this at least one channel 3 going back and forth with respect to the central position.
Device 101 and/or 102 is, in some implementations, used for monitoring a wind farm.
Of course, the disclosure is not limited to the examples which have just been described and numerous amendments can be made to these examples without exceeding the scope of the disclosure.
For example, at least one fiber 31 or each fiber 31 can comprise a Fibre Bragg Grating (FBG). In this case, signal 5 is not necessary a pulsed signal 5 but can be a pulsed signal 5 or a continuous signal 5. Nevertheless, this embodiment is not a preferred embodiment, because if signal 5 is a continuous signal 5, then the gating is more complex, because the controller is then configured (e.g., arranged and/or programmed) in order to avoid at least two gates 21 to be in the open state 211 at the same time.
Of course, the different characteristics, forms, variants and embodiments of the disclosure can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. In particular, all variants and embodiments described above can be combined with each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22171178.1 | May 2022 | EP | regional |
