Environmental monitoring system

Abstract

An environmental monitoring system (100) suitable for monitoring at least one environmental parameter, wherein the environmental monitoring system (100) comprises at least one remote sensor unit (200) configured to measure an environmental parameter and a common control unit (300), wherein the at least one remote sensor unit (200) and common control unit (300) are connected by a communication interface in the form of an optical fibre cable (400).

Description

[0001] Environmental monitoring system

[0002] The disclosed embodiments relate to an environmental monitoring system.

[0003] The disclosed embodiments especially relate to an environmental monitoring system utilizing remote sensor units arranged to an optical fibre cable.

[0004] Background

[0005] There is an increasing focus on the environment and especially the need for monitoring the environment to detect changes both as regards short-time changes and long-time climate changes.

[0006] One of the areas where monitoring of the environment has gained interest the last years is the ocean temperature that have large effects. Being able to measure ocean temperatures over long time (10-30 years) with accuracy has proven to be a problem, mainly due to the ocean is a harsh environment for sensors, but also due to the fact that large areas are inaccessible due, e.g., ice or depth. Another problem one has been facing is that sensor over time drift and the accuracy of the measurement deteriorates. All sensors are affected by noise and drift to some degree. Drift is mainly due to aging, which means that the component deviates slightly from its calibrated values and gives results that reflect its own variations rather than the reality it measures.

[0007] Over the years there have been made attempts to minimize this drift as much as possible. One common way is to avoid analogue steps in the sensor, as analogue components and converters tend to create both noise and drift.

[0008] A solution is to use oscillators as sensors, and then measure the frequency instead of the analogue value. Measuring a frequency can be done digitally (l's and 0's) and this eliminates the uncertainty of measuring an analogue value (0 to 1).

[0009] Example of such oscillators are quartz crystal sensors, that among others, enable the possibility to measure ocean temperature, as, e.g., described in US2015023388 AA, JP2012032194 A2, JP63311133 A2, JP63284439 A2 and JP59032834 A2.

[0010] A common disadvantage with the prior art solutions is that, even if they provide sensors having lower drift perse, they still require local components to handle the processing of the measurements, such as frequency counter, reference clock and microcontroller. Due to requiring the mentioned local components, each sensor will be costly to produce and install, as well as they will require maintenance.

[0011] As there have to be at least two crystals in such an application (one for measuring and one for reference), the error will statistically be twice of one crystal. Also, maintenance and calibration will require retrieval of the sensors, a task being difficult to perform and, in some applications, also impossible.

[0012] There is accordingly a need for an environmental monitoring system solving the drawbacks and lacks of the prior art solutions.

[0013] Summary

[0014] The disclosed embodiments provide an environmental monitoring system partly or entirely solving the drawbacks and lacks of prior art solutions.

[0015] Provided herein is an environmental monitoring system with a minimum or no use of analogue parts that could significantly influence the measurement.

[0016] Also provided herein is an environmental monitoring system with low or no maintenance.

[0017] Provided herein is an environmental monitoring system enabling the use of low drift sensors.

[0018] Also provided herein is an environmental monitoring system requiring the minimum of electronic components at a measuring point.

[0019] Provided herein is an environmental monitoring system enabling the use of with low aging sensors.

[0020] Also provided herein is an environmental monitoring system enabling different measuring methods to be used and changed.

[0021] Provided herein is an environmental monitoring system enabling the use of low power consumption sensors.

[0022] Also provide herein is an environmental monitoring system enabling the use a high number of sensors due to low sensor costs. Provided herein is an environmental monitoring system supporting long remote distances due to having no latency issues.

[0023] Also provided herein is an environmental monitoring system having a large number of application areas.

[0024] Provided herein is an environmental monitoring system that can be retrofitted to existing optical fibre cables or arranged to new optical fibre cables.

[0025] Provided herein is an environmental monitoring system that configured to make use of (standard) optical fibre cables configured to transfer data.

[0026] Also provided herein is an environmental monitoring system enabling the arrangement of multiple sensors along the optical fibre cable.

[0027] Also provided herein is an environmental monitoring system that can be used for monitoring environmental parameters both in the air, in the ground and in water (submerged).

[0028] Further features of the present invention will appear by consideration of the following description, claims and attached drawings.

[0029] The invention

[0030] An environmental monitoring system according to the present invention is defined by the technical features of claim 1. Preferable features of the environmental monitoring system are described in the dependent claims.

[0031] The disclosed embodiments of the present invention provide an environmental monitoring system (EMS) suitable for monitoring at least one environmental parameter.

[0032] The EMS according to the present invention comprises at least one remote sensor unit configured to measure an environmental parameter and a common (centralized) control unit, wherein the at least one remote sensor unit and common control unit are connected by a communication interface in the form of an optical fibre cable. According to one embodiment of the present invention, the optical fibre cable is configured to transfer data. In accordance with one embodiment of the present invention, the optical fibre cable is a standard optical fibre cable.

[0033] In accordance with the EMS according to the present invention, the remote sensor unit comprises at least one frequency-based sensor and an optical fibre connector connecting the at least one frequency-based sensor to the optical fibre cable. According to the present invention, the at least one frequency-based sensor is configured to provide a measurement signal of an environmental parameter. In accordance with the present invention, the optical fibre connector comprises an optical transmitter configured to generate light pulses based on the measurement signal of the at least one frequency-based sensor and transmitting by launching the generated light pulse into a dedicated or multiplexed optical fibre of the optical fibre cable with a desired wavelength. Accordingly, the optical transmitter transmits the measured value by the at least one frequencybased sensor into the optical fibre cable. By this is achieved a solution where the frequency-based sensor is configured to transmit directly on the optical fibre cable and wherein the sensor data are physically connected directly to the optical fibre cable without any intermediate or analogue means.

[0034] According to one embodiment of the EMS according to the present invention, the remote sensor unit comprises an integrated power supply enabling the remote sensor unit to operate without require power from external or additional sources.

[0035] In accordance with one embodiment of the optical transmitter according to the present invention, the optical transmitter is configured, by comprising means and / or software, to launch the light pulses into a dedicated or multiplexed optical fibre of the optical fibre cable as a direct light pulse or an on / off ethernet command. The use of an on / off ethernet command to launch light pulses will enable the optical fibre of the optical fibre cable to also be used for standard data packets, thus avoiding the requirement of a dedicated optical fibre.

[0036] In accordance with one embodiment of the remote sensor unit according to the present invention, the at least one frequency-based sensor is a temperature sensor, pressure sensor, pH-sensor, salinity sensor, gas sensor, CO2sensor, O2sensor or accelerometer, or a combination of two or more of these sensors, enabling the measurement of a desired environmental parameter.

[0037] According to one embodiment of the frequency-based sensor according to the present invention, the at least one frequency-based sensor is a quartz crystal sensor, especially suitable for measuring temperature. In accordance with a further embodiment of the EMS according to the present invention, the EMS comprises multiple remote sensor units distributed along the length of optical fibre cable. In this manner enabling measurements over long distances.

[0038] According to a further embodiment of the EMS according to the present invention, the remote sensor unit comprises a sensor control device configured to activate and deactivate the optical transmitter based on a transmit scheme or a query. By this is achieved that no communication protocols are required.

[0039] In accordance with the EMS according to the present invention, the common control unit comprises an optical fibre connector connecting the common control unit to the optical fibre cable. In accordance with one embodiment of the common control unit according to the present invention, the optical fibre connector comprises a beam splitter to connect the common control unit to a dedicated or multiplexed optical fibre of the optical fibre cable, and enabling receiving of the transmitted signal from the respective remote sensor unit.

[0040] According to an alternative embodiment of the EMS according to the present invention, wherein using a multiplexed optical fibre, the optical fibre connector is configured, by comprising means and / or software, to split out the data stream as on / off messages. As the bandwidth of the communication is considerably higher than the sensor frequency, this will not introduce considerable jitter.

[0041] According to one embodiment of the common control unit according to the present invention, the common control unit comprises a frequency counter connected to the beam splitter and configured to count received light pulses on the dedicated or multiplexed optical fibre of the optical fibre cable.

[0042] In accordance with one embodiment of the common control unit according to the present invention, the common control unit comprises a control device connected to the frequency counter and the optical fibre connector.

[0043] According to the EMC according to the present invention, the common control unit comprises an atomic reference clock or global navigation satellite system reference clock connected to the control device for measurement of the frequency of the frequency counter.

[0044] By the EMS according to the present invention is thus provided a system for measuring environmental parameters using remote sensor units that are connected to the same common control unit with a frequency counter and stable local reference clock. The EMS according to the present invention can be retrofitted to existing optical fibre cables or arranged to optical fibre cables to be deployed to enable them to be used for sensing of climate changes by enabling measurement of environmental parameters.

[0045] The EMS according to the present invention can be used for monitoring environmental parameters both in the air, in the ground and in water (submerged) and thus has a wide area of applications.

[0046] The remote sensor units according to the present invention have few electronic parts and minimum or no analogue parts that could significantly influence the measurement.

[0047] The EMS according to the present invention is based on remote sensor units that do not require maintenance or service, have low aging and further have a low power consumption.

[0048] Further, the EMS according to the present invention makes use of a common control unit where measuring methods can be changed, as well as provides easy calibration.

[0049] An advantage by the EMS according to the present invention is that the EMS supports repeaters in the optical fibre cable, as it is based on frequency and not time, and thus provides long remote distances as latency is no issue.

[0050] By the EMS according to the present invention it is provided a remote sensor unit having low costs resulting in that a high number of these can be arranged to the optical fibre cable at a fair cost.

[0051] Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

[0052] Example

[0053] The present invention will below be described in further detail with references to the attached drawings, where:

[0054] Fig. 1 is a principle drawing of a non-limiting embodiment of an environmental monitoring system according to the present invention, and

[0055] Fig. 2 is a principle drawing of a further non-limiting embodiment of the environmental monitoring system according to the present invention. Reference is now made to Fig. 1 showing a principle drawing of an environmental monitoring system (EMS) 100 according to a first embodiment of the present invention. The EMS 100 according to the present invention comprises at least one remote sensor unit 200 configured to measure an environmental parameter and a common control unit 300. According to the present invention, the at least one remote sensor unit 200 and common control unit 300 are connected by a communication interface in the form of an optical fibre cable 400.

[0056] In accordance with the present invention, the remote sensor unit 200 comprises at least one frequency-based sensor 210 being a sensor with an oscillating element sensitive to / capable of measuring an environmental parameter and provide a measurement signal of the environmental parameter.

[0057] According to the present invention, the at least one frequency-based sensor 210 is a temperature sensor, pressure sensor, pH-sensor, salinity sensor, gas sensor, CO2sensor, O2sensor, acoustic sensor, Acoustic Doppler Current Profiler (ADCP), or accelerometer. Other sensor will be within the knowledge of a skilled person.

[0058] In accordance with one embodiment of the remote sensor unit 200, the at least one frequencybased sensor 210 is a quartz crystal sensor capable of measuring temperature by vibrating at different frequencies depending on the temperature.

[0059] According to the present invention, the remote sensor unit 200 further comprises an optical fibre connector 211 connecting the at least one frequency-based sensor 210 to the optical fibre cable 400. In accordance with one embodiment of the remote sensor unit 200 according to the present invention, the optical fibre connector 211 comprises an optical transmitter 212 configured to generate light pulses based on the measurement signal of the at least one frequency-based sensor 210 and transmitting by launching the generated light pulses into a dedicated or multiplexed optical fibre 410 of the optical fibre cable 400 with a chosen wavelength. The chosen wavelength is according to the present invention preferably in the low frequency range 30-300 kHz, which is considerably different from the frequency range of 1 THz to 1000 THz used for optical communication in the optical fibre cable 400. In this manner the optical fibre cable 400 may be used both for communication and as a communication interface in the present invention.

[0060] In accordance with one embodiment of the optical transmitter 212 according to the present invention, the optical transmitter 212 is configured, by comprising means and / or software, to launch the light pulses into the dedicated or multiplexed optical fibre 410 of the optical fibre cable 400 as a direct light pulse or as an on / off ethernet command. The use of an on / off command will remove the requirement of a dedicated optical fibre and enable the optical fibre to also be used for transmitting standard data packages.

[0061] In accordance with one embodiment of the EMS 100 according to the present invention, the EMS 100 comprises multiple remote sensor units 200 distributed along the optical fibre cable 400 configured to measure the same or different environmental parameters by comprising at least one frequency-based sensor 210 tailored to measure a desired environmental parameter.

[0062] In accordance with one embodiment of the remote sensor unit 200 it further comprises a sensor control device 220, such as a microcontroller, configured to activate and deactivate the optical transmitter 211 based on a transmit scheme or a query. In accordance with a further embodiment of the remote sensor unit 200, the sensor control device 220 is configured to control the wavelength the optical transmitter 211 is transmitting with. In accordance with a further embodiment, the sensor control device 211 is configured to add an identifier, such as a header address, to the transmitted signal from the optical transmitter 211. In this manner the remote sensor unit 200 transmitting can be identified by the wavelength and / or identifier, or responding to a specific query issued by the common control unit 300, further described below.

[0063] In accordance with one embodiment of the EMS 100 according to the present invention, the common control unit 300 comprises an optical fibre connector 310 connecting the common control unit 300 to the optical fibre cable 400. In accordance with one embodiment of the common control unit 300, the optical fibre connector 310 comprises a beam splitter 311 connecting the common control unit 300 to the dedicated or multiplexed optical fibre 410 of the optical fibre cable 400 that the at least one remote sensor unit 200 is connected to and transmitting on.

[0064] According to one embodiment of the common control unit 300 it comprises a frequency counter 320 connected to the beam splitter 311. The frequency counter 320 is configured to count received light pulses on the dedicated or multiplexed optical fibre 410 of the optical fibre cable 400 transmitted by the at least one remote sensor unit 200.

[0065] The common control unit 300 according to the present invention further comprises a control device 330 connected to the frequency counter 320 and the optical fibre connector 310.

[0066] In accordance with the present invention, the common control unit 300 further comprises an atomic reference clock 340 or global navigation satellite system reference clock connected to the control device 330 for measurement of the frequency of the frequency counter 320. The control device 330 is further configured to, by comprising means and / or software, based on the measurements of the frequency counter 320 and clock 340, calculate a value of the measured environmental parameter. In accordance with a further embodiment of the control device 330, it is further configured to perform calibration of the measured environmental parameter.

[0067] In accordance with one embodiment of the common control unit 300, the control device 330 is configured to, by comprising means and / or software, identify the transmitting remote sensor unit 200 based on the wavelength frequency of the received signal and / or identifier.

[0068] In accordance with a further embodiment of the control unit 330, it comprises an optical transmitter 312 configured to transmit a query signal to the respective remote sensor unit 200 requesting the respective remote sensor unit 200 to transmit the measured value by the at least one frequencybased sensor 210.

[0069] Accordingly, by the present invention is provided an EMS 100 with remote sensor units 200 with minimum components, and wherein all remote sensor units 200 are connected to the common control unit 300 with a common frequency counter 320 and control device 330, enabling centralized calibration and choice of measuring method.

[0070] The EMS 100 according to the present invention can be retrofitted to an existing optical fibre cable 400 or arranged to a new optical fibre cable 400 to be deployed.

[0071] The EMS 100 according to the present invention has a wide area of application and will be suitable for monitoring environmental parameters both in the air, in the ground and in water (submerged).

[0072] Another example will be measuring, e.g., temperature, O2, CO2or similar in a mine. A further example could be to use an accelerometer to monitor movements in the ground, such as at the seabed, to be able to detect movements in the ground to give an early warning of earthquakes and tsunamis, or buried in the ground for detecting landslides or similar. A further example is to monitor pH, temperature, O2, CO2or similar in a lake or river.

[0073] As these few examples of different applications show, the EMS 100 according to the present invention can be implemented by retrofitting the remote sensor units 200 and common control unit 300 to an existing optical fibre cable 400 or connecting the remote sensor units 200 to an optical fibre cable 400 prior to deployment, such as into the ocean or into the ground.

[0074] A non-limiting example of use of the EMS 100 according to the present invention is for measurement of ocean temperatures over a long time (10-30 years) with high accuracy (in the range of millikelvins) that has been proven to be a difficult task with prior art solutions. With the EMS 100 according to the present invention however, where the remote sensor units 200 have very little drift and does not need service or maintenance after deployment, the task would be solvable.

[0075] By arranging remote sensor units 200 according to the present invention to a fibre cable 400 extending in air, in the ground or in water (submerged), the optical fibre cable 400 can be used by the EMS 100 according to the present invention to monitor climatic changes over time, such as temperature.

[0076] The remote sensor units 200 for this may include a frequency-based sensor 210 in the form of a quartz crystal sensor. By using, e.g., a frequency-based sensor 210 with a 172.0 kHz crystal having a custom 20 ppm, it will have a noise level of 3.44 Hz, or 0.002 %. Although the frequency-temperature characteristic of a such a sensor is nearly linear, it is not exactly so. A better model of this is using a second-order polynomial in temperature.

[0077] To calculate the frequency deviation for, e.g., the 262.144 kHz crystal at an actual temperature of A1°C, one can use the second-order polynomial equation: f = f x (a x (T - TO) + p x (T - T0)2)

[0078] Where (from actual samples): f = 262,144 Hz (nominal frequency) a = 34.5 ppm / °C (linear coefficient)

[0079] P = 0.018 ppm / °C2(quadratic coefficient)

[0080] AT = 1°C (actual temperature- reference temperature).

[0081] By using these values in the equation above, the result is:

[0082] Af = 262,144 x (34.5 x IO’6x (1) + 0.018 x IO’6x (l)2).

[0083] Solving the equation results in:

[0084] Linear term: 34.5 x 1 = 34.5 ppm

[0085] Quadratic term: (l)2= 1 0.018 x 1 = 0.018 ppm.

[0086] This results in total ppm deviation: 34.5 + 0.018 = 34.518 ppm.

[0087] The frequency dedication can thus be calculated as follows: Af = 262,144 x (34.518 / 106) -> Af = 9.05 Hz. In a non-limiting example of calculating counts over a 10 seconds sampling period this results in the following:

[0088] Af * 10 sec = 90.5 samples.

[0089] Temperature accuracy over a 10 seconds sampling period is then 1 / 90.5 = 0.011°C theoretically.

[0090] In another non-limiting example of calculating counts over a 60 seconds sampling period this results in the following:

[0091] Af * 60 sec = 543 samples.

[0092] Temperature accuracy over a 60 seconds sampling period is then 1 / 543 = 0.0018°C theoretically.

[0093] Accordingly, at an actual temperature A1°C and a reference temperature of 1°C, the frequency deviation of the 262.144 kHz crystal with a = 34.5 ppm and = 0.018 ppm is approximately 9.05 Hz. This means that the frequency will increase slightly by around 9.05 Hz from its nominal value at this temperature. By reading the temperature over a 10 seconds sampling period, one will get approx. 0.011°C theoretical accuracy etc. The longer sampling period, the more accurate measurement the EMS 100 according to the present invention provides.

[0094] Further, by sampling the sensor measurements with white noise, this would result in an improvement of 2 every time the number of samples are doubled and averaging the result.

[0095] By using a common control unit 300 for all remote sensor units 200, the method for calculating the temperature can be changed and used for all the remote sensor unit 200 measurements. All the measurements are further calibrated by using the same frequency counter 320 and reference clock 330.

[0096] Optical fibre cables 400 is known to have repeaters evenly distributed along the optical fibre cable 400 when the distance of the optical fibre cable 400 is over a certain distance. In the prior art solutions such repeaters will introduce latency in reported measurements, but due to the frequency counter 320, reference clock 340 and measurement method being centralized in the control device 330 in the common control unit 300, one will have full control over these. Accordingly, the only possible drift and noise will the come from the frequency-based sensor 210 itself, which can be monitored.

[0097] According to a further embodiment of the present invention, the remote sensor unit 200 comprises an integrated power supply 230 powering the components of the components 210-220 thereof. The integrated power supply 230 typically comprises at least one energy storage, such as one or more batteries or rechargeable supercapacitor. Other alternatives for energy storage will be within the knowledge of a skilled person. The sensor unit 200 may further be provided with energy harvesting means (not shown) for charging of the energy storage / power supply. Examples of such energy harvesting means are, but not limited to, such as saltwater batteries, resonant mechanical devices, piezoelectric devices, devices capable of transforming mechanical energy or kinetic energy, etc. Other alternatives for energy harvesting means will be within the knowledge of a skilled person. A skilled person will be familiar with these alternatives and no further description is required herein.

[0098] In accordance with one embodiment of the sensor unit 200 according to the present invention, the energy storage is charged by means of Power-over-fibre.

[0099] In accordance with the present invention, the common control unit 300 is provided with a communication interface (not shown) enabling communication with external units (not shown) for further processing of the measured data and presentation of data for a user.

[0100] The technical features of the above described embodiments may be combined to form modified embodiments within the scope of the attached claims.

Claims

Claims1. An environmental monitoring system (100) suitable for monitoring at least one environmental parameter, wherein the environmental monitoring system (100) comprises at least one remote sensor unit (200) configured to measure an environmental parameter and a common control unit (300), wherein the at least one remote sensor unit (200) and common control unit (300) are connected by a communication interface in the form of an optical fibre cable (400), wherein- the remote sensor unit (200) comprises at least one frequency-based sensor (210) configured to provide a measurement signal of an environmental parameter and an optical fibre connector (211) connecting the at least one frequency-based sensor (210) to the optical fibre cable (400), and- the optical fibre connector (211) comprising an optical transmitter (212) configured to generate light pulses based on the measurement signal of the at least one frequency-based sensor (210) and transmitting by launching the generated light pulses into a dedicated or multiplexed optical fibre (410) of the optical fibre cable (400) with a desired wavelength.

2. The environmental monitoring system (100) according to claim 1, wherein the remote sensor unit (200) comprises an integrated power supply (230).

3. The environmental monitoring system (100) according to claim 1, wherein the optical transmitter (212) is configured, by comprising means and / or software, to launch the light pulses into a dedicated or multiplexed optical fibre (410) of the optical fibre cable (400) as a direct light pulse or an on / off ethernet command.

4. The environmental monitoring system (100) according to claim 1, wherein the at least one frequency-based sensor (210) is a temperature sensor, pressure sensor, pH-sensor, salinity sensor, gas sensor, CO2sensor, O2sensor or accelerometer.

5. The environmental monitoring system (100) according to claim 1, wherein the at least one frequency-based sensor (210) is a quartz crystal sensor.

6. The environmental monitoring system (100) according to any preceding claim, wherein comprising multiple remote sensor units (200) distributed along the length of the optical fibre cable (400).

7. The environmental monitoring system (100) according to claim 1, wherein the remote sensor unit (200) comprising a sensor control device (220) configured to activate and deactivate the optical transmitter (211) based on a transmit scheme or a query.

8. The environmental monitoring system (100) according to claim 1, wherein the common control unit (300) comprises an optical fibre connector (310) connecting the common control unit (300) to the optical fibre cable (400), the optical fibre connector (310) comprising a beam splitter (311) to connect the common control unit (300) to a dedicated or multiplexed optical fibre (410) of the optical fibre cable (400).

9. The environmental monitoring system (100) according to claim 8, wherein the common control unit (300) comprising a frequency counter (320) connected to the beam splitter (311) and configured to count received light pulses or on / off messages on the dedicated or multiplexed optical fibre (410), respectively, of the optical fibre cable (400).

10. The environmental monitoring system (100) according to claim 1, wherein the common control unit (300) comprising a control device (330) connected to the frequency counter (320) and the optical fibre connector (310).

11. The environmental monitoring system (100) according to claim 10, wherein the common control unit (300) comprising an atomic reference clock (340) or global navigation satellite system reference clock connected to the control device (330) for measurement of the frequency of the frequency counter (320).

12. The environmental monitoring system (100) according to claim 10, wherein the control device (330) is configured, by comprising means and / or software, to calibrate the measured environmental parameter.

13. The environmental monitoring system (100) according to claim 1, wherein the optical fibre cable (400) is a standard optical fibre cable configured to transfer data.

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