DA COSTA ANTUNES PAULO FERNANDO (PT)
FERNANDES TEIXEIRA MESQUITA ESEQUIEL (PT)
DE BRITO ANDRÉ PAULO SÉRGIO (PT)
INST DE TELECOMUNICAÇÕES (PT)
| DE2809087A1 | 1979-09-06 | |||
| US20090216419A1 | 2009-08-27 | |||
| US20160116323A1 | 2016-04-28 | |||
| EP0393144A1 | 1990-10-24 | |||
| EP2685226A1 | 2014-01-15 | |||
| US3713338A | 1973-01-30 | |||
| US4354180A | 1982-10-12 | |||
| US4069838A | 1978-01-24 |
| In a particular embodiment, the developed sensor is applied integrally together with other optical and electrical monitoring systems and can be applied to groundwater or underground environments, to oil tanks and derivatives thereof and the like. The present description is of course in no way restricted to the embodiments presented herein and a person of ordinary skill in the art may provide many possibilities of modifying it without departing from the general idea as defined in the claims. The preferred embodiments described above are obviously combinable with each other. The following claims further define preferred embodiments. CLAIMS 1. Liquid level monitoring sensor comprising an optical fiber filament, said optical fiber filament comprising at least one segment arranged between the two ends of said filament, having at least one groove etched along the length thereof . 2. Sensor according to claim 1, wherein the spacing and depth of the grooves is adjustable. 3. Sensor according to claim 2, wherein the end of the filament opposite the end where the optical signal is injected is connected to a reflecting element. 4. Sensor according to claim 2, wherein the optical fiber filament comprises two segments, arranged between the two ends of the filament, wherein one of the filament segments has at least one etched groove and the other segment does not . 5. Sensor according to claim 4, wherein the non-grooved filament segment is associated with the end of the filament where the optical signal is injected, and the grooved filament segment is associated with the end of the filament where the optical signal is received. 6. Sensor according to claim 1, wherein the optical fiber filament is made of polymethylmethacrylate. 7. Sensor according to claim 1, wherein the optical fiber filament has a thickness of 1 mm and the grooves have a depth between 0.01 mm and 0.50 mm and are spaced apart between 1.00 mm and 200 mm. 8. Use of the sensor according to any claim 1 to 7, characterized in that it is integrated together with other optical and electrical monitoring systems and/or is applied to groundwater or underground environments, to oil tanks and derivatives thereof. |
SENSOR FOR MONITORING LIQUID LEVEL
Technical Field
The present application describes an optical fiber-based level sensor.
Background art
Documents EP0393144 Al, EP2685226 Al , US3713338 Al and US4354180 Al disclose optical sensors for liquid level measurements. Essentially, the sensors presented and currently available in the market make use of very complex forms, making the sensors an expensive product. As an example, the sensor disclosed in document US4069838 requires the arrangement thereof at a certain angle relative to the surface of the liquid and has only two measurement points, or fiber interruptions. In this case, only when the liquid reaches the level of these fiber interruption points does a variation in the optical signal occur and a change in the sensor signal.
An example of complexity is the patent US3713338 Al, which shows the need for 333 fibers for a resolution of 1.5 mm over a measurement range of 500 mm.
Summary
The objective of the optical fiber-based sensor developed is to measure variations in liquid levels in hostile or flammable environments, in locations of hard access or where the existence of electromagnetic fields may influence the operation of electronic sensors. Said sensor is therefore useful for applications in monitoring the level of flammable liquids, such as oil and derivatives thereof, as there is no risk of short circuit and consequent explosion.
The technology disclosed in the present application includes an alternative system for liquid level detection that uses polymer optic fiber with grooves along the length of the fiber, with a simple implementation of only one fiber, with no special mounting care, and at low cost. The measuring points may be of the order of tens and it does not require special care as far as the placement angle of the optical fiber, relative to the surface of the liquid is concerned.
General Description
The present application describes an optical fiber sensor for measuring the liquid levels in hostile and flammable environments, constructed from an optical fiber filament provided with grooves along its length. The type of fiber, whether made from plastic or glass, or the depth and/or spacing of the grooves, can be altered according to the intended resolution and application. In case of higher resolution in the measurement, for example in fuel tanks, it is possible to make a smaller grooves spacing. For coarser level measurements, greater spacing between grooves will provide a more stable sensor, but with lower resolution.
In one embodiment of the sensor developed, one end of the optical fiber filament is coupled to an optical signal injector device, and the opposite end to a signal receiving unit. In this configuration, the optical fiber filament is divided into two different segments: a first segment associated with the end connected to the optical signal injector, which is devoid of grooves, and whose length is such that it allows complying with the distance between the signal injector and the base of the container where the liquid is stored; and a second segment, associated with the end connected to the signal receiving unit, which has spaced grooves etched along said segment, and whose length is such that it allows complying with the distance between the base of the container and the signal receiving unit.
In another embodiment of the sensor developed, one end of the filament is connected to a reflecting element, for example an optical coupler, which redirects the radiation transmitted by the fiber, in the region of the grooves, to the photodetector present in a signal in ection and receiving unit, coupled to the opposite end. In this embodiment, the filament is provided with grooves along the entire length thereof, which extends from the signal injection and receiving unit, to the base of the container where the reflecting element is placed.
The introduction of grooves along the fiber filament is responsible for causing a loss in the optical signal received by the receiver unit due to the change in refractive index between the fiber core and the environment. Whenever the groove is filled by a material having a refractive index similar or closer to that of the fiber core, compared to that of air, such as for example water, the signal losses decrease. Thus, by inserting an optical fiber filament with these characteristics, the presence of the grooves allows detecting changes in the power of the optical signal transmitted along the filament, according to the rise of the liquid and consequent filling of each groove. Description of the Figures
For ease of understanding of the present application, figures are herein attached which represent exemplary embodiments which, however, are not intended to limit the technology herein disclosed.
Figure 1 shows the structure of the optical fiber-based liquid level sensor wherein reference numbers refer to:
1 - end of the optical fiber filament for connection to an optical signal injector;
2 - end of the optical fiber filament for connection to a signal receiving unit;
3 - segment of the optical fiber filament without grooves etched on the surface;
4 - segment of the optical fiber filament with grooves etched on the surface;
5 - groove .
Figure 2 shows a schematic of the fiber configuration by applying a reflecting element at the end of the filament, wherein reference numbers refer to:
4 - segment of the optical fiber filament with grooves etched on the surface;
5 - groove;
6 - reflecting element;
7 - optical signal injection and receiving unit.
Figure 3 shows the schematic of a practical application of the liquid level sensor in the oil industry, wherein reference numbers refer to:
4 - segment of the optical fiber filament with grooves etched on the surface;
7 - optical signal injection and receiving unit; 8 - liquid inlet;
9 - liquid collection system;
10 - liquid drain tube into the container;
11 - liquid container;
Description of the embodiments
With reference to the figures, some embodiments are now described in more detail, which are however not intended to limit the scope of the present application.
In one embodiment, one end (1) of the optical fiber filament is coupled to an optical signal injector device, and the opposite end (2) to a signal receiving unit. In this embodiment, the signal is injected at the end of the filament, runs through the first segment (3) without grooves, which extends to the base of the container (11) containing the liquid, and enters into the second segment (4), which is provided with grooves (5), runs through the respective fiber filament until it is collected, at the other end (2), by the data receiving unit for further processing.
In a further particular embodiment of the sensor, a reflecting element (6) is arranged at the end of the fiber filament (4), the optical signal being inserted and collected only by the opposite end, in the signal injection and receiving unit (7) .
In a particular embodiment, the liquid level measurement sensor developed is characterized by the use of an optical fiber composed of polymethylmethacrylate, having a thickness of 1 mm and with grooves having a depth of 0.01 mm to 0.50 mm, spaced apart between 1.00 mm and 200 mm.