CN104729628B - A kind of liquid level sensor and level measuring method based on optical fiber - Google Patents

Abstract

A liquid level sensor based on an optical fiber, the refractive index of the liquid to be detected is higher than that of the optical fiber, the sensor includes: a single-mode optical fiber for receiving test light, for receiving the test light output by the single-mode optical fiber and removing the coating layer The first multimode fiber with cladding and the second multimode fiber for receiving the test light output by the first multimode fiber and outputting it, the upper end of the single mode fiber is connected with the lower end of the first multimode fiber, the second The upper end of a multimode optical fiber is connected with the lower end of the second multimode optical fiber, the upper end of the second multimode optical fiber is the detection signal output end, the lower end of the single mode optical fiber is the test light input end, and the length of the first multimode optical fiber is greater than or equal to the To detect the maximum value of the liquid level, the optical axes of the single-mode optical fiber, the first multi-mode optical fiber and the second multi-mode optical fiber are on the same straight line. And a liquid level measurement method based on an optical fiber is provided. The invention effectively detects the liquid level of the liquid whose own refractive index is higher than that of the sensing optical fiber.

Description

A liquid level sensor and liquid level measurement method based on optical fiber

technical field

The invention relates to the technical field of optical fiber sensing, in particular to an optical fiber-based liquid level sensor and a measuring method.

Background technique

The optical fiber liquid level sensor is a sensor that uses optical fiber as the medium to measure the liquid level. It has important applications in the fields of fuel storage and biochemical processing. Compared with traditional sensors based on electrical methods, optical fiber-based sensors have the advantages of good electrical insulation, anti-electromagnetic interference, small size, and light weight, especially for flammable and explosive liquids. The advantages are more prominent. Generally, optical fiber-based liquid level sensors require optical fiber structures with special preparation processes, such as long-period fiber gratings, fiber Bragg gratings, and oblique fiber gratings, and are usually only suitable for measuring the liquid level of liquids whose refractive index is lower than that of the optical fiber. , but cannot measure gasoline, diesel and other liquids whose refractive index is higher than that of the sensing fiber.

Contents of the invention

In order to overcome the deficiency that the existing optical fiber liquid level sensor cannot be applied to the liquid whose own refractive index is higher than the refractive index of the sensing fiber, the present invention provides an optical fiber based Liquid level sensor and liquid level measurement method.

The technical solution adopted by the present invention to solve its technical problems is:

A liquid level sensor based on an optical fiber, the refractive index of the liquid to be detected is higher than that of the optical fiber, the sensor includes: a single-mode optical fiber for receiving test light, for receiving the test light output by the single-mode optical fiber, and The first multimode optical fiber with coating and cladding removed and the second multimode optical fiber used to receive the test light output by the first multimode optical fiber and output it, the upper end of the single mode optical fiber is connected to the first multimode optical fiber The lower end of a multimode optical fiber is connected, the upper end of the first multimode optical fiber is connected with the lower end of the two multimode optical fibers, the lower end of the single mode optical fiber is the test light input end, and the second multimode optical fiber The upper end of is the detection signal output end, the length of the first multimode optical fiber is greater than or equal to the maximum value of the liquid level to be detected, the single mode optical fiber, the first multimode optical fiber and the optical fiber of the second multimode optical fiber axes lie on the same line.

Further, the core diameter of the first multimode optical fiber is smaller than or equal to the core diameter of the second multimode optical fiber.

Further, the detection signal output terminal is connected to a liquid level detection module for detecting the power loss of the test light and determining the liquid level by referring to the pre-calibrated correspondence between the power loss and the liquid level.

A liquid level measurement method based on an optical fiber, said measurement method comprising the steps of:

(1) The test light enters from the single-mode optical fiber, propagates through the first multi-mode optical fiber immersed in the liquid and outputs from the second multi-mode optical fiber, detects the optical power at the output end of the signal, and compares it with the optical power of the test light to obtain Power loss;

(2) Referring to the preset corresponding relationship between the power loss of the test light and the liquid level, and according to the power loss of the test light, determine the liquid level of the liquid to be detected.

Further, the operator places the first multimode optical fiber of the sensor in the liquid to be tested, then measures the power of the test light output by the second multimode optical fiber of the sensor, and finally inquires the correspondence between the optical power loss and the liquid level through the operator The relationship determines the liquid level height of the liquid to be measured.

Or: fix the first multimode optical fiber in the sensor in the storage tank of the liquid to be detected, the change of the liquid level will directly cause the change of the output test optical power of the second multimode optical fiber, and the liquid level detection module receives the optical power measurement The obtained optical power loss and gives the liquid level value of the liquid.

The technical idea of the present invention is: abandoning the traditional measurement principle based on guided mode coupling or guided mode interference, and using a method based on leaky mode loss. By measuring the power loss of the test light transmitted through the single-mode optical fiber, the first multi-mode optical fiber and the second multi-mode optical fiber in turn, the liquid level of the liquid to be tested is determined, thus breaking the common optical fiber that cannot measure the liquid level of high refractive index liquid In addition, the sensor disclosed in the embodiment of the present invention only needs to use ordinary communication optical fiber and low-cost special multimode optical fiber with large core diameter for simple connection to realize accurate measurement of liquid level, so it is suitable for mass production and application.

The beneficial effects of the present invention are mainly manifested in: 1. Effective detection of the liquid level of the liquid whose own refractive index is higher than that of the sensing optical fiber; 2. Simple structure and low cost.

Description of drawings

Fig. 1 is a schematic structural diagram of a liquid level sensor based on an optical fiber;

Fig. 2 is the curve graph that test light output power loss changes with the liquid level of measured liquid in the liquid level measurement method based on optical fiber;

Fig. 3 is a flow chart of the optical fiber-based liquid level measurement method.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

Referring to Figures 1 to 3, a liquid level sensor based on an optical fiber is used to measure the liquid level of a liquid whose refractive index is higher than that of the optical fiber, as shown in Figure 1, including:

A single-mode optical fiber 100 receiving test light;

A first multimode optical fiber 101 connected to the single-mode optical fiber, receiving the test light output by the single-mode optical fiber and removing the cladding and coating in advance;

A second multimode optical fiber 102 connected to the first multimode optical fiber, receiving the test light output by the first multimode optical fiber and outputting it.

Wherein, the first multimode optical fiber can use a communication multimode optical fiber with a core diameter of 50 μm and a core refractive index of 1.46. The optical fiber length is 10 cm. The coating layer is stripped off and the cladding is removed using hydrofluoric acid. Here, the core diameter, refractive index and fiber length are preferably set, but are not limited to the fixed values. The length of the first multimode optical fiber is greater than or equal to the maximum value of the liquid level of the liquid to be measured, and the compactness of the sensor structure should be considered when determining the length.

The second multimode fiber may use a multimode fiber with a core diameter of 105 μm and a core refractive index of 1.46. Here, the core diameter and the refractive index are preferably set, but are not limited to the above fixed values.

The single-mode fiber is connected to the first multimode fiber without eccentricity, and the first multimode fiber is connected to the second multimode fiber without eccentricity.

The above connection method may be fusion splicing or other methods capable of connecting three sections of optical fibers.

The function realization process of the liquid level sensor is as follows:

When using this optical fiber-based liquid level sensor for liquid level measurement, the first multimode optical fiber is immersed in the measured liquid 103. At this time, the first multimode optical fiber is divided into two sections, and one section is immersed in the measured high refractive index. In the liquid with a high refractive index to be measured, the leaky waveguide is formed with the measured high refractive index liquid, supporting the leaky mode; the other section of the first multimode optical fiber is exposed in the air, and forms a guided waveguide with the air, supporting the guided mode.

Test light with a certain power is input from the single-mode fiber, and the test light is coupled to the leaky waveguide through the single-mode fiber. Since the leaky waveguide supports the leaky mode, the test light will cause power loss when it is transmitted in the leaky waveguide, and the loss is monotonously related to the length of the leaky waveguide, that is, the liquid level. Further, the remaining test light will be coupled into the guided waveguide and output by the second multimode optical fiber. Finally, the power loss of the test light output by the second multimode optical fiber is measured by an optical power meter.

Fig. 2 is a relationship curve of the output power loss of the test light with the liquid level of the measured liquid when the liquid level sensor in the embodiment disclosed by the present invention is used for liquid level measurement, and the refractive index of the measured liquid is 1.4769. It can be seen from the curve that when the liquid level of the liquid increases, the output power of the sensor decreases accordingly, and a one-to-one correspondence relationship is satisfied between the two. Therefore, after the power loss of the test light output by the liquid level sensor is measured, the liquid level of the liquid to be measured can be determined by querying the correspondence table between the power loss and the liquid level.

It should be noted that the output power requirement of the test light described in this embodiment is that it can still be accurately measured by the optical power meter after the loss of the liquid level sensor. With reference to the measuring range and accuracy of the existing common optical power meter, this embodiment preferably selects the test light whose output power is between 0dBm--20dBm. It is not limited to this in practical applications, and the output power used can be determined according to specific conditions.

In the optical fiber-based liquid level sensor disclosed in this embodiment, the optical fibers used are ordinary single-mode optical fibers, ordinary multi-mode optical fibers and special multi-mode optical fibers, and only the single-mode optical fiber, the first multi-mode optical fiber and the second Multimode optical fibers can be connected sequentially without complex photolithography technology, so this optical fiber-based liquid level sensor has the advantages of low cost and easy fabrication compared with other liquid level sensors that measure liquids with a higher refractive index than ordinary optical fibers. The advantage of simplicity.

Further, the single-mode optical fiber in this embodiment may be a single-mode communication optical fiber, and the first multi-mode optical fiber may be a multi-mode communication optical fiber. For the convenience of production, a relatively common communication optical fiber is used here, but the use of communication optical fibers is not limited. .

Further, the second multimode fiber in this embodiment is a multimode fiber with a core diameter of 105 μm. Here, in order to reduce the coupling loss of the sensor, it is not limited to use the multimode fiber with this core diameter parameter.

Corresponding to the sensor in the above embodiment, the present invention also discloses a liquid level measurement method based on optical fiber, which is used for the sensor, as shown in Figure 3, including the steps:

S301: Measure the power loss of the test light that enters from the single-mode optical fiber, propagates through the first multi-mode optical fiber immersed in the liquid, and is output from the second multi-mode optical fiber;

S302: Referring to the preset corresponding relationship between the power loss of the test light and the liquid level, determine the liquid level of the liquid according to the power loss of the test light.

There are two application scenarios here: first, by manual measurement, that is, the operator places the first multimode fiber of the sensor in the liquid to be tested, then measures the power of the test light output by the second multimode fiber of the sensor, and finally The liquid level height of the liquid to be measured is determined by the operator inquiring about the corresponding relationship between the optical power loss and the liquid level; secondly, the first multimode optical fiber in the sensor is fixed in the storage tank of the liquid to be measured, and the change of the liquid level will directly As a result, the output test optical power of the second multimode optical fiber changes, and the processor receives the optical power measured by the optical power meter, and then gives the liquid level value of the liquid.

The optical fiber-based liquid level testing method disclosed in the present invention is based on the principle of leaky mode loss in a leaky waveguide, and realizes that only ordinary single-mode and multi-mode optical fibers can be used to measure the liquid level of liquids whose refractive index is higher than that of ordinary optical fibers , while ensuring the measurement accuracy, the measurement cost is reduced.

Further, the test light described in this embodiment is: a laser that matches the wavelength parameters of the single-mode fiber and the multi-mode fiber. For example, the test light matching the optical fiber used in the liquid level sensor in the previous embodiment is a laser with a wavelength of 1550 nm. The use of a laser guarantees the accuracy of ordinary power meter measurements.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same or similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. a kind of liquid level sensor based on optical fiber, it is characterised in that：The refractive index of liquid to be detected is higher than the refractive index of optical fiber, The sensor includes：For receiving the single-mode fiber of test light, the test light for receiving the single-mode fiber output and going Except the first multimode fibre of overlay and covering and for receiving the test light of the first multimode fibre output and outputting it The second multimode fibre, the upper end of the single-mode fiber is connected with the lower end of first multimode fibre, first multimode The upper end of optical fiber is connected with the lower end of two multimode fibre, and the lower end of the single-mode fiber is test light input end, described The upper end of second multimode fibre is detection signal output part, and the length of first multimode fibre is more than or equal to the liquid to be detected The maximum of body fluid position, the single-mode fiber, the first multimode fibre and the optical axis with the second multimode fibre are located along the same line.

2. the liquid level sensor as claimed in claim 1 based on optical fiber, it is characterised in that：The fibre core of first multimode fibre Diameter is less than or equal to the core diameter of the second multimode fibre.

3. the liquid level sensor as claimed in claim 1 based on optical fiber, it is characterised in that：The detection signal output part is with using In detection test light power attenuation and determine liquid with reference to the optical power loss and the corresponding relation of liquid level demarcated in advance The level sensing module of position is connected.

4. a kind of be used for the level measuring method of the liquid level sensor as claimed in claim 1 based on optical fiber, it is characterised in that： The measuring method comprises the following steps：

(1) test light is entered by single-mode fiber, the first multimode fibre through immersing in the liquid is propagated and from the second multimode light Fibre output, the luminous power of measurement detection signal output part, calculates and obtains power attenuation more afterwards with the test optical power ratio of input；

(2) with reference to default test optical power loss and the corresponding relation of liquid level, according to the power attenuation of the test light, it is determined that The liquid level of liquid to be detected.

5. level measuring method as claimed in claim 4, it is characterised in that：Operator puts the first multimode fibre of sensor It is placed in testing liquid, the power of the test light by the second multimode fibre output of sensor is then measured, most afterwards through operator Corresponding relation between inquiry optical power loss and liquid level determines the liquid level of testing liquid.

6. level measuring method as claimed in claim 4, it is characterised in that：The first multimode fibre in sensor is fixed on In the storage tank of liquid to be detected, the change of liquid level will result directly in the change of the second multimode fibre output test luminous power, liquid The optical power loss that measures of position detection module received optical power and the level value for providing liquid.