Optical fiber methane sensing system based on fiber core mismatch

Abstract

The invention discloses an optical fiber methane sensed system based on mismatch of core radii, which comprises an infrared light source, a coupler, a measuring system, a reference system and a computer. The measuring system comprises an optical fiber sensor coated with a methane sensitive layer, a test gas chamber, a switch valve, a mass flow controller and a photo detector; the reference system comprises another optical fiber sensor coated with methane sensitive layer and a photo detector. The front end of the optical fiber sensor of the reference system are coupled with the front end of the sensor of the measuring system via the coupler in order to be connected with the infrared light source and the rear ends of the reference system and the measuring system share the computer. The sensor is an optical fiber sensor of core radii mismatch, which is formed by welding two ends of a section of a single mode fiber with a multi-mode fiber; the methane sensitive layer containing supermolecules of cage structure is coated on the surface of the clad of the single mode fiber; the single mode fiber and multi-mode fiber are both common standard communication optical fiber. When the methane gas to be tested contacts the sensitive layer, the refractive index changes and the concentration of the methane gas to be tested can be obtained according to the relative change of the output uniformazation light power of the sensor. The sensed system is simple in structure, low in cost, high in flexibility and fast in response.

Description

technical field [0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a fiber core mismatch type optical fiber sensing system for obtaining methane concentration. Background technique [0002] Methane is a flammable and explosive gas, and it is the main component of mine gas, accounting for about 83-89%. In my country's coal mine safety accidents, gas explosions account for more than 50% of the casualties in all major accidents, and are known as the "number one killer" of coal mine accidents. Methane is also the main component of natural gas, biogas and various liquid fuels. It is an important industrial raw material and daily life gas. The lower limit of explosion in the atmosphere is 5.3%, and the upper limit is 15.0%. At the same time, methane is still one of the main components causing the "greenhouse effect", and the long-term corrosion of urban gas pipelines is also a major hidden danger to urban safety. Therefore,...

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Problems solved by technology

However, the sensing system still has the following deficiencies: (1) The sensing system uses PCS optical fiber, which has problems such as large long-distance transmission loss, mismatch with ordinary standard communication optical fibers, high cost, and difficulty in engineering application; The thickness of the methane-sensitive film of the cage-shaped supramolecule is as high as 5 μm, which makes it difficult for methane molecules to diffuse and migrate in the sensitive film, and the sensor responds slowly and takes a long time to recover; (3) although the proposed sensor system output Optical power is normalized as a benchmark, but it only has a measurement system, but no reference system, and it is difficult to compensate for optical signal fluctuations caused by environmental factors such as light source, power supply, temperature and humidity

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