RU172412U1 - METHANE CONCENTRATION METER MULTI-CHANNEL FIBER OPTIC - Google Patents

Abstract

The utility model relates to optical diagnostic devices. A multichannel fiber-optic methane concentration meter determines the concentration of methane in air in optical sensors connected via independent fiber-optic lines by transmitting monochromatic optical laser radiation through them, whose wavelength varies according to a given periodic law. In this case, the laser parameters are set through feedback, organized by removing part of the radiation through a fiber optic splitter and passing it through a hermetically sealed adjustment cell with methane, which is part of the head unit of the device. In addition, radiation from independent sensors is received through sequential polling and analysis of signals received from an array of photodetectors, the number of which corresponds to the number of measuring channels, taking into account the channel of the reference signal and the channel of a calibrated cell with methane. The technical result consists in increasing the sensitivity of measurements, minimizing the number of system elements. 2 s.p. f-ly, 3 ill.

Description

The utility model relates to optical diagnostic instruments for measuring methane concentration in air. The utility model can be used to ensure fire safety in residential and industrial premises, as well as to control the degree of explosion hazard of objects.

State of the art

A number of fiber optic systems for remotely measuring methane concentration are known in the art. For example, a system consisting of a light source, a mechanical modulator, an optical fiber line, a gas cell, and an optoelectronic signal reception system [“Remote Fiber-Optic Methane Monitor”, T.N. Dubaniewicz, J.Ε. Chilton, "Report of investigations No. 9407", 1992].

Also known are fiber-optic monitoring systems for underground coal mines, consisting of a head multifunctional unit and an extensive network of fiber optic passive sensors, as well as fiber-optic cable infrastructure ["Development and utilization of fiber optic-based monitoring systems for underground coal mines", S.M. Aminossadati, M. Amanzadeh, M.S. Kizil, T. Liu, “Coal Operators Conference”, 2014].

Also known is an experimental sample of a fiber optic methane detector based on photonic crystal fibers (Mettler-Toledo International Inc), consisting of a radiation source, a gas chamber, a pressure meter and a methane supply system, an optical fiber line, a sensitive photonic crystal fiber, an optical detector and a processing device .

Also known is the system described in ["Fiber optic methane gas detection system", Hitachi cable review No. 25, august 2006], adopted as a prototype. The system for remote measurement of methane concentration in air is made in the form of separate blocks of an optical fiber detector and an optical fiber adder. The disadvantage of this technical solution of the prototype is the lack of precision tuning and retention of the laser wavelength near the peak absorption of methane.

The common disadvantages of all of these known systems are the limited applicability in residential buildings and industrial premises, accompanied by high cost and complexity in operation.

The closest analogue of the proposed technical solution is a fiber-optic gas analyzer [patent application 94030252/25 of 08.16.1994], which contains sequentially mounted and optically coupled emitters, an input optical fiber, a multi-pass cell consisting of three spherical mirrors, an output optical fiber, a block registration and processing of information. The disadvantage of this system is the presence of a large number of mirrors and additional elements, which greatly complicates the alignment of the system and its cost.

Utility Model Disclosure

The present utility model is based on the solution of the problem aimed at creating a commercially available high-sensitivity fiber methane concentration meter that provides control of methane concentration in residential and industrial premises.

The technical result obtained by using the proposed technical solution is to significantly reduce the size of the system, minimize the number of system elements, there is no need to maintain a constant temperature of circuit elements, increase the sensitivity of measurements and expand the range of equipment on the market.

To solve this problem, a multichannel fiber-optic methane concentration meter is proposed that measures methane concentrations in air in optical sensors connected via independent fiber-optic lines to it by transmitting monochromatic optical laser radiation through them, the wavelength of which varies according to a specified periodic law; in this case, the laser parameters are set via feedback, organized by removing part of the radiation through a fiber optic splitter and passing it through a hermetically sealed adjustment cell with methane in the head unit of the device; in addition, radiation from independent sensors is received by means of sequential polling and analysis of signals received from an array of photodetectors, the number of which corresponds to the number of measuring channels, taking into account the channel of the reference signal and the channel of a calibrated cell with methane. The head unit can be installed in a telecommunication rack.

Brief Description of the Drawings

The essence of the proposed technical solution is illustrated by figures.

In FIG. 1 is a schematic diagram of a multi-channel fiber optic methane concentration meter.

In FIG. Figure 2 shows the time dependences of the laser currents (upper), reference photodetector (middle), and signal photodetector (lower) in the presence of methane.

In FIG. Figure 3 shows the dependence of the depth of the dip of the current curve of the signal photodetector on different concentrations of methane located in the measuring volume of the passive optical sensor (the current graph of the alignment cell is similar).

Utility Model Implementation

The methane concentration meter multichannel fiber optic in FIG. 1 contains a semiconductor laser with distributed feedback with an optical fiber output 1 and a control and thermal stabilization unit 2 located under it, an optical splitter 3 connected to a photodetector of the reference signal 4 and an optical splitter 5, which, in turn, is connected to quotation components: a cuvette with methane 6 and a photodetector 7, and fiber optic lines 8 are connected to passive optical sensors and methane 9, which are connected to signal photodetectors 10 mounted on the photodetector board 11, a signal line with which is used by the FPGA card 12; all components of the device, except 8 and 9, are placed in the housing 13.

A multi-channel fiber meter methane concentration meter, the circuit diagram of which is shown in FIG. 1, works as follows.

A distributed feedback semiconductor laser with a fiber optic output 1 with a central wavelength of ~ 1654 nm, controlled by a control and thermal stabilization unit 2, emits optical radiation modulated in amplitude and wavelength by tuning in current over a specified range during thermal stabilization. The tuning range of length overlaps the spectral absorption peak of methane (6055-6059 cm ^-1). The laser radiation passes through a fiber optic splitter 3, where part of it is diverted to the reference photodetector 4, while most of the radiation falls on the splitter 5, where it is divided into n channels in equal proportions. One of the channels is closed to an adjustment cell with methane 6, and the radiation passing through the cell is transmitted to the quotation photodetector 7. The radiation passes through optical fiber lines 8 through the passive optical sensors of methane 9, the signal is transmitted to the signal photodetectors 10, which are interrogated by the photodetector board 11, signal processing is carried out by FPGA 12. The FPGA algorithm is configured so that the peak of methane absorption in the adjustment cuvette 6 always falls on a certain time interval within each th laser modulation period. In the case of a shift of this peak, the feedback performs precise adjustment of the laser according to current and / or temperature by means of an integrated Peltier element. This provides constant control of the laser wavelength and, as a result, high measurement accuracy. The methane concentration is determined by the relative depth of the dip in the signal photodetector current versus methane concentration in the measuring volume of the passive optical sensor.

The calibration of the output values can be done by measuring the concentration of calibration gas mixtures. The measurement results can be displayed through the built-in liquid crystal display and other means of indication, as well as through a remote operator terminal. The head unit of the device can be installed in a standard telecommunications rack size 19 '. The passive methane sensor is based on an optical circuit using known reflective elements (mirror, reflector).

The proposed technical solution provides the claimed technical result, namely, a significant reduction in the size of the system, minimizing the number of system elements, the lack of the need to maintain a constant temperature of circuit elements, increasing the sensitivity of measurements and expanding the range of equipment on the market.

Claims (3)

1. Methane concentration meter is a multi-channel fiber-optic meter, characterized in that it provides a methane concentration measurement in air in passive optical sensors connected to independent optical fiber lines by transmitting monochromatic optical laser radiation through them, the wavelength of which varies according to a specified periodic law, while laser parameters are set through feedback, organized by removing part of the radiation through fiber optic the tweeter and passing it through a hermetically sealed adjustment cuvette with methane as part of the head unit of the device, in addition, radiation from independent sensors is received by sequential interrogation and analysis of signals received from an array of photodetectors, the number of which corresponds to the number of measuring channels taking into account the reference signal channel and channel calibrated cell with methane. 2. Methane concentration meter multichannel fiber optic according to claim 1, characterized in that the design of passive optical sensors uses a two-pass optical circuit, which provides increased sensitivity and compact size of the sensor. 3. Methane concentration meter multichannel fiber optic according to claim 1, characterized in that the head unit is installed in a telecommunication rack.

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