SU1187033A1 - Gas analyser - Google Patents

Abstract

A GAS ANALYZER containing optical conjugate radiation sources, made in the form of two LEDs emitting at different wavelengths, an optical cell with input and output windows and a photodetector associated with an electronic signal isolation circuit, characterized in that, in order to increase accuracy and sensitivity measurements due to more complete use of the radiation fluxes of the LEDs, the latter are additionally equipped with parabolic reflectors, the photodetector is additionally equipped with a concave mirror, located on the side of its photosensitive site, and the entrance window of the optical cell is made in the form of a holographic diffraction grating, while the LEDs with reflectors are set relative to the optical axis of the gas analyzer at angles that ensure that the diffraction angle is zero at the incidence of the LED radiation on the diffraction grating.

Description

The invention relates to optical instrumentation and can be used to create gas analyzers, in particular an infrared methane gas analyzer.

The purpose of the invention is to improve the accuracy and sensitivity of measurements due to more complete use of LED radiation fluxes.

Fig, 1 shows a diagram of a gas lysator; in fig. 2 shows the radiation pattern of the LEDs.

The gas analyzer contains a power supply unit 1, from which a worker 2 and a power supply are fed with a frequency of 1 kHz. filament 3 emitting LEDs placed in the foci of two parabolic mirror reflectors 4 of radiation, transmitting a holographic diffraction grating 5, directing the radiation of LEDs into an optical cell 6, designed to specify the absorbing volume of the test gas, behind which is located a concave spherical mirror 7 fixing the radiation light-emitting diodes on the photocell 8. A two-channel amplifier 9, the device 10, a signal comparison device 10, are designed to process the signals of the photodetector 8 and output their ratio to providing device 11.

Gas analyzer works as follows.

The power supply unit 1 is supplied with a frequency of 1 kHz and a phase shift of m / 2 rectangular supply pulses to the LEDs, the radiation of which is spectrally separated by the wavelength, the radiation of the working LED 2 coinciding, and the comparative 3 does not coincide with the absorption band of the gas under study.

The radiation pattern of the LEDs has a petal shape (Fig. 2), therefore, the LEDs are placed at the foci of parabolic mirror reflectors 4, which makes it possible to create a highly parallel intense flux of infrared radiation of the LEDs and direct it towards the specified angles С |, and Cf (comparative and working LEDs, respectively) to the input window of the optical cell, made in the form of a protruding holographic diffraction grating 5. Parabolic mirror reflectors are set so that their optical The hard axes are located at angles Lp and (p, which are selected from the diffraction equation.

. The feature of the optical scheme is that the transmission diffraction holographic grating is produced with such a number of grooves that at given angles of incidence of the radiation (tp and IP y) the diffraction angle (y) is zero.

After diffraction at the entrance window, the radiation passes through the optical cuvette 6, is focused by the concave mirror 7 to the photosensitive area of the photodetector, 8, which produces electrical signals, which are separated in a two-channel amplifier in a two-channel amplifier by two channels and amplified. The signal comparison device 10 outputs their relationship to the indicating device 11.

A specific example of a gas analyzer is a model for determining the pre-explosive concentration of methane in which two emitting LEDs are used: a working one with a emission wavelength of 3, 32 µm, which coincides with the maximum absorption of methane, and a comparative one with a emission wavelength of 3.80 µm, which emits in where methane does not absorb.

The half-width of the LED emission line is 0.30 µm. Parabolic mirror reflectors of radiation (the shape of the surface is a paraboloid of rotation of 30 x) allows to obtain a high-quality parallel infrared beam, which gives a 29-fold increase in the signal intensity from the LED. After diffraction from a holographic glass grid As S, the intensity of the signal from the LED in the first diffraction order is 85% of the incident on the grating. The angles of incidence cf, (for, 3.32 µm) and 2 (for 3.80 µm) are 30 and 35 °, respectively, with the number of strokes of the transmitting holographic diffraction grating 150 lines / mm, which allows, after diffraction, beams of both wavelengths to direct along one optical axis along the cuvette.

Optical signals from both LEDs, focused by a spherical mirror (40 mm in diameter), are registered by the SF4-12 photodetector with a receiving area of 1x1 mm.

Claims (1)

A GAS ANALYZER containing optical coupled radiation sources made in the form of two LEDs emitting at different wavelengths, an optical cuvette with input and output windows, and a photodetector connected to an electronic signal separation circuit, characterized in that, in order to increase the accuracy and sensitivity of measurements due to a more complete use of LED radiation fluxes, the latter are additionally equipped with parabolic mirror reflectors, the photodetector is additionally equipped with a concave mirror, the side of its photosensitive area, and the entrance window of the optical cuvette is made in the form of a holographic diffraction grating, while the LEDs with reflectors are mounted relative to the optical axis of the gas analyzer at angles that provide a diffraction angle equal to zero when the LED radiation falls on the diffraction grating. KOEEV o © o