SU1176220A1 - Double-channel gas analyser - Google Patents

Abstract

A TWO-CHANNEL GAS ANALYZER containing optically coupled radiation source with a collimator, a switch modulator, measuring and reference optical channels, each of which contains an optical filter, focusing optics, a radiation receiver and an electrical signal processing circuit, containing 1: 1a amplifier, one of the inputs which is connected to the output of the radiation receiver, and the output to the first input of the detector, to the other input of which is connected a synchronization circuit connected to the modulator switch, an automatic Adjusting the gain, the output of which is coupled to another input of usshshtel, characterized in -that,. In order to improve measurement accuracy due to the fullest use of the radiation power of the source, the electrical signal processing circuit further comprises an output circuit, even harmonics of the radiation receiver signal, one of the inputs of which is connected to the amplifier output, the other input from the output of the synchronization circuit, and the output — with an automatic gain control unit vhbd; when the modulator-switch is designed in such a way that it ensures that even-harmonic switching frequencies are present in the signal of the radiation receiver ii. Oh with

Description

The invention relates to a measurement technique and can be used to measure the content of the selectively absorbed gas components of the atmosphere. The purpose of the invention is to improve the measurement accuracy due to the fullest use of the power of the source radiation flux. Figure 1 shows the functional circuit diagram of the device for local measurements, option; Fig. 2 is an optical diagram of a remote gas analyzer option in Fig. 3 beam-switching modulator for the most high-aperture gas analyzer; figure 4 - the dependence of the flow incident on the photodetector, from time to time in the absence of the test gas in the measuring channel; Fig. 3 shows the dependence of the flow falling on the photodetector on time in the presence of the gas under study in the measuring channel. The device for local measurements (Fig. 1) contains a radiation source 1 located in the focus of the collimator 2, a switch-modulator 3 which in the simplest case is a disk with holes, a measuring cell 4 of the measuring channel with the gas mixture under study, an optical filter a reference channel, consisting of a cuvette 5 with a known amount of gas, identical to the measured component of the gas mixture being studied, and a spectral filter 6, which passes radiation only in the absorption band of the measured component and is simultaneously optical SCIM filter of measuring channel; screen 7 with holes coaxial with windows cuvette 4 and 5, fixing lens 8, photodetector 9, amplifier 10, detector 11, even-harmonics extraction circuit 12 of the amplifier signal, AGC block 13 and synchronization circuit 14 associated with modulator switch 3. Section A-A shows how switch-modulator switch 3 can be made and positioned so that its holes, while rotating, alternately pass radiation through cuvettes 4 and 5. Cell 4 may be absent; the studied components in the air surrounding the device, In the remote version (FIG. 2), the cuvette 4 is also absent. The lighting system in this case consists of a lighting lens 15 and a field diaphragm 16 located in its focus and focus of the collimator 2. The variants of the proposed device can be multicomponent. In this case, between the collimator and the focusing lens, there are as many measuring and reference cells, optical filters, etc., as the components are examined — the number of focusing objectives, photodetectors, and electronic circuits is also equal to the number of components under study. When measuring the amount of unstable components, such as ozone, or components with almost continuous absorption spectra, such as water vapor and carbon dioxide, the optical filter of the reference channel is a spectral filter that transmits radiation outside the absorption bands of these components, and the spectral filter is an optical filter. only measuring channel. In better use of flow in multicomponent versions of the device, it is advisable to use a collimator 2, the cross section of which is equal to the cross section of each of the compared streams (Fig.4), and a switch modulator consisting of a movable breaking mirror 18 and fixed breaking mirrors 19, the number of which is equal to the number of optical channels, i.e. double the number of components studied. The device works as follows (figure 1). The flow from the radiation source 1 is converted by the collimator 2 into a quasi-parallel flow, which partially passes through the opening of the rotating disk of the modulator-switch 3 and the apertures of the screen 7 when they overlap with the holes of the modulator-switch 3. On the cuvette 4 of the measuring channel through which it passes the gas mixture under study, and the reference cell 5 filled with a known amount of gas identical to the measured one, are modulated in anti-rim3

There are radiation fluxes that are focused by the lens 8 onto the photodetector 9 with a spectral filter 6 transmitting radiation in the absorption band of the measured gas. The amplifier 10 amplifies the variable component of the signal of the photodetector 9, the detector 11, controlled by the synchronization circuit 14 connected to the modulator switch 3, selects the first harmonic of the switching frequency, and its output voltage characterizes the presence of the measured gas in the mixture. Circuit 12 extracts from the signal of the amplifier any even harmonic of the switching frequency, while circuit 12 is also controlled by timing circuit 14. The AGC block 13 operates in such a way that the voltage of the even harmonic of the switching frequency applied to it is kept constant. In this case, the gain of amplifier 10 is inversely proportional to the amplitude of the same even harmonic in the signal of the photodetector 9, and the voltage at the output of the detector 11. is proportional to the ratio of the amplitude of the first harmonic of the signal of the photodetector to the amplitude of the selected even harmonic and therefore does not depend on the source brightness, non-selective medium transmission optical details, sensitivity of the photodetector and the type of nonlinearity of the light characteristics of the photodetector.

The remote option (Fig. 2) works in a similar way, with the only difference that the test media is not passed through the measuring cell and is not in the volume of the device, but is located between devices 762204

rum and any distant light source, the image of which was obtained using the illuminating lens 15 and diaphragmically field

5 aperture 16.

The device operates similarly in the case when instead of the reference cell 5 in the reference channel there is a spectral filter 17,

Allowing radiation outside the absorption band of the measured gas, and the spectral filter 6 is the optical filter of the measuring channel only. The high-aperture modulator version

5 switch (fig.Z) commutes

all the flow past the diaphragm 16, and not part of it. The flow from the collimator 2 is directed by moving the movable mirror 18 on the fixed ones.

0 breaking mirrors 19, each of which directs the stream falling on it either into the reference or into the measuring channel through the openings of the screen 7.

5 In the absence of measurable

the components in the research environment; the flows that pass through the reference and measuring channels are equal, and the signal of the photodetector during the rotation of the module 0 of the torus switch 3 is missing, which has a frequency equal to the switching frequency (Fig. 4). If there is a measurable component in the medium under study, the flow past the measuring channel in all variants of the device becomes smaller than the flow past the reference channel. The signal of the receiver appears the component of the switching frequency,

Q which has an amplitude that is functionally related to the amount of the component being measured (Fig. 5).

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Claims (1)

A TWO-CHANNEL GAS ANALYZER containing optically coupled radiation source with a collimator, a modulator-switch, measuring and reference optical channels, each of which contains an optical filter, focusing optics, a radiation receiver and an electrical signal processing circuit containing an amplifier, one of the inputs of which is connected to the output radiation detector, and the output with the first input of the detector, to the other input of which is connected a synchronization circuit associated with a modulator-switch, an automatic control unit gain lines, the output of which is connected to another input of the amplifier, characterized in that, that. in order to increase the accuracy of measurements due to the fullest use of the power of the radiation flux of the source, the signal processing circuitry further comprises a circuit for extracting the even harmonics of the signal from the radiation receiver, one of the inputs of which is connected to the amplifier output, the other input to the output of the synchronization circuit, and the output with the input of the automatic gain control unit, while the modulator-switch is made in such a way that ensures the presence of even harmonics of the switching frequency in the signal of the radiation receiver. SU „1176220