JPS58127149A - Spectral analyzing device - Google Patents

Abstract

PURPOSE:To provide a simple structure spectral analyzing device which eliminates division, by a method wherein a lock-in amplifying output is held in a constant manner through negative feedback of the lock-in amplifying output to directly fetch a ratio of a differential collection to a collecting power. CONSTITUTION:Laser light from laser L is collected by a collecting element D through a gas cell GC and is processed by a self-gain adjusting amplifier 4 and lock-in amplifiers LA1 and LA2 to produce a collecting power and differential collecting power. By means of the output of the amplifier LA1, negative feedback of an amplifier 4 is controlled to maintain the amplifier LA1 in a constant output, and an output corresponding to a ratio of the differential collecting power to the collecting power is fetched directly from the amplifier LA2. This eliminates a dividing part, which results in forming a simple structure spectral analyzer.

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention utilizes resonance absorption of infrared rays, and calculates the −th order differential ^^
The present invention relates to a spectroscopic analysis method for performing differential measurement, and particularly to a spectroscopic analysis device that does not require division of differential received light power/received light power when performing differential measurement.

(To) Background of the Technology In recent years, with the rapid development of chemical industry technology, the number of processes in which specific substances are treated in a gas atmosphere of a predetermined concentration has increased, but during this treatment process, There is a growing need to monitor the concentration of gases as analytes to be exposed to the above substances.

In such a case, the above gas (or aerosol/I/
) will need to be sampled appropriately and tested.

On the other hand, recently, light sources, especially lasers, have been developed for this concentration measurement, and laser light of a specific wavelength (infrared rays) is transmitted through the target gas to measure the amount of laser light absorbed by the gas. , technology for quantifying gas concentrations is now being established.

(Q) Prior art and problems Based on these considerations, the configuration shown in Figure 1 was created, in which gaseous substances, that is, gases sampled during Ganuse/I/GC (hereinafter, for convenience, only gases are ) is enclosed, and the light emitted from the laser L follows the optical path H indicated by the arrow and enters the gas 7/L/GC. This light is attenuated due to absorption by the gas in the gas cell GO, so the amount of light coming out of the gas cell GO is decreasing, but this light is photoelectrically converted by the light receiving element and forwarded. The concentration of the gas is expressed as an electrical signal at the output terminal of the stationary amplifier A, and the concentration of the gas is compared when there is no gas, when the gas cell is empty, and when it is full of gas as described above. was being determined. However, in Fig. 1, REG is a power supply whose output changes depending on the settings, O20 is a sine wave generator, S is a superimposition device that superimposes the output of the sine wave generator O8C on the output of the power supply REG, and l is a The laser drive power supply is the laser drive power supply, OH is the optical chopper, and the trench cutter is the laser drive current.

To monitor the above gas concentration, the electrical signal appearing at the output terminal of preamplifier A is introduced into the first and second lock-in amplifiers LAI, LA2, respectively, and is connected to a sine wave generator via paths A and A. ○Signal from SC and chopper CH
Each of the signals from the lock-in amplifier LAI
, LA2. In this way, the second lock-in amplifier LA2 works in the differential mode, while the first lock-in amplifier LA1 works in the normal mode.
Each lock-in amplifier LA1. Differential received light power P and received light power P are output to each output of LA2, respectively.

By the way, in order to perform differential measurement, it is necessary to find the quotient of these two outputs P' and P, so if these outputs are respectively introduced into the two inputs of the divider V, the output 2 will have Pl. The value '/P appears, and it becomes possible to perform measurements without fluctuations in the amount of infrared rays absorbed by the gas.

However, if a commercially available divider is used as a divider, it can be made compact, but the dynamic range is extremely narrow, and if the division accuracy is not good, problems will always arise. For that reason, the above P.

The above problem can be solved by using a computer to perform division after passing each quantity P' through an A/D converter, but it often has the disadvantage that the overall structure of the device becomes large.

(C1) Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks of the conventional art. The purpose of this invention is to provide a simple spectroscopic analysis device that does not require

(e) Structure and object of the invention According to the present invention, an optical path passing through a space in which a gaseous substance to be measured exists is formed between a wavelength tunable laser and a light receiving element, and the light receiving element performs photoelectric conversion. A preamplifier for amplifying the received signal and two lock-in amplifiers connected to the rear stage of the preamplifier are provided, and the concentration of the substance to be measured is measured from the ratio of the differential received light power and the received light power. , Negative feedback is provided to the preamplifier from the output terminal of one lock-in amplifier corresponding to the received light power, and negative feedback is provided to the output terminal of the other lock-in amplifier corresponding to the ratio of the differential received light and the received light power. This is achieved by providing a spectroscopic analyzer characterized in that it directly outputs several signals.

(f) Embodiment of the Invention FIG. 2 shows an embodiment of a circuit diagram of a spectroscopic analyzer according to the present invention, and the same parts as in FIG. 1 are denoted by the same reference numerals.

The difference between the circuit diagram in FIG. 2 and that in FIG. A negative feedback path C is provided which is separated from the 92 output terminals of the lock-in amplifier LA2 and connected to the control terminal Q of the automatic gain adjustment amplifier 4.

Therefore, a minute alternating current signal is superimposed on the drive current flowing to the laser L, and as a result, frequency modulation is applied and photoelectric conversion is performed by the photodetector through the laser channel CH, gas cell GC, and is amplified by the automatic gain adjustment type amplifier 4. This signal appears at the output terminal P1 of the first lock-in amplifier LAI and is again applied to the control terminal Q of the automatic gain control amplifier 4 via the path C, so that it appears at the point Pl. The received light power P is kept at a constant value.

Therefore, the differential received light power is the pair of received light power, that is, P/
Since the received light power P in the denominator at P is normalized to a constant value, in order to measure the gas concentration, the output voltage at point P2, that is, the output terminal 3 of the device in Fig. 2, is drawn on an XY recorder, etc. There is no need to calculate P'/P every time a measurement is made.

By the way, during measurements using this device, the automatic gain adjustment type amplifier 4
Strictly speaking, the received light power P1, that is, the voltage at point R in FIG. 2 changes. However, if the feedback lid to the automatic gain adjustment type amplifier 4 is enlarged to reduce fluctuations in the received light power P, and if this fluctuation is suppressed, measurement can be performed with higher accuracy.

(2) Effects of the Invention As explained in detail above, when using the spectroscopic analyzer of the present invention, there is no need to divide P/P when detecting gaseous substances by differential measurement. Since it can be easily measured, great practical effects can be expected.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a block diagram of a main part of a conventional spectroscopic analyzer, and FIG. 2 is a diagram showing a block diagram of a main part of a spectroscopic analyzer according to the present invention. In the drawing, ■ is the laser drive power supply, and 2 is the dividing machine ■
8 is the output terminal of the lock-in amplifier LA2,
D is a light receiving element, GO is a gas cell, CH is a chopper, H is an optical path, ■ is a laser drive current, L is a laser, and C is a negative feedback path.

Claims (1)

[Claims] A preamplifier that forms an optical path that passes through a space where a gaseous substance to be measured exists between the wavelength-tunable laser and the photodetector, and amplifies the signal photoelectrically converted by the photodetector, and a preamplifier that is located downstream of the preamplifier. In a configuration that includes two connected lock-in amplifiers and measures the concentration of a substance to be measured from the ratio of the differential received light power and the received light power, the output of one lock-in amplifier corresponding to the above-mentioned received light power is maintained constant. A feedback path that provides negative feedback to the preamplifier is provided from the output terminal of the lock-in amplifier, and a signal corresponding to the ratio of the differential received light and the received light power is directly sent to the output terminal of the other lock-in amplifier. A spectroscopic analysis device characterized in that it can be taken out.