JPS5972048A - Absorptiometer - Google Patents

Abstract

PURPOSE:To perform measurement not affected by variation of a light source including batch measurement with a simple constitution by fixing and controlling gains of a detection system at the time of detecting the zero-gas transmitting light or integrating the two-group detected values for the same hour. CONSTITUTION:The detected value of a transmission light source light detection system of a cell 21 in which zero gas is flowed through a gain control circuit 27 and a detector 23 etc. and the detected value of a light source light detection system by a detector 24, are impressed to a differential amplifier 28 and gains of the circuit 27 are controlled and fixed with the amplifier 28 in accordance with the accuracy of the amplifier 28. Further, each output of the amplifier 28 and the light source light detection system is integrated for the same hour by integrators 29, 32 which are controlled by an operation processing circuit 35 and the integration ratio is stored in the circuit 35. Next, the integration ratio is calculated by flowing a sample gas into the cell 21 fixing the gains of the circuit 27 as it is, and the difference between the stored integration ratio proportional to the concentration of gaseous component and said ratio is calculated by the circuit 35. Hereby, a simple constitution which is eliminated the need of highly accurate parts in the integrator or the operation circuit is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an absorption type analyzer that measures the concentration of a component to be measured using an absorption method, and is particularly suitable for measuring extremely low concentration components such as ozone contained in the atmosphere. Regarding the meter.

When measuring the ozone concentration in the atmosphere using absorption method,
For example, 0. In IPPM ozone, the amount of transmitted light is 0.
While the light absorbs only about 1%, the light source absorbs only 0.1%.
It moves about f. For this reason, it is impossible to measure ozone concentration using normal absorption methods.

Japanese Patent Laid-Open No. 51-2917 has been developed as a method to eliminate such fluctuations in the light source and make it possible to measure ozone concentration.
There is a measurement circuit described in Publication No. 6. In principle, this circuit consists of a detector 2 that detects the light that has passed through the measurement cell 1, a detector 4 that directly detects the light from the light source 3, and each of the detectors 2 and 4 as shown in Figure 4fj1. A V-F converter 5.6 that performs V-F conversion of the detection signal, and an up/down counter 7 that counts the pulse signals output from each conversion 65, 6.
It consists of ゜8. How to use this circuit is to first fill the measuring cell 1 with zero gas prior to measurement.

In this state, pulse signals obtained from each of the detectors 2 and 4 via the V-F converters 5 and 6 are counted up.

When the count value of the up-down counter 7 (line 7' in FIG. 2, 8' indicates the count value of the up-down counter 8) reaches a certain value, for example K, both counters 7. Stop the count of 8.

Next, a measurement gas is put into the measurement cell 1, and the pulse signals emitted from the V-Ff converters 5 and 6 in this state are applied to the up/down counter 7.8 to count down from the previous count value. Then, when the count value of the up/down counter 8 becomes zero, the counting of both counters 7.8 is stopped. The count value V (see FIG. 2) of the up/down counter 7 at the time of this counting stop becomes output data. In this case, the cell length of measurement cell l is set to 1
If 1 gas concentration is x1 and the absorption coefficient is C, then the count value V becomes v=Kclx.

In this conventional means, as described above, the amount of light is integrated until it reaches a constant value, so the influence of light source modification is eliminated. Therefore, it is possible to accurately measure low concentration components such as ozone.

However, in order to make it actually possible to measure low-concentration components using this conventional means, it is necessary that both of the two V-F converters have an accuracy of the order corresponding to the concentration, and that the two The down counter must also be able to count up to the order of magnitude, which has the disadvantage that the device is very expensive. For example, I
In order to measure PPM ozone with an accuracy of 0.1%, the amount of light from the light source must be measured with an accuracy of lo-6,
Naturally, the V-F converter is required to have an accuracy on the order of lo-6, and the up/down counter is required to be capable of counting as many as 6 digits.

In addition, this conventional method uses a method of integrating the measurement signal until the integrated value of the light amount reaches a certain value, and can be used to measure continuous signals where both the reference side and the measurement side continuously receive instructions. However, it has the disadvantage that it cannot be used when the peak value is indicated only on the measurement side. This is because with conventional means, fluctuations in the amount of light occur in both the measurement signal and the signal from the detector that detects the direct light from the light source, and as a result, the effects of fluctuations in the light source can be canceled out. .

However, in many cases, such as when burning and gasifying a solid sample and analyzing it with an absorption spectrometer, it is necessary to measure signals that appear as short-period, single-shot pulses, and batch measurements also require 0T capability. The need for this is high.

In view of these points, the present invention allows the use of inexpensive equipment such as an integrator that does not have very high accuracy or the number of display digits, and yet allows the measurement of components to be measured such as ozone concentration without being affected by fluctuations in the light source. The present invention provides an excellent absorption spectrometer that can be used for batch measurements.

Accordingly, the present invention includes a light source, two photodetectors, and at least one cell disposed in the optical path from the light source to the photodetector, and a sample for comparison or measurement is placed in the cell. A signal detected by a first photodetector in an absorption spectrometer that analyzes a component to be measured through a first step of flowing one of the samples and a second step of flowing the other sample into the cell. a gain control circuit that controls the gain of the control circuit; a differential amplifier that amplifies the difference between the gain-controlled signal that controls the control circuit by 1ffl; and the signal detected by the second photodetector; a first integrator that integrates the output signal of the dynamic amplifier, a second integrator that integrates the signal of the second photodetector, and an arithmetic processing circuit that performs arithmetic processing on the outputs of these integrator; In the first step, the gain of the gain control path 1.01 is adjusted so that the signal from the first photodetector and the signal from the second photodetector are equal with a predetermined accuracy. , is identified, with the fixed gain, the first integrator integrates the signal emitted from the differential amplifier for a certain period of time, and at the same time as this integration, the second integrator also performs integration for the same period of time. In the second step, with the gain of the gain control circuit fixed at the gain adjusted in the first step, the signal emitted from the differential amplifier is used in the first integrator, and the signal from the photodetector in Collection 2 is sent to the first integrator. 2
The arithmetic processing circuit calculates the ratio of the integrated values of the two integrators in the first step and the integrated value of the two integrators in the second step. The gist is to find the difference between the ratio and the ratio. Here, the modes in which cells are placed in the optical path from the light source to the detector include the single cell method in which the cells are placed only in the optical path from the light source to one detector, and the two optical paths from the light source to two detectors. There is a double cell method in which separate cells are placed inside each cell. In the case of a single cell system, the cell can be placed in either the optical path from the light source to the first detector or the optical path to the second detector. And in case of single cell system, @1
In the step, zero gas is flowed through the cell, and in the second step, sample gas is flowed through the cell. On the other hand, in the case of a double cell method, one cell is constantly supplied with zero gas, the other is supplied with zero gas in the first step, and the sample gas is supplied with the second step; Flow the zero gas into the other cell and the sample gas into the other cell.
In the second step, there are two methods: switching the gas flow to flow the sample gas into one cell and the zero gas into the other cell.
Two methods can be used. Further, as the zero gas used in these double cell systems, it is desirable to use a gas obtained by adding the sample gas to a zero gas purifier to remove only the components to be measured (interfering components remain as they are). The present invention can be implemented using any of these cell arrangement methods.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

Figure 4fJ3 shows an example in which the present invention is applied to a single cell system in which one cell 21 is placed between a light source 22 and a first photodetector 23, and 24 in the figure is a second photodetector. , 25
．． 26 is a preamplifier, 27 is a gain control circuit,
28 is a differential amplifier, 29 is a first integrator for integrating the output signal of the differential amplifier 2B, and is composed of a V-F converter 30 and a counter 31. 32 is a @2 integrator that integrates the signal of the second photodetector 24, which is the same as the first integrator (consisting of a V-F converter 33 and a counter 34; 35 is a This is an arithmetic processing circuit that performs arithmetic processing on the outputs of the arithmetic units 29 and 32. This circuit 35 is configured with a microcomputer, etc., so that in addition to the above arithmetic processing, it also performs count start, stop control, and reset of each counter 31.34. Counting start and stop are performed at the same time for each counter 31 and 34, and the time from counting start to stop is set to a fixed time.This time can be determined by operating the arithmetic processing circuit 35. 36 is a sample hold circuit that holds the output of the arithmetic processing circuit 35.

In the above configuration, the first step is performed as follows.

First, zero gas is flowed into the cell 21. At this time, the difference between the signal 0 obtained from the first detector 23 through the gain control circuit @27 and the signal JO obtained from the second detector z4 through the preamplifier 26 is amplified by the differential amplifier 28, Both signals Io.

The gain of the gain control circuit 27 is adjusted by the output signal of the differential amplifier 28 so that the JoO values are equal to a predetermined accuracy, and is fixed at that gain. Here, as the predetermined accuracy, if measurement is to be performed with an accuracy on the order of 10-6, for example, an accuracy on the order of lo-3 is appropriate.

If the gain of the gain control circuit 27 is adjusted in this order, both signals 1o and Jo will match up to the order of 10-3. However, the two signals cannot be said to match in the range of orders higher than that, that is, orders of 10-4 to 10-6. Therefore, the output of the differential amplifier 28 is the difference between the two signals Io and Jo. ,
A range of unmatched signals of the order of till-' to 10-6 is obtained. However, differential amplifier 2
The amplification rate of 8 is usually higher than 1000 times, so
Both signals 1o.

The signal value of the difference between Jo is amplified to the same magnitude as the original signals Io and Jo.

Once the gain of the gain control circuit 27 is fixed, the arithmetic processing circuit 35 issues a start signal to start the counters 31 and 34 of the two integrator 29 and 32 simultaneously. The counter 31 counts the output signal of the differential amplifier 28, and the counter 34 counts the signal of the second photodetector 24. When a certain period of time has elapsed from the start of counting, a stop signal is issued from the arithmetic processing circuit 35, and both counters 31 and 34 stop counting.

The count values of both counters at this time are output to the arithmetic processing circuit. Letting the output of the counter 31 be 7 and the output of the counter 34 be D21, the arithmetic processing circuit 35 calculates the ratio D11/T)2 of both count values. Find the value and memorize it. This completes the first step. After completing this process, 142
The counters 31 and 34 are reset before the start of the process.

In step $2, sample gas is flowed into the cell 21 instead of zero gas. The light passing through this sample gas is $1
The signal is detected by the detector 23, and is applied to the differential amplifier 28 through the gain control circuit 27 whose gain is adjusted and fixed in the fourth step.

The differential amplifier 28 receives a signal I that directly detects the light from the light source 22.
Since /O is added, the difference signal between this signal JO/ and the signal 11 that has passed through the gain control circuit 27 is amplified and sent to the output of the differential amplifier 28. The counter 31 is connected to the differential amplifier 28 by the start signal.
As in the first step, the counter 31 is started and stopped simultaneously with the other counter 34, and the counting time is also set to be the same as the time in the first step. Thus, when both counters 31 and 34 stop counting, the count values at that time are input to the arithmetic processing circuit 35.

When the count value of the counter 31 is Dit and the count value of the counter 34 is Do, the arithmetic processing circuit 35 calculates the ratio Dv / D22 of both count values, and calculates this ratio from the ratio Do / Dzt calculated at the end of the first step. Subtract.

The subtracted value is c;, = D++ / D, , " / Dtz, and this value is held in the sample and hold circuit 36 and output as output data. This output data is the value of the component to be measured. The reason why the output data indicates the concentration of the component to be measured becomes clear if you compare it with the absorption spectrometer that uses the integrated value fixed method mentioned at the beginning.In other words, the integrated value fixed method uses the second light detection The first photodetector detects and integrates the transmitted light of the measurement cell until the integrated value of the amount of light source light detected by the device reaches a certain value, and this results in the integration of the transmitted light of the measurement cell. This method performs division by dividing the value by the integrated value of the amount of light from the light source.Therefore, the configuration of the present invention for determining the ratio Du/D21.DI27Dn is also basically equivalent to the conventional means.

Therefore, by calculating D1〆'Do D+V/D22, the concentration of the component to be measured can be determined. However, the configuration of the present invention does not use a method of fixing the integrated value, but uses a method of fixing the integrated time to a constant time, so unlike conventional means, it can also be used for batch measurements. Figure 4 shows the counter 3 in the first and second steps.
1.34 and the operation of the arithmetic processing circuit.

Additionally, in the configuration of the present invention, the signals on the first detector side and the second detector side are predetermined (on the order of 1o-').
The gain control circuit 2 is adjusted to match the accuracy of
7 is adjusted and the gain is fixed during the 11th and 2nd steps (this period is referred to as 1 cycle), so the V-F converter 3Q that constitutes the integrator 29
The counter 31 cannot be set to -1 by the gain control circuit 27, or there is no guarantee that they will match. : It is enough if you can guarantee that the tweet will be converted to V-F and counted.
Therefore, the accuracy of the V-F converter is sufficient as the accuracy obtained by dividing the accuracy (io') required for measurement by the accuracy (lo') of the gain control circuit 27, and the number of digits of the counter 31 is The number of digits (3 digits) equal to the exponent value of precision required for 3o is sufficient.

Therefore, compared to conventional means, it can be constructed at a lower cost using easily available parts.

As mentioned above, the present invention is applicable not only to the single cell system but also to the system using the light source 22 and the two detectors 23 .
It can also be applied to a double cell system in which the cells 21 and 32 are provided in two optical paths leading to the cell 24. In this case, cell 3
Zero gas may be allowed to flow through cell 21 in the first step and sample gas may be allowed to flow in the second step. At this time, it is desirable to use a zero gas obtained by passing the sample gas through a zero gas purification product and containing interference components. In this double cell system as well as in the single cell system, the D
By calculating o/D21-DI2/D2□, the concentration of the component to be measured can be measured. Particularly, this method has the advantage that the influence of the interfering component gas is canceled out, so that the influence of the interfering component gas is not affected by the output.

In addition, in a double cell configuration similar to the above, 'fJ1
In the process, the sample gas is transferred to the cell 21 on the side “−” and the sample gas is transferred to the cell 3 on the other side.
The present invention can also be applied to a so-called cross-flow method in which zero gas is supplied to one cell 21 and sample gas is supplied to the other cell 32 in the second step.

In this case, the characteristic of the crossflow one-sided method is exhibited, that is, the output is doubled, and the measurement becomes more accurate at 1'TE.

Although a more detailed explanation will be omitted, even if the cell 21 is provided between the light source α 22 and the second detector 24 in the single cell system, contrary to the configuration shown in FIG. 3, the configuration shown in FIG. Almost similar measurements are possible.

Since the absorption spectrometer according to the present invention is constructed as described above, it has the following effects.

■ Since the gain control circuit adjusts and fixes the vJl detector side and second detector side signals equally to a predetermined precision, it is possible to measure low concentration components with high precision, but the first integration It is possible to use a low-precision device that is generally easily available. Furthermore, for the same reason, a relatively low-precision arithmetic processing circuit can be used. Therefore, the entire device can be constructed at low cost.

(11) Since it adopts a fixed integration time method in which the second integrator integrates for a certain period of time, it can also be used for batch measurements, making it possible to analyze a wide range of measurement targets.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a conventional absorption analyzer, FIG. 2 is a diagram explaining the measurement operation of the circuit in FIG. 1, and FIG. 3 is an overall circuit diagram showing an embodiment of the present invention. FIG. 4 is a diagram explaining the measurement operation of the circuit of FIG. 3, and FIG. 5 is a diagram showing a cell system to which the present invention can be applied. 21.32...Cell, 22...Light source, 23...First detector, 24...Second detector, 27...Gain control circuit, 28...Differential gain 1 interval Vessel, 29...
First integrator, 32... second integrator, 35... arithmetic processing circuit.

Claims (1)

[Scope of Claims] It has a light source, two photodetectors, and at least one cell disposed in the optical path from the light source to the photodetector, and the cell includes a sample for comparison or measurement. In an absorption spectrometer that analyzes a component to be measured through a first step of flowing one sample and a second step of flowing the other sample through the cell, the signal detected by the first photodetector is a gain control circuit for controlling gain; a differential amplifier for amplifying the difference between the gain-controlled signal passing through the control circuit and the signal detected by the second photodetector; and the differential amplifier. a second integrator that integrates the signals of the photodetector @2, and an arithmetic processing circuit that performs arithmetic processing on the outputs of these integrator; In step 1, after adjusting and fixing the gain of the gain control circuit so that the signal from the first photodetector and the signal from the second photodetector are equal with a predetermined accuracy, With the fixed gain, the first integrator integrates the signal emitted from the differential amplifier for a certain period of time, and at the same time, the second integrator is also integrated, and in the second step, With the gain of the gain control circuit fixed at the gain adjusted in the first step, the signal emitted from the differential amplifier is sent to the first integrator, and the signal from the photodetector in Collection 2 is sent to the second integrator. The arithmetic processing circuit calculates the ratio of the integrated values of the two integrators in the first step and the ratio of the integrated values of the two integrators in the second step. An absorption spectrometer characterized by determining the difference.