JPH0242338A - Gas analyzer - Google Patents

Abstract

PURPOSE:To securely and accurately compensate all of a span drift at all times by performing the synchronous detection and rectification and smoothing processing of the output signal of an absorbance detector with a synchronizing signal representing optical modulating operation. CONSTITUTION:The synchronous detection and rectification and smoothing processing of the output signal of the absorbance detector 3 are carried out with a synchronizing signal representing gas modulating operation and the synchronizing signal representing the optical modulating operation. Consequently, a 1st rectified signal ¦V1¦ regarding the gas modulation and a 2nd rectified signal ¦V2¦ regarding the optical modulation are extracted individually and the signal ¦V1¦ is divided by the signal ¦V2¦. Then the influence of various factors of the variation quantity of an AC component regarding the gas modulation to be measured directly is canceled and removed securely and effectively only by adding a structure for varying the intensity of the irradiating light from a light source and providing a correcting means X by mere internal signal processing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is a method for measuring components to be measured (for example, NO) in a sample gas.
−? ) A gas analyzer used to measure the concentration (and thus the amount) of Go, etc.), in particular a light source for a measurement cell into which a reference gas and a sample gas are alternately introduced at a predetermined gas modulation frequency. and an absorbance detector for the light that has passed through the reference gas and the light that has passed through the summable gas, and detects the reference gas from the output signal from the absorbance detector. It is configured to extract an alternating current component corresponding to the energy difference between the light energy that has passed and the light energy that has passed through the sample gas, and to measure the concentration of the component to be measured in the sample gas based on the amount of change in the alternating current component. Regarding the gas analyzer.

[Conventional technology]

As a pioneer and representative gas analyzer of this type,
For example, Japanese Patent Publication No. 56-4882 proposed by the applicant
As is known from Publication No. 2 (in this case, a cross-flow type is adopted), the reference gas (usually zero gas is used) and the sample gas are connected at a constant period (
(Basic frequency of the AC component described below as measurement data)
For example, a pneumatic ink type detector (
(condenser microphone detector, etc.), the AC component corresponding to the energy difference between the light energy that has passed through the reference gas and the light energy that has passed through the sample gas (the amount of light absorption energy by the component to be measured in the sample gas) is There is a type of gas analyzer that uses a so-called light intensity difference detector, which allows direct current to be extracted in a form that does not contain DC components, but recently there are also gas analyzers that use a measuring cell, such as a thermopile detector. A light intensity detector that detects changes in the absolute value of the light energy that has passed through it (the output signal from this is a direct current component that corresponds to a constant light energy that has passed through the reference gas, and a direct current component that corresponds to the amount of light absorption energy by the component to be measured in the sample gas) There is also known a type of gas analyzer that uses a superimposed alternating current component, and is configured to extract an alternating current component corresponding to the amount of absorbed energy through signal processing.

[Problem to be solved by the invention]

By the way, in this type of gas analyzer, the former type uses a light intensity difference detector such as a nematic type detector,
Either the structure directly extracts the alternating current component corresponding to the amount of light absorption energy, or the latter type (using a light amount detector that detects the absolute value of light energy such as a thermopile detector, and signal processing). In any case, changes in the amount of light due to changes in the voltage applied to the light source, changes in ambient temperature, deterioration of the light source itself, and transmission through the gas distribution cell. Span drift inevitably occurs due to factors such as dirty windows and changes in the sensitivity of the absorbance detector itself.

Therefore, in order to prevent the occurrence of such span drift as much as possible, conventional measures have been taken such as providing a means to stabilize the voltage applied to the light source and a means to maintain the ambient temperature constant at all times. However, in that case, not only does the entire device become extremely large and complicated, but it also causes deterioration of the light source itself, dirt on the transmission window of the gas flow cell, and damage to the absorbance detector itself. Since span drift due to changes in the characteristics of the optical system due to factors such as sensitivity changes over time cannot be compensated for, calibration operations using standard span gas must be performed frequently, which is extremely troublesome and consumes a large amount of span gas. There was a problem in that it was extremely uneconomical because a large amount was required. In particular, when measuring gases for which it is difficult to supply a stable span gas,
Its shortcomings are very noticeable.

Therefore, the present inventors have developed a technology capable of solving the above-mentioned problems regarding the latter type of gas analyzer mentioned above, and this is disclosed in Japanese Patent Application No. 61-222326 (September 20, 1986). This has already been proposed by the Japanese Patent Application (Japanese).

In addition to the AC component, which corresponds to the amount of light absorption energy by the component to be measured in the sample gas, from the output signal from the light intensity detector, a DC component, which corresponds to a constant light energy that has passed through the reference gas, is also extracted. By providing a correction means that divides the amount of change in the AC component by the component, or a correction means equivalent thereto, the components that are commonly and equally included in the AC component and the DC component (in the same proportion) The influence of the characteristics of the optical system, such as the light intensity of the light source, the light transmittance of the transmission window of the gas distribution cell, and the sensitivity of the light intensity detector, is canceled out by the division function of the correction means, and the alternating current component that is the direct measurement target is The structure is such that the influence of the various factors mentioned above on the amount of change in can be reliably and effectively removed.

However, the technology related to the above-mentioned patent application is based on the latter type of gas analyzer (DC component corresponding to constant light energy passing through the reference gas and AC component corresponding to the amount of light absorption energy by the component to be measured in the sample gas). It can be effectively applied to gas analyzers of the former type (those using light intensity detectors such as thermopile detectors that output signals equivalent to absolute values in a superimposed form); It cannot be applied to gas analyzers of the former type (using a light intensity difference detector such as a pneumatic ink detector that outputs a signal consisting only of alternating current components corresponding to the amount of The aforementioned problems have not yet been resolved.

The present invention was made in view of such circumstances, and
The purpose of this is to eliminate the need for large-scale measures to stabilize the voltage applied to the light source or to maintain constant ambient temperature, as in the past, and to eliminate the need for uneconomical and troublesome calibration procedures using standard span gas. It is possible to effectively compensate for all the span drifts caused by the various factors described above by simply adding an internal signal processing means and an extremely simple and inexpensive structure without having to perform The purpose of this research is to develop and provide span drift compensation technology that can be applied to any type of gas analyzer.

[Means to solve the problem]

In order to achieve the above object, the gas analyzer according to the present invention has the basic configuration as described at the beginning, and the intensity of the irradiated light from the light source is optically modulated at the same frequency as the gas modulation frequency. synchronously detecting and rectifying the output signal from the absorbance detector with a synchronous signal representing the gas modulating operation; and smoothing to obtain a first rectified signal regarding the gas modulation, and to the output signal from the absorbance detector,
The configuration is configured to obtain a second rectified signal regarding the optical modulation by performing synchronous detection rectification and smoothing processing using a synchronization signal representing the optical modulation operation, and convert the first rectified signal into a second rectified signal.
It is characterized in that it is provided with a signal processing circuit having a correction means for dividing by a rectified signal or an equivalent correction means.

[Effect]

The effects achieved due to this characteristic configuration are as follows.

That is, according to the gas analysis needle according to the present invention, as will be explained in detail in the description of the embodiments described later, the output signal from the absorbance detector is an AC signal related to gas modulation, which is the original measurement data. (AC component corresponding to the amount of absorption energy by the component to be measured in the sample gas), intentionally generates an AC signal related to optical modulation (AC component based on the intensity change of the irradiated light from the light source) with a different phase relationship. The structure is configured so that a signal in the form of a superimposed signal can be extracted, and both the AC component related to the gas modulation and the AC component related to the light modulation are controlled by the light intensity of the light source, the light transmittance of the transparent core of the gas distribution cell, Based on the results of consideration that the effects of the characteristics of the optical system such as the sensitivity of the absorbance detector are equally involved (in the same proportion), a synchronization signal representing the gas modulation operation is determined from the output signal of the absorbance detector. The first rectified signal related to the gas modulation and the second rectified signal related to the optical modulation are separately extracted by performing synchronous detection rectification and smoothing processing on the synchronous signal representing the optical modulation operation, and the synchronous signal representing the optical modulation operation, respectively. By configuring the first rectification signal to be divided by the second rectification signal, the influence of the various factors on the amount of change in the alternating current component related to the gas modulation, which is the direct measurement target, can be reduced by the influence of the irradiation light from the light source. By simply adding an extremely simple and inexpensive structure to change the intensity and a correction means based on simple internal signal processing, it is now possible to reliably and effectively cancel out and remove it.
Therefore, unlike conventional methods, there is no need to provide large-scale means to stabilize the voltage applied to the light source, to maintain constant ambient temperature, or to provide other special compensation detectors, making it extremely simple. It is compact and can be constructed at low cost, and it also eliminates the need to perform uneconomical and troublesome calibration operations using a standard span gas as often as in the past, and is capable of handling changes in the applied voltage to the light source, changes in ambient temperature, and the light source. It is now possible to always reliably and accurately compensate for span drift caused by various factors such as changes in light intensity due to deterioration of the detector itself, dirt on the transmission window of the gas flow cell, and changes in the sensitivity of the detector itself. Ta.

Moreover, in the present invention, as described above, the output signal from the absorbance detector is an AC signal related to gas modulation, which is the original measurement data (AC component corresponding to the amount of light absorption energy by the component to be measured in the sample gas). In contrast, we adopted a method of configuring the system to extract a signal in the form of intentionally superimposing AC signals related to optical modulation (AC components based on changes in the intensity of the irradiated light from the light source) that have a different phase relationship. Therefore, the present invention is particularly applicable to a type of light intensity difference detector such as a pneumatic ink type detector that outputs a signal consisting only of an alternating current component corresponding to the amount of absorption energy by a component to be measured in a sample gas. Not only can it be suitably used for gas analyzers, but it can also be used in a form in which an alternating current component corresponding to the amount of light energy absorbed by the component to be measured in the sample gas is superimposed on a direct current component corresponding to a constant light energy that has passed through the reference gas. It is also fully applicable to a type of gas analyzer that uses a light intensity detector such as a thermopile detector that outputs a signal equivalent to an absolute value.

〔Example〕

Hereinafter, various specific embodiments of the present invention will be described based on the drawings.

1 to 3 show a single cell type cross-flow gas analyzer according to a basic embodiment of the present invention.

In the overall schematic configuration diagram of FIG. 1, A is an absorbance detection section for detecting the absorbance due to the measurement target component gas contained in the sample gas, and B is an operating voltage applied to the light source l in the absorbance detection section A. C is a power supply circuit for supplying, for example, a three-way switching valve or It is a gas distributor composed of a four-way switching valve, a rotary valve, etc., and D is the absorbance detection section A.
is a signal processing circuit for the output signal from the absorbance detector 3, E is a display that displays a value (gas concentration as a measurement result) corresponding to the output signal from the signal processing circuit, and F is a signal processing circuit for the output signal from the absorbance detector 3; For the power supply circuit B and the gas distributor C1 signal processing circuit, as shown by thin solid line arrows in the figure, the valve switching signal, the corresponding gas switching signal, and the optical modulation signal (in this example, all This is a controller that emits a predetermined control signal such as (set to IHz).

That is, the absorbance detection section A uses a light source 1 for irradiating measurement light (for example, infrared rays) and a gas distributor B to adjust the sample gas and reference gas to a predetermined gas modulation frequency (IHz).
), the reference gas is introduced into the measurement cell 2 (absorption of light energy does not occur), and the sample gas is introduced (
The absorbance detector 3 consists of a light intensity difference detector (for example, a pneumatic ink type detector such as a condenser microphone detector) for detecting the light energy difference between the They are arranged in that order so that a linear relationship is established.

In addition, the power supply circuit B applies the voltage from the constant voltage power supply 4 and the constant voltage power supply 1 for the light source to a light modulation frequency (the same frequency as the gas modulation frequency) based on the light modulation signal from the controller F. IHz) and with a phase relationship different from that of the gas modulation operation (in this example, the phase difference θ is set to 90'' or approximately 90'').
It is comprised of a voltage modulation circuit 5 (which changes the strength or strength).

The signal processing circuit is constructed as shown in the block circuit diagram of FIG. Hereinafter, the configuration of this signal processing circuit will be explained in detail with reference to the explanatory diagram of input signals shown in FIG. 3(a) and the timing chart of each part signal shown in FIG. 3(b).

First, to explain in advance the detection signal V input from the absorbance detector 3 to this signal processing circuit, this detection signal V is, as shown in FIG. AC component Vl of IH2 regarding gas modulation of
(The AC component corresponding to the amount of light absorption energy by the component to be measured in the sample gas has a phase relationship of θ (=9
0@) AC component V2 (AC component based on the intensity change of the irradiated light from the light source 1) of different frequencies IHz are superimposed. In addition, both the AC component vl related to gas modulation and the AC component v2 related to light modulation,
It is clear that the effects of the characteristics of the optical system, such as the amount of light a11, the light transmittance of the transmission window of the gas flow cell 2, and the sensitivity of the absorbance detector 3, are equally involved (in the same proportion). As will become clear from the description below, this is a very important point for the present invention.

The signal processing circuit shown in FIG. 2 amplifies the detection signal V supplied via the input terminal a, and
As shown in Figure (B), there is an AC component vl' (amplified from the AC component v1) related to the gas modulation that corresponds to the original measurement data, and an AC component v2'' (the AC component v2) related to the optical modulation, which has a different phase relationship from it. amplified component v2)
The signal V (=vl' +V2
a preamplifier 6 for extracting the signal V) and a bandpass filter 7 (with a center frequency of
By synchronously rectifying the output signal of the band-pass filter 7 based on the gas switching signal (lHz) supplied from the controller F via the input terminal S, the AC component v1° related to the gas modulation is A first synchronous detection rectifier circuit 8A for extracting only the signal 1 (in other words, the values after smoothing are equal to each other), and a first synchronous detection rectifier circuit 8A that smoothes the output signal from the first synchronous detection rectifier circuit 8A. A smoothing circuit 9A (for example, a low-pass filter) for obtaining the rectified signal IVII and an optical switching signal (IHz,
θ=90°), the bandpass filter 7
By synchronously rectifying the output signal of
A synchronous detection rectifier circuit 8B and a second rectified signal 1v2 obtained by smoothing the output signal from the second synchronous detection rectifier circuit 8B.
1 and the first smoothing circuit 9A.
and a divider 10 for dividing the first rectified signal IVII inputted from the second smoothing circuit 9B by the second rectified signal 121 inputted from the second smoothing circuit 9B. The output signal v3 is supplied to the output terminal d of the display E, and is displayed as a concentration value of the component to be measured contained in the sample gas.

Then, by the process of dividing the first rectified signal Vll corresponding to the original measurement data by the second rectified signal IV21 corresponding to the intensity change of the irradiated light, which is performed by the divider 10, each rectified signal is Since the effects of the various factors on the characteristics of the optical system described above, which are equally included (in the same proportion), are canceled out, the output signal from the divider 10 (final concentration measurement signal) is
Its influence is reliably and effectively removed. Therefore, for example, changes in the amount of light due to changes in the voltage applied to the light source 1 or changes in ambient temperature, deterioration of the light source 1 itself, etc.
Changes in transmittance due to dirt on the transmission window of the absorbance detector 3
Even if various changes occur over time, such as changes in the sensitivity of the signal itself, the effects (span drift) caused by these changes will affect the output signal (3) from the divider 10 of the signal processing circuit to the indicator E. is not included, so that the indicator E always indicates a value that accurately corresponds to the concentration of the sample gas.

Therefore, herein, the bandpass filter 7, both synchronous detection rectifier circuits 8A, 8B, both smoothing circuits 9A, 9B, divider 10, etc. are collectively referred to as correction means X.

FIG. 4 shows another embodiment in which, instead of using electrical means such as the voltage modulation circuit 5 in the basic embodiment as a means for changing the intensity of the irradiated light from the light source l, As shown in FIG. 4(a), the power supply circuit B
is a mechanical means that consists only of a constant voltage power supply 4 for the light source and emits light of a constant intensity from the light source 1, while providing a chopper device 14 for partially chopping the emitted light at the above-mentioned frequency. It uses This chopper device 14 is composed of a drive motor 12 and a blade body 13 that is rotationally driven by the drive motor 12. As shown in the enlarged front view of FIG. During half a rotation, all of the irradiated light from the light St passes through, making the light supplied to the gas distribution cell 2 in a strong luminosity state, but during the other half rotation, part of the irradiated light is passed through. It is formed in a blade shape so that the light supplied to the gas circulation cell 2 is brought into a low luminosity state by blocking the light. In the case of this chopper device 14, in order to perform optical modulation at IHz as in the case of the previous embodiment, the motor 12 may be rotated at IHz.

However, the rotation speed of this motor 12 is determined by the target frequency of optical modulation and the shape of the blade body 13, and if the blade body 13 is made into another shape (for example, a two-blade type), the motor 12 can be / 2 Hz. The other configurations in this embodiment are the same as those in the basic embodiment, so members having the same functions are designated by the same reference numerals.
The explanation will be omitted.

FIG. 5 shows a modification of the signal processing circuit shown in FIG.
The first rectified signal 1v11 directly obtained by
The first rectified signal 1v21 obtained directly by the synchronous detection rectification circuit 8B and the second smoothing circuit 9B is not configured to be directly divided using the divider 10, but by the preamplifier 6 and the bandpass filter. An auto gain controller (hereinafter referred to as AGC) 15 is interposed between the ACCI 2 and the second smoothing circuit 9B, and a comparator 16 with a reference voltage of V is interposed between the ACCI 2 and the second smoothing circuit 9B.
By configuring the correction means X that performs feedback control on the AGC 12 so that the second rectified signal 121 obtained by the second synchronous detection rectification circuit 8B and the second smoothing circuit 9B is always maintained at a constant value V. , an operation (indirect division) equivalent to that of the basic embodiment described above is performed.

By the way, the configuration of the signal processing circuit in each of the above-described embodiments is of a pneumatic type that outputs a signal consisting only of an alternating current component corresponding to the absorption energy I by the component to be measured in the sample gas as the absorbance detector 3. It is configured to correspond to the case where a light intensity difference detector such as a detector is used, but it has a direct current component equivalent to the constant light energy that passed through the reference gas, and a direct current component equivalent to the amount of light absorption energy by the component to be measured in the sample gas. When using a light intensity detector such as a thermopile detector that outputs a signal equivalent to an absolute value in the form of a superimposed AC component, an AC amplifier circuit 17 is installed immediately after the preamplifier 6, as shown in FIG. It is only necessary to remove the direct current component by interposing the DC component, and then perform the same signal processing as described above. Therefore, the present invention is fully applicable to a gas analyzer using such a light amount detector. It is.

FIG. 7 also shows two sets of lights s1. 1 and gas distribution cells 2, 2 are provided, and both gas distribution cells 2 are controlled by a gas distributor C1C consisting of two switching valves.
．． An embodiment in which the present invention is applied to a so-called double cell type cross-flow gas analyzer configured to alternately and reciprocally introduce a sample gas and a reference gas into a gas analyzer. It shows. Note that the other configurations in this embodiment are the same as those in the basic embodiment described above, so members having the same functions are designated by the same reference numerals, and the explanation thereof will be omitted.

〔Effect of the invention〕

As is clear from the detailed description above, according to the gas analyzer according to the present invention, an AC signal related to gas modulation, which is the original measurement data (AC component corresponding to the amount of light absorption energy by the measurement target component in the sample gas) ), it is configured to extract a signal in the form of intentionally superimposing an AC signal related to optical modulation (AC component based on the intensity change of the irradiated light from the light source) with a different phase relationship from that, and the gas Both the alternating current component related to modulation and the alternating current component related to optical modulation are equally affected by optical system characteristics such as the light intensity of the light source, the optical i3 pass rate of the transmission window of the gas flow cell, and the sensitivity of the absorbance detector. (in the same proportion), from the output signal from the absorbance detector, the synchronization signal representing the gas modulation operation and the synchronization signal representing the light modulation operation are used to perform synchronous detection rectification and rectification, respectively. The first rectified signal related to the gas modulation and the second rectified signal related to the optical modulation are respectively extracted by smoothing processing, and the first rectified signal is divided by the second rectified signal. In this way, the effect of the various factors on the amount of change in the alternating current component related to the gas modulation, which is the object of direct measurement, can be reduced by adding a simple and inexpensive structure to change the intensity of the irradiated light from the light source. By simply applying a correction means based on internal signal processing, it is now possible to reliably and effectively cancel and remove the voltage. It is an extremely simple, compact, and inexpensive structure that does not require the installation of large-scale means to constantly maintain a constant state or any other special compensation detector, and yet it can be constructed as standard as before. There is no need to frequently perform uneconomical and troublesome calibration operations using span gas, and there is no need to perform frequent calibration operations that are uneconomical and troublesome. It is now possible to always reliably and accurately compensate for all span drifts caused by various factors such as changes in the sensitivity of the instrument itself.
Furthermore, as described above, as an output signal from the absorbance detector, an AC signal related to gas modulation (an AC component corresponding to the absorption energy I by the component to be measured in the sample gas), which is the original measurement data, is is configured to be able to extract a signal in the form of intentionally superimposing AC signals related to optical modulation (AC components based on intensity changes of the irradiated light from the light source) having different phase relationships. The present invention can be suitably used in a gas analyzer using a light intensity difference detector such as a pneumatic ink detector that outputs a signal consisting only of an alternating current component corresponding to the amount of absorption energy by the component to be measured in the gas. Of course, the thermodetector outputs a signal corresponding to the absolute value in the form of a DC component corresponding to the constant light energy passing through the reference gas and an AC component corresponding to the amount of light absorption energy by the component to be measured in the sample gas superimposed. It can be fully applied to gas analyzers using light intensity detectors such as
This excellent effect has been achieved.

[Brief explanation of the drawing]

The drawings show various specific embodiments of the gas analyzer according to the present invention, FIG. 1 is a general schematic diagram of the basic embodiment, FIG. 2 is a block circuit diagram of the signal processing circuit, and FIG. (A) is an explanatory diagram of the output signal of the absorbance detector, FIG. 3 (B) is a signal diagram of each possible part in the signal processing circuit, and FIG.
Figure (a) is an overall schematic configuration diagram of another embodiment, and Figure 4 (b)
is an enlarged front view of the main parts thereof, FIG. 5 is a block circuit configuration diagram of a modified example of the signal processing circuit, FIG. 6 is a main part circuit diagram of another modified example of the signal processing circuit, and FIG. FIG. 7 is an overall schematic diagram of another embodiment. Z...Reference gas, S...Sample gas, l...Light source, 2...
...Measurement cell, 3...Absorbance detector, θ・
...Phase difference, X...Correction means. Applicant Horiba Manufacturing Co., Ltd. Representative Patent Attorney Hideo Imoto

Claims (1)

[Scope of Claims] The measurement cell is configured to allow light emitted from a light source to pass through a measurement cell into which a reference gas and a sample gas are alternately introduced at a predetermined gas modulation frequency, and the reference gas is An absorbance detector is provided for the light that has passed through the sample gas and the light that has passed through the sample gas, and the output signal from the absorbance detector is determined based on the energy difference between the light energy that has passed through the reference gas and the light energy that has passed through the sample gas. In a gas analyzer configured to extract a corresponding alternating current component and measure the concentration of a component to be measured in the sample gas based on the amount of change in the alternating current component, the intensity of the irradiated light from the light source is The light modulation frequency is configured to be changed at the same frequency as the gas modulation frequency and with a phase relationship different from the gas modulation operation, and the gas modulation frequency is changed with respect to the output signal from the absorbance detector. By performing synchronous detection rectification and smoothing processing with a synchronous signal representing a modulation operation, a first rectification signal regarding the gas modulation is obtained, and with respect to the output signal from the absorbance detector,
The configuration is configured to obtain a second rectified signal regarding the optical modulation by performing synchronous detection rectification and smoothing processing using a synchronization signal representing the optical modulation operation, and convert the first rectified signal into a second rectified signal.
A gas analyzer characterized in that it is provided with a signal processing circuit having a correction means for dividing by a rectified signal or an equivalent correction means.