JPS6015013B2 - Photoacoustic analyzer signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal processing circuit in photoacoustic analysis that irradiates a sample with light energy and detects the amount of this light energy converted into heat to analyze the sample. The detection signals from the analysis sample and the reference sample are each supplied to a multiplier to obtain autocorrelation and correlation amounts, and these correlation amounts are further input to the arithmetic processing unit via an integrator and an analog-to-digital converter. The present invention relates to a signal processing circuit for a double-light Tokoacoustic analyzer.

A photoacoustic analyzer shines intermittent light onto an analysis sample in a photoacoustic cell, and when the light energy absorbed by the analysis sample is released as thermal energy, the compression waves generated in the atmosphere of the analysis sample are detected using micro-on, etc. The element detects it as an electrical signal,
This is an analyzer that amplifies this, records it, and provides it for analysis.

Here, the detected electrical signal is an alternating current signal that is the same as the intermittent frequency of the light, and it is necessary to extract the alternating current signal component in synchronization with that frequency, and then amplify and rectify the alternating current component to extract it. Therefore, in the slave, the timing of the intermittent light is detected by a chopper that generates intermittent light, and the previously detected AC electric signal is synchronously rectified at the timing of the intermittent light to obtain an output signal. FIG. 1 is a block diagram showing an example of the configuration of this conventional double-light East type photoacoustic analyzer. In the figure, 1 is a light source such as a xenon lamp, 2 is a chopper, 3 is a drive motor, and 4 is a A synchronizing signal generator, 5 an analyzer, 6 a half mirror as a beam splitter, 7 a reference side photoacoustic cell containing a reference sample, 8 an analysis side photoacoustic cell containing an analysis sample to be analyzed, 9 and 10 is an AC amplifier,
11 and 12 are synchronous rectifiers, and 13 is a divider.
In the above configuration, the light emitted from the light source 1 is converted into intermittent light of a predetermined frequency by the chopper 2, and is incident on the spectroscope 5, from which monochromatic light is extracted.

This monochromatic light output is divided into an eastern halo by a half mirror 6, and is irradiated to each of the photoacoustic cells 7 and 8. The reference side photoacoustic cell 7 obtains a reference output using carbon black, a pyroelectronic element, etc. as a reference sample.

The analysis side photoacoustic cell 8 accommodates an analysis sample and obtains an output A. Each output and A is amplified by AC amplifiers 9 and 10, respectively.

On the other hand, the synchronous rectifier 11 uses the synchronous signal of the intermittent light obtained by the synchronous signal generator 4 such as a photocoupler as a comparison signal.
and 12, each output from amplifiers 9 and 10 is now synchronously rectified, respectively. The two synchronous rectified output signals are then input to a divider 13, which corrects the light source intensity by dividing the signal from the analysis sample by the reference signal.

This allows the photoacoustic output of the sample-side detector to be normalized regardless of the light source intensity. By the way, a photoacoustic signal is a signal that is generated when the energy of light absorbed by a sample is converted into heat inside the sample, and that heat energy is transmitted to the surrounding gas via the sample surface, causing the pressure of the gas to fluctuate. .

Therefore, there is a time delay between light irradiation and conversion into a photoacoustic signal, and the signals on the reference side and analysis side include this delay. This time delay is caused by the photoacoustic cell itself and by the physical properties of the sample, such as thermal conductivity, density, relaxation time of excitation energy, etc., and the latter is an important item in the analysis of the sample. Incidentally, the time delay caused by the former photoacoustic cell itself can be substantially canceled out by accommodating the same reference sample in the analysis-side acoustic cell 8 and adjusting the positions of both outputs Ao and A.

FIGS. 2A and 2B show an example of a detector for a photoacoustic analyzer.

This detector is composed of an analysis side photoacoustic cell 7 and a reference side photoacoustic cell 8. The analysis-side photoacoustic cell 7 and the reference-side photoacoustic cell 8 each include a sample chamber and a reference chamber. R1 and R2 are sample chambers, and these sample chambers R1
, R2 each contain a sample to be analyzed, for example, analysis sample S
I and reference sample S2 are arranged, and a light transmission window W1 for irradiating light energy to these samples S1 and S2.
, W2 are provided. The samples S1 and S2 are stacked on the sample stands D1 and D2, respectively, so that the sample chambers R1 and
It is placed in R2 and can be replaced by removing sample stages D1 and D2. Sample stages D1 and D2 are shown in Figure 2B.
The two may be integrally formed as shown in the figure, or may be separate bodies (not shown). V1, V
2 is a sealing element, for example an O-ring. Samples that can be analyzed with a photoacoustic analyzer may be any solid, powder, liquid, etc. Specifically, various rigid bodies, oxide or sulfide powder such as cadmium sulfide powder, holmium oxide powder, zirconium , thin films such as silicone, characteristic components attached to the surface of objects (such as human scum), drug chips, blood, solutions containing dissolved pigments, and various suspensions.

When the samples SI and S2 are liquids, powders, or substances with unstable physical properties, they are placed in sample dishes (not shown) and placed on the sample stands D1 and D2. However, even if the sample is a solid body such as a rigid body, it is better to avoid placing it directly on the sample stands D1 and D2. C1 and C2 are reference chambers. The reference chambers C1 and C2 are in communication with the sample chambers R1 and R2 via passages L1 and L2, respectively, so that the sample chamber RI and the reference chamber CI, and the sample chamber R2 and the reference chamber C2 are connected to the analysis side, respectively. A photoacoustic cell 7 and a reference side photoacoustic cell 8 are formed. The analysis side photoacoustic cell 7 and the reference side photoacoustic cell 8 are each filled with air or a gas such as nitrogen or helium. Further, thermal flow meter type detection elements GI and G2 are installed at arbitrary locations in the passage LI of the analysis side photoacoustic cell 7 and the passage L2 of the reference side photoacoustic cell 8, respectively. During analysis, the detector configured in this way simultaneously and intermittently irradiates the analysis sample SI and the reference sample S2 with light energy having the same wavelength and energy through the light transmission windows W1 and W2, respectively. Note that this light energy may be applied alternately for a certain period of time. Generally, when a material is irradiated with light energy, a portion of the irradiated light energy is absorbed by the material, and a portion of this absorbed light energy is converted into heat energy.

Furthermore, since each substance has a unique light absorption spectrum corresponding to the condition under certain conditions, the amount of light energy absorbed and the amount of conversion into thermal energy also take on unique values. A photoacoustic analyzer detects this thermal energy as thermal expansion of a substance, that is, a gas around a sample, and analyzes the substance. This thermal energy is transferred to the gas surrounding the samples S1 and S2, respectively, and the pressure in the sample chambers R1 and R2 increases due to thermal expansion of the gas. On the other hand, the reference chambers CI and C2 are not irradiated with light energy. Therefore, the pressures in the reference chambers CI and C2 do not change. Therefore, in the analysis-side photoacoustic cell 7, the sample chamber RI and the reference chamber C
A pressure difference is generated between the sample chamber R2 and the reference chamber C2 in the reference side photoacoustic cell 8, and gas flows from the sample chamber RI to the reference chamber C1 and from the sample chamber R2 to the reference chamber C2. They flow respectively. When the irradiated light is interrupted by the light intermittent chopper 2, the gas flows in the direction in which the pressures in the sample chamber and the reference chamber are balanced, that is, in the direction from the reference chamber CI to the sample chamber RI and from the reference chamber C2 to the sample chamber R2. Therefore, the gas oscillates between the two chambers via the passages L1 and L2, respectively, with the same period as the light interruption period. The period of light intermittent by the light intermittent chopper 2 is IHZ ~ 1000
It is set to a certain value in the HZ range. This vibration is detected as an alternating current electric signal of the thermal flow meter type detection elements GI, G2 arranged in the passages L1, L2, respectively. The resistance changes of the thermal flowmeter type detection elements GI, G2 are taken out as output signals of the above-mentioned analysis-side photoacoustic cell 7 and reference-side photoacoustic cell 8. In the conventional device shown in Fig. 1, the photoacoustic output on the sample side is normalized with respect to the light source intensity.
Regarding the signal delay of the sample itself, we are simultaneously measuring the in-phase output when the photoacoustic output is at its maximum and the output with a 90 degree phase delay.When performing synchronous rectification, the photoacoustic output is at its maximum. The phase is adjusted as follows. Therefore, even though the depth from the sample surface that is effective for measurement changes depending on the intermittent frequency, such phase adjustment when changing the intermittent frequency does not obtain a signal with the truly necessary phase.・There are some difficulties. In order to solve such difficulties,
The inventor passed the reference signal Ao through a phase shifter to change its phase to 9.
The present invention features a signal processing circuit that can measure the signal delay of the sample itself by obtaining a signal delayed by 0 degrees and correlating this 90 degree phase delayed reference signal with the output signal A from the analysis sample. It was proposed earlier as IsoSho No. 53-119918.

To explain this simply, the correlation of the output signal A, with the reference signal and its 90 degree phase delay signal 1. , 12, and the respective autocorrelations l of the signals of the reference signal Ao and its 90 degree phase delay,
A third and a fourth multiplier giving o, lo* are attached, and the output 1 of the first multiplier is divided by the output lo of the third multiplier, and the photoacoustic signal with the normal phase is obtained. A first divider gives an output E, and the output 12 of the second multiplier is divided by the output L* of a fourth multiplier to give a photoacoustic output E2 delayed by 90 degrees from the normal phase. The second divider is equipped with a second divider, and the signal delay function is thus able to perform calculations. According to this, not only can the phase delay of the photoacoustic output of the analysis sample with respect to the reference signal be accurately determined, but also the conventional difficulty of requiring phase adjustment in response to exchange of the analysis sample or change in the intermittent frequency can be solved.

Furthermore, in the signal processing circuit described above, 9
The first requirement is to obtain a signal with a phase delay of 0 degrees, but it is currently technically difficult to realize this circuit, and even higher precision is required, so we decided to The inventor did not use a phase shifter to delay the phase of the reference signal,
A signal processing circuit for a photoacoustic divider that can accurately measure phase lag and obtain a photoacoustic spectrum with optical intensity correction was proposed in Tokubuta No. 53-119919.

In this signal processing circuit, a photoacoustic analyzer obtains photoacoustic outputs by irradiating an analysis sample placed in an analysis-side photoacoustic cell and a reference sample placed in a reference-side photoacoustic cell with intermittent light. In the signal processing circuit, the individual photoacoustic outputs from the photoacoustic cells on the analysis side and the reference side are input to three sets of cascaded circuits of a multiplier and an integrator that provide respective autocorrelation and correlation between both outputs. Then, each of the outputs is supplied to an arithmetic unit via an analog-to-digital converter, and various desired operations are performed based on the correlation.

The signal processing circuit disclosed in Tokukoshi No. 53-11991y converts each correlation output into a digital signal, and inputs the digital signal to an electronic computer to perform various desired calculations. Since computation and transmission require a certain amount of time, the integration time of the integrator, the wavelength reduction speed of the spectrometer, the transmission and reception of signals by the computer, etc. must all be controlled in accordance with the operating speed of the electronic computer. figure.

A control signal is obtained from an electronic computer, and the control signal controls the operation of the integrator and the spectrometer via an integral type analog-to-digital converter. Therefore, the structure of the signal processing circuit becomes complicated, and real-time processing is not possible. In addition, depending on the analytical application, the type of analysis information required is limited, and it is only necessary to supply each correlation output to a device with calculation functions for that purpose, or there is a need to perform special calculations. There are certain cases, and in these cases it is not a good idea to process digital signals with an electronic computer. Therefore, the object of the present invention is to improve the signal processing circuit of the above-mentioned Japanese Patent Application No. 11991/1985, thereby increasing the degree of freedom in analytical calculations and to easily extract analytical information in real time. The present invention provides a signal processing circuit for an acoustic analyzer.

To this end, the present invention provides a photoacoustic analyzer that irradiates intermittent light onto a reference sample placed in a reference-side photoacoustic cell and an analysis sample placed in an analysis-side photoacoustic cell to obtain respective photoacoustic outputs. In the signal processing circuit, a first circuit is supplied with the photoacoustic output from the reference side photoacoustic cell and calculates an autocorrelation of the photoacoustic output, and a first circuit is supplied with the photoacoustic output from the analysis side photoacoustic cell. a second circuit that is supplied with both the photoacoustic outputs from the reference-side and analysis-side photoacoustic cells and calculates the cross-correlation between the photoacoustic outputs of both of the photoacoustic outputs; 3 circuits, and the above-mentioned first
, the outputs from the second and third circuits and the output from the divider are supplied to an arithmetic unit for calculating desired analysis information.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

An embodiment of the photoacoustic analyzer of the present invention is shown in FIG.

In the figure, the configuration up to photoacoustic cells 7 and 8 is the same as in FIG. 1, so the same reference numerals are used and the explanation thereof will be omitted. In FIG. 3, 9A, 10A are front layer AC amplifiers, 9B, 108 are main AC amplifiers, 14, 15,
16 is a multiplier, 17, 18, 19 are constant time integrators, 30
is a divider. The light emitted from the light source 1 is modulated to a predetermined frequency by a chopper 2, enters a spectroscope 5, and is split into monochromatic light, and then sent to a beam splitter, such as a half mirror 6.
The light beam is divided into equal double light beams and enters a reference side photoacoustic cell 7 using, for example, carbon black as a reference sample and an analysis side photoacoustic cell 8 containing an analysis sample.

Now, if we use the phase of the signal from the reference cell 7 as a reference and the phase difference between this signal and the signal from the analysis cell 8, then the time delay due to the characteristics of the photoacoustic cell is equal for both cells 7 and 8. The phase difference 8 is a time delay resulting from the physical properties of the analysis sample itself. After the signals Ao and A from cells 7 and 8 are amplified by front layer amplifiers 9A and 10A, respectively, they are amplified by main AC amplifiers 9B and 10B to chopper 2.
The signal components having the same frequency as the chopping frequency of are selectively amplified to obtain outputs Eo and E, respectively. Here, the amplifiers 9A, 9
It is assumed that the gains of B, 10A, and 10B are adjusted in advance. Now, simplifying the reference side output Eo, Eo=Aosi
If it is expressed as t of n, then the sample side output E, is E,=A,
Sin(t-0).

Here, A is the optical chopper frequency of the chopper 2, A is the phase difference mentioned above, and A is the amplitude of the outputs Eo and E, which is an amount proportional to the intensity of light. In FIG. 3, a multiplier 14 calculates the autocorrelation of the standard output Eo, a multiplier 15 calculates the cross-correlation between the standard output Eo and the analytical sample output E, and a multiplier 16 calculates the cross-correlation between the standard output Eo and the analytical sample output E, Compute the autocorrelation of .

Fixed time integrators 17, 18 and 19 simultaneously integrate the calculation results from these multipliers 14, 15 and 16 for a fixed time, respectively, to obtain correlation amounts Y and autocorrelation amounts x and Z. For this reason, it is assumed that the constant time integrators 17, 18, and 19 are configured so that their respective integration times are synchronized. If the reference side output Eo=A is squared by inwt and integrated over a fixed time, the autocorrelation amount is denoted by x, then It is proportional to the square of the strength.

Let Z be the autocorrelation amount obtained by squaring the analysis sample side output E, and integrating it over a fixed period of time.
), and Z is also proportional to the desperation of the light source intensity.

In addition, the correlation amount Y obtained by taking the correlation between the reference side output Eo and the analysis sample side output E, and integrating it over a fixed time is Y=nA,
sin's tsin ('s t-8) = to A, (si's tc
oS8 - tSin8 of tCOS of one Sin) Target A, Cosa.

Supplying the autocorrelation amount X and the correlation amount Y to the divider 3,
The precision of light source intensity correction, which is the most basic output of the analyzer1. : Take out a concubine.

From the above, each correlation amount X, Y, and Z and the photoacoustic output 1 are extracted from the signal processing circuit of the present invention and supplied to the necessary square rooter, divider, number calculator, etc. according to the analysis purpose. By doing this, you can extract the data of the required mode in real time. For example, the phase delay of the signal of the analysis sample with respect to the reference signal is determined as Y▽every=COS8.

The difference spectrum is determined by (no x no Y). Further, by calculating sin6 from cos8 shown above, an output with a phase delay of 90 degrees can be obtained. In other words, this 90
The 0 phase delayed output is obtained by calculating Y'Xtan8. As described above, in the present invention, when configuring the signal processing circuit for the analysis side output and the reference side output of the photoacoustic analyzer,
The autocorrelation × and Z of each output and the correlation Y of each output are calculated separately using a series circuit of a multiplier and an integrator,
The photoacoustic output Y'X for light source intensity correction, which is the most basic output of the analyzer, is calculated by a divider, and these outputs are supplied to any desired external arithmetic circuit, making the configuration of the signal processing circuit even easier. It is simplified, increases the degree of freedom in analysis calculations, and allows analysis results to be easily obtained in real time. According to the invention, each output X, Y, Z of the integrators 17, 18, 19
The following calculation output can be obtained using . [1}
The photoacoustic output 1 after the light source intensity correction, L = Yasuko's photoacoustic output 1, is obtained from the divider 30.

{2} Phase delay of signal of analysis sample with respect to reference sample8
YCos8=Square root circuit that calculates the square root values of their outputs x and Z is connected to the integrators 17 and 19, respectively, and the output of this square root circuit is multiplied by a multiplier to find xZ, and this multiplication A divider performs a division operation of Y no XZ from the output of the integrator 18 and the output Y of the integrator 18.

'3' Difference spectrum between the photoacoustic output on the reference side and the photoacoustic output on the analysis side (NoX and NoY) Square root circuits are connected to the integrators 17 and 19, respectively, and NoX and NoY are determined.

A subtracter is connected to this square root circuit, and a subtraction operation of (No.times., No.Y) is performed. '41 900 Phase delayed output sin8 Obtained from COSa.

Wind The ratio between the photoacoustic output on the reference side and the photoacoustic output on the analytical side is determined by dividing the outputs of the integrators 17 and 19 and finding the square root of this division value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an example of a conventional photoacoustic analyzer, and FIGS. 2A and 2B are plan views showing the configuration of an example of a detector used in the photoacoustic analyzer of the present invention. -x sectional view and FIG. 3 are block diagrams showing one embodiment of the signal processing circuit of the photoacoustic analyzer of the present invention. 1. ．． ．． ．．・．． Light source, 2... Drive motor, 3.
...Chopper, 4...Synchronization signal generator, 5.
...Spectrometer, 6...・Half Mira, 7・・
...Reference side photoacoustic cell, 8. ．． ．． ．． ．． ．． Analysis side photoacoustic cell, 9A, 10A... Front layer AC amplifier, 9
B, 10B... Main AC amplifier, 9, 10...
・AC amplifier, 11, 12...Synchronous rectifier, I
3...Divider, 14, 15, 16...
Multiplier, 17, 18, 19...Integrator, 30.
...divider. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Photoacoustic analysis in which a reference sample placed in a reference side photoacoustic cell and an analysis sample placed in an analysis side photoacoustic cell are irradiated with intermittent light to obtain respective photoacoustic outputs. In the signal processing circuit of the device, a first circuit that is supplied with the photoacoustic output from the reference side photoacoustic cell and calculates an autocorrelation of the photoacoustic output;
a second circuit that is supplied with the photoacoustic output from the analysis-side photoacoustic cell and calculates an autocorrelation of the photoacoustic output; and a second circuit that is supplied with both the photoacoustic outputs from the reference-side and analysis-side photoacoustic cells. and a third circuit for calculating the cross-correlation between both of these photoacoustic outputs, and each output is independently taken out from the first circuit, the second circuit, and the third circuit. signal processing circuit. 2. A photoacoustic analyzer according to claim 1, wherein the first, second and third circuits each include a cascaded circuit of a multiplier and an integrator. signal processing circuit. 3. In the signal processing circuit for a photoacoustic analyzer according to claim 1 or 2, the light intensity correction is performed based on each output of the first circuit, second circuit, and third circuit. Photoacoustic spectrum of the subsequent analysis sample, phase delay of analysis side photoacoustic output with respect to reference side photoacoustic output, difference spectrum between reference side photoacoustic output and analysis side photoacoustic output, reference side photoacoustic output and analysis side photoacoustic output 1. A signal processing circuit for a photoacoustic analyzer, comprising an arithmetic circuit configured to output at least one of the ratios as an arithmetic result.