JPH0227617B2 - NIJUHENCHOMAIKUROHARENZOKUBUNSEKIHOHOOYOBISOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the development and improvement of a method for continuously measuring the concentration of a substance that provides absorption from a differential absorption curve using a magnetic field sweep (see Japanese Patent Application Laid-open No. 74489/1983).

The method of JP-A-53-74489 aims to continuously measure the concentration of a substance from differential absorption lines obtained by magnetic field sweeping, especially differential absorption lines obtained by EPR measurement of gas-phase paramagnetic substances. This method combines Zeeman modulation (modulated magnetic field) for spectrum detection with magnetic field switching to convert an intermittent measurement method into a continuous measurement method. Therefore, in that case, the objects to be observed are limited to only molecules that have a magnetic moment. This means that the stable molecules in the gas phase that can be detected are O ₂ ,
This means that it is limited to NO, NO ₂ , and ClO ₂ , and there is a problem that the types of target gases to which the method and apparatus can be applied are extremely small, making it impossible to use it for multiple purposes. As long as the spectrum obtained by sweeping the magnetic field is targeted, this point is the same even if an electric field switch is used. Furthermore, the electric field switch does not act on _O2 . Also, EPR of NO ₂
In the signal, the peak-to-peak interval of the first-order differential curve is nearly 280G, and it is relatively difficult to perform a magnetic field switch of several hundred Gauss at a speed exceeding 5Hz.

The purpose of the present invention is to provide a method and apparatus that enable a wide variety of molecules to be measured, solve the above-mentioned problems, and enable continuous measurement with excellent long-term stability. .

All polar gas molecules give a rotational spectrum, which is detected by a microwave spectrometer or microwave cavity spectrometer. Spectra are obtained by frequency sweep or electric field sweep. For these devices, according to the invention, a double modulation is carried out, either with Schüttarch modulation or with source modulation or a combination of both, one at a high frequency f ₁ (for example 100kHz) and the other at a low frequency. f ₂ (e.g. 10Hz)
Set to . The modulated signal of the gas to be measured detected by the detector is first passed through a phase detector set to _f1 . If f ₂ is not applied, the output of the phase detector will give a first-order differential absorption curve when frequency swept or voltage swept. The difference between the maximum value I ₂ and the minimum value I ₁ of this differential absorption curve (I ₂ −
I ₁ ) is proportional to the concentration of the gas to be measured. Therefore
When multiplied by f ₂ , the modulation amplitude of f ₂ is determined by the interval between frequencies ν ₂ and ν ₁ (ν ₂ - ν ₁ ) that gives its maximum and minimum peaks I ₂ and I ₁ , or the interval between voltages E ₂ and E ₁ ( _E2 − _E1 )
Set to correspond to The _f2 component of the signal passes through the phase detector and is processed using a differential sample-and-hold integrator with an appropriate trigger circuit to account for baseline fluctuations at the output of the phase detector. Try to obtain (I ₂ − _{I 1} ) continuously without being affected.

An apparatus for carrying out the method of the invention described above will be described below with reference to the drawings.

FIG. 1 shows a Schüttarch microwave cavity spectrometer showing a first embodiment of the present invention. In FIG. 1, microwaves generated from a microwave source 1 pass through a microwave circuit 2 and a portion thereof is supplied to a Schüttarch cavity resonator 4. In FIG. The microwave circuit 2 is a bridge circuit using a hybrid T or a homodyne detection circuit composed of a main arm and a reference arm. A portion of the microwaves that have been multiple-reflected inside the detector 4 returns to the microwave circuit 2, is combined with a portion of the microwaves from the microwave source 1, and enters the detector 5. The oscillation frequency of the microwave is locked by a frequency control circuit 6 to the resonant frequency of the Schüttark cavity resonator.

At this point, electric field sweeping is used to draw the absorption spectrum of the gas within the sample cell 4. For example, in Japanese Patent Publication No. 55-44904, the resonant frequency of the cavity resonator is set in advance in the vicinity of the absorption signal using a variable termination, and then the Schüttark DC voltage is swept, and the absorption signal is used as the output of the phase detector and the second Obtain it in the form shown in the figure. However, in the current case, a microwave bridge circuit or a homodyne detection circuit with a reference arm is used to obtain high sensitivity, so it is sensitive to ambient disturbances such as temperature and vibration. This results in long-term fluctuations, and the long-term stability of the device is significantly impaired. Therefore, if the Schüttarch DC voltage is fixed at E ₂ and the gas is continuously measured (monitored) as the change in I ₂ over time, fluctuations in the baseline due to imbalance in the microwave circuit will be reflected as is. . Therefore, as a practical gas monitor, unless the problem of long-term fluctuations in the baseline is solved, the advantage of increasing sensitivity using a microwave bridge will hardly be realized.

This problem is solved according to the invention by using a doubly modulated Schutarch cavity. That is, f ₁ is applied to the electrode plate 30 of the Schüttarch cavity resonator 4.
The Schüttarch modulated power supply 7 of _f2 and the Schuttarch modulated power supply 8 of f2 are coupled via a coupler 9. As mentioned above, f ₁ is a high frequency for signal detection, centered at voltage 0, and is a rectangular wave or sinusoidal wave modulation having an appropriate amplitude. Also, f ₂ is a low frequency and the voltage is (E ₁
+ _E2 )/2 is the center value, and ( _E2 - _E1 ) is the amplitude (see Figure 2). f ₂ is preferably a rectangular wave, but may also be a sine wave. The absorption signal subjected to Schütarch double modulation passes through the detector 5 and the phase detector ₁ at f1.
1 for phase detection. However, the component of frequency f ₂ is 1
1. If f ₂ is a rectangular wave, the waveform of the absorption signal at the output end of 11 will be as shown in FIG. Its frequency is f ₂ and I ₁ ,
I ₂ corresponds to I ₁ and I ₂ in FIG. 2. This means that f ₂ is the central value (E ₁ + E ₂ )/2, and the amplitude (E ₂ −
It is easy to understand from E ₁ ). f ₂ is for example
It can be set to an appropriate value between 100 and 1 Hz.

The reason why the waveform in FIG. 3 is not a rectangular wave but has a delay is due to the time constant of the phase detector 11. By processing _the signal _shown in FIG. can be obtained continuously. That is, by using, for example, a differential sample-and-hold integrator 21 consisting of a parallel circuit consisting of a gate G and an integrating circuit R, C, and a differential amplifier, as shown in FIG. 4a, as shown in FIG. 4b. On one channel, gate G2 is opened for a certain period of time when the signal indicates I ₂ to integrate I ₂ , and on the other channel, gate G 1 is opened for a certain period of time when the signal indicates I ₁ and I ₁ is integrated. The timing for opening the gate is determined by a trigger circuit 20 taken out from the modulated power source 8 of _f2 . Here, the differential sample-and-hold integrator 21 includes a gate time setting section and a gate sweeping section for opening the gate for an arbitrary time. After calculating the difference between the integral values of both channels, it is transmitted to the recorder 2 through the amplifier 22.
3, the value of (I ₂ −I ₁ ) is drawn continuously.

This device does not require the DC voltage sweep mechanism used in Japanese Patent Publication No. 55-44904.
It does not require a static magnetic field, which requires a large device like No. 74489, making it particularly suitable for practical use.

FIG. 5 shows an example of continuous measurement of trace amounts of formaldehyde obtained by the above-mentioned Scheutark microwave cavity analyzer. As is clear from Figure 5, even though a microwave bridge circuit or a homodyne detection circuit using a reference arm is used, the long-term stability is extremely high, and the stability sensitivity has been greatly improved. I'm watching.

The sampling system used in the measurement example in Figure 5 is shown in Figure 6.
Shown in the figure. Formaldehyde standard gas (nitrogen base gas) generated by the standard gas generator 100 is constantly allowed to flow to the exhaust port 104. Part of the standard gas is passed through the needle control valve 105 and then sent to the oil rotary pump 107.
Continuously flow through the sample cell at a reduced pressure of about 1 Torr. In FIG. 5, formaldehyde is mixed into the base gas stream at point A and stopped at point B. The subsequent response is also a repetition of ON-OFF of the contamination. In the example shown in FIG. 5, the total sample pressure in the reduced pressure sampling line section from the needle valve 105 to the discharge port 108 is set to 0.6 Torr.

FIG. 7 shows the relationship between the formaldehyde concentration in the base gas nitrogen and the recorder response of the detected signal. It is clear that the two have a good linear relationship and have sufficient quantitative properties.

FIG. 8 shows a second embodiment of the device of the present invention, in which one of the double modulations is set to a relatively high frequency f ₁ and the other to a relatively low frequency f ₂ as described above. In this case, the modulation amplitude of f ₂ is set to correspond to the maximum (maximum) - minimum (minimum) value of the phase detection signal output of f ₁ (value on the horizontal axis that gives), and the signal output of f ₂ is characterized in that it is processed using a differential sample-and-hold integrator 21.

This example is a microwave spectrometer using a double modulation Scheduling cell. In this case, the sample cell 4 is not a cavity resonator, but a single-path ordinary wavelength cell (e.g. CHTownes, AL
Schawlow, “Microwave Spectroscopy”, Mc
(See Grow—Hill, New York, 1955, p. 265)
It is.

Normally, to observe a spectrum with a microwave spectrometer, a microwave source 1 is used to sweep the microwave frequency. The absorption signal of the gas to be measured that has undergone Schützarch modulation at f ₁ passes through the detector 5 and is phase-detected by the phase detector 11 . Now, assuming that f ₂ has never existed before, the signal output at the output terminal 11 has a first-order differential form with respect to the sweep frequency as shown in Figure 9, which is similar to Figure 2. . By the way, when an electric field Ea is applied to the gas molecules to be measured, the center frequency ν ₀ of the absorption line is shifted by Δν according to the effective formula Δν˜(dν ₀ /d _E ) _E=Ea/2 ^Ea due to the Schüttarch effect.

Therefore, according to this effective formula, for ν _S that is near ν ₁ and satisfies the relationship ν _S ν ₁ , ν ₁ = ν _S +
Scheutark voltage E ₁ that satisfies △ν ₁ , ν ₂ = ν _S + △ν ₂ ,
E ₂ can be chosen (v ₁ , v ₂ are given in Figure 9). Therefore, f ₂ is the center voltage (E ₁ + E ₂ )/2,
Set the amplitude to be (E ₂ - _{E 1} ). When multiplied by f ₂ in this way, the modulated signal of f ₂ passes through 11, and the signal is sent to the trigger circuit 20, as described above.
Processing is performed using a differential sample-and-hold integrator 21 to obtain the value (I ₁ −I ₂ ).

In this case, the spectrum linearity obtained by sweeping the frequency will be as shown in Figure 10a, and if the frequency is fixed at ν _S and the sample gas is turned on and off, it will be as shown in Figure 10b. Continuous measurement is possible. In these cases, ₂
Since the integration is performed while taking the difference between the outputs of points (for example, ν ₁ and ν ₂ ), baseline drift and long-term noise disappear, resulting in extremely improved stability.

A third embodiment of the device of the invention is shown in FIG. In FIG. 11, the dual modulation device consists of an f ₁ modulation power source 7 and an f ₂ modulation power source 8 as described above.
f ₁ of the gas to be measured at the output end of the phase detector 11
When sweeping the microwave frequency, the modulation signal of
Obtained as shown in the figure. Therefore, the modulation power source 8 applies source modulation of f ₂ to the microwave source, characterized in that the modulation amplitude corresponds to (v ₂ -v ₁ ). Furthermore, the dual modulation signal thus obtained is processed using a differential sample-and-hold integrator 21 to obtain the value of (I ₂ -I ₁ ). In this device, the microwave spectrum for frequency sweep is as shown in Figure 10a, and when the frequency is fixed and a specific absorption line is continuously monitored, it is as shown in Figure 10b. This results in significantly greater long-term stability compared to conventional devices.

As mentioned above, the dual modulation spectroscopy according to the present invention is an evolution and improvement of the continuous measurement method shown in JP-A-53-74489. Coupled with (1) the range of applicable gases has increased significantly, covering almost all stable molecules. (2) Microwave cavity spectrometers, which greatly improved the long-term stability of microwave spectrometers and increased their sensitivity; (3) Microwave cavity spectrometers or microwave spectrometers that (4) Microwave cavity spectrometers do not require sweeping of static magnetic fields or sweeping of electrostatic fields to obtain spectra, simplifying the equipment; (5) Zeeman Since Schüttarch modulation or source modulation is used instead of modulation, there are significant advantages such as the ability to easily apply large modulations. Furthermore, the microwave cavity spectrometer and microwave spectrometer of the present invention described above are devices that realize these advantages.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the apparatus for carrying out the method of the present invention, Fig. 2 is an absorption curve when double modulation is not applied, and Fig. 3 is an absorption curve obtained by double modulation. , Fig. 4 is a diagram of the principle of the differential sample-hold integrator and its operating waveforms, Fig. 5 is an example of continuous measurement of trace amounts of formaldehyde using the apparatus shown in Fig. 1, and Fig. 6 is a diagram showing the measurement example of Fig. 5. Figure 7 shows the sampling system of the sample used.
FIG. 8 is a block diagram showing the second embodiment of the apparatus of the present invention, and FIG.
The figure shows an absorption curve in the case of no double modulation in the embodiment of Fig. 8, Fig. 10 shows an example of measurement results obtained by the embodiment of Fig. 8, and Fig. 11 shows the absorption curve of the third embodiment of the present invention. FIG. 2 is a block diagram showing an embodiment. 1...Microwave source, 2...Microwave circuit,
4...sample cell, 5...detector, 6...AFC,
7, 8...Modulated power supply, 9...Coupler, 10...Terminal member, 11...Phase detector, 20...Trigger circuit, 21...Differential sample-hold integrator,
22...Amplifier, 23...Recorder, 30...
Scheutark electrode, 100...Standard gas generator, 1
04,108...Discharge port, 105...Needle control valve, 107...Oil rotary pump.

Claims (1)

[Claims] 1 Relatively high signal detection frequencies f ₁ and f ₁ for the sample containing the target substance introduced into the sample cell
The microwave absorption of the sample is detected while applying dual torque modulation at a relatively low frequency _f2 with a modulation amplitude set to correspond to the difference between the maximum and minimum values of the phase detection signal output. Continuous double modulation microwave that continuously measures the concentration of the target substance by obtaining an absorption signal that fluctuates at f ₂ and continuously obtaining the difference between the maximum and minimum values of this absorption signal. Analysis method. 2. The analysis method according to claim 1, wherein the modulation amplitude of the relatively low frequency _f2 is set so as to maximize the difference output value. 3 A sample cell having a Schütztag electrode, a microwave source coupled to the sample cell, and a relatively high signal detection frequency f ₁ applied to the Schütztalk electrode.
and a comparatively low frequency f ₂ dual modulation source whose modulation amplitude is set to correspond to the difference between the maximum and minimum values of the f ₁ phase detection signal output applied to the Schüttarch electrode or microwave source, and the sample cell. a phase detector that detects the frequency f ₁ for signal detection from the microwave absorption detector, and a phase detector that is connected to the phase detector to detect the frequency f ₂ .
A dual modulation microwave continuous analyzer comprising a differential sampling-hold integrator that provides the difference between the maximum and minimum values of , and a display device that displays the output of the differential sampling-hold integrator.