JPS5824203Y2 - optical analyzer - Google Patents

Description

[Detailed Description of the Invention] This invention relates to intermittent light flux in an optical analysis device, particularly in a chemical analysis device that applies optical properties.

In chemical analyzers that apply optical properties, an AC conversion method is used to convert the optical properties of a test substance into an electrical signal in order to improve the sensitivity and stabilize the measurement.
Conventional mechanical or electrical choppers often distort the conversion waveform or generate pulse-like noise at the moment of switching, impeding the sensitivity and stability of analysis.

In addition, in the case of an incomplete waveform like the one mentioned above, increasing the conversion frequency will make the waveform distortion worse, so in the end, the conversion frequency cannot be raised sufficiently, and even if an AC conversion method is adopted, instability such as drift will not occur. It was often difficult to increase the photoelectric output of the remaining detectors.

For example, Figures 1 and 2 are examples of non-dispersive continuous infrared gas analyzers that have been widely used in the past. They adopt an AC conversion system in which the optical paths of two light sources are interrupted by a mechanical beam chopper, and are turned on by power source 1. The output light beams from the light sources 2 and 3 are taken out from the output holes of the masks 4 of the light sources 2 and 3, and are interrupted by a mechanical beam chopper 5 driven by a motor M. This intermittent light is sent to the sample cell 6, The transmitted light from each cell is detected and compared by a detector 8 of a condenser microphone type, for example, and is transmitted to a preamplifier 9a.
, main amplifier 9b, and then displayed and recorded on the recorder 10, and the output waveform is adjusted to be a sine wave. However, as shown in FIG. If the intermittent frequency of the light is increased, the detected waveform by the detector 8 will be distorted, and pulse-like noise will be generated at the moment of switching between intermittent and intermittent light. If the target beam chopper is driven by a motor to intermittent the beam, the phase of the light entering the detectors on the sample cell side and the reference cell side will be out of phase, and furthermore, mechanical vibrations may adversely affect the detectors. This has been a major obstacle to improving sensitivity and stability.

The purpose of this invention is to provide a new optical analysis device that eliminates the above-mentioned defects.

According to this invention, a liquid crystal element is used to interrupt the light beam irradiated onto the sample of the optical analyzer or the light beam from the sample. Various defects such as cases can be eliminated.

As shown in Figure 5, the light transmission characteristics of liquid crystals are such that at wavelengths of 400 OA or more, the transmittance when an electric field is applied is significantly lower than the transmittance when no electric field is applied; By increasing the voltage, it can be reduced to 0.5% or less, and the temporal response characteristics are sufficiently fast, so by installing it at any position in the optical path and intermittent the optical path, the intermittent frequency of the light beam can be made wider than before. It is possible to obtain an AC output waveform with an ideal pulse waveform even when the temperature rises to a certain temperature, and it is possible to obtain a remarkable effect in stabilizing analysis and improving sensitivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows an embodiment of the device in which the present invention is applied to a NOx gas analyzer using the chemiluminescence method, in which 11 is a reaction tank for converting NO gas into NO2 gas, 12 is a sample gas introduction pipe,
13 is an active gas 03 introduction pipe, 14 is a reaction product gas discharge pipe, 15 is an optical filter for cutting interference wavelengths, and an NO optical filter is provided at the tip of the pipe 12.13.
React NO and 03 at the tip of tube 12.13,
The structure is such that chemiluminescence generated during this reaction is taken out of the reaction tank 11 through a filter 15.

16 is a charging conversion device such as a photomultiplier tube or a photoelectric element;
17 is a liquid crystal element that controls transmission of light from the reaction tank 11 to the photoelectric conversion element 16.

Reference numeral 18 denotes a power supply for driving the liquid crystal element, which opens and closes the liquid crystal element 17 by generating a pulse voltage having an appropriate amplitude, frequency, and pulse width depending on the liquid crystal element used.

19 is an amplifier, and 20 is a recording device.

Note that a synchronous demodulator 21 is installed before or after the amplifier 19.
may be provided, and the output of the photoelectric conversion element 16 during the period when the liquid crystal element 17 is open, that is, the period when the applied voltage is zero (or when a voltage at a lower level is applied) may be extracted.

In this case, the synchronous demodulator 21 can be used as a reference wave by using the negative phase voltage E of the output E of the pulse power source 18 directly or by converting it to an appropriate voltage level. This means that it can be shared for control.

Furthermore, depending on the type of demodulator, the common mode voltage E can also be used as a reference wave.

The liquid crystal element 17 is arranged so that the film surface of the element is not perpendicular to the optical axis but is inclined as shown in the figure, and the angle of inclination can be further adjusted.

Furthermore, since the liquid crystal element 17 is a fixed element having no movable parts, the parts 11 to 17 can be housed compactly in the housing H.

Next, the operation of the apparatus shown in FIG. 4 will be explained.

First, in the reaction tank 11, the NO in the sample gas entering from the tube 12 is
A part of the activated gas 03 entering from the tube 13 reacts as follows to produce chemiluminescence.

NO+03 →NON Senkuru 2, NO word →NO2
+h ν ・ ・ ・ ・ ・ ・ ・ (1n(N
Since the intensity of this light emission is proportional to the mass flow rate of NO in the reaction tank 11, it passes through the interference wavelength light cut filter 15, passes through the liquid crystal element 17, and is projected onto the charge conversion element 16. .

The light transmittance of liquid crystal is determined by the applied voltage and the wavelength of light as shown in Figure 5, so the charging conversion device 1 for chemiluminescence (wavelength 5900 to 25000) generated during the reaction of NO- + NO2.
The transmission to 6 can be turned on and off by changing the voltage applied to the liquid crystal.

In this case, the light flux intermittent operation by the liquid crystal element 17 is sufficiently rapid compared to, for example, a conventional mechanical type, and provides extremely sharp intermittent characteristics of rising and falling edges, and does not generate pulse noise during switching.

FIG. 6 shows an example of this experiment, where the horizontal axis shows time and the vertical axis shows charging output, and the transient time is, for example, within 0.02 seconds.
Even if the intermittent frequency is set to around 50, an ideal pulse waveform without any disturbance can be obtained, and the intermittent frequency can be further increased, especially when a cholesteric nematic transition liquid crystal element is used.

Therefore, according to this invention, the difficulty of increasing the low frequency width below 20 stops as in the past is solved, and it is possible to easily obtain a charging output exceeding about 50 stops, making it easy to increase the S/N ratio. The ratio is also improved, and a great effect can be obtained on increasing/decreasing and stabilizing the analysis results.

Furthermore, the discontinuity effect is greater when the relative angle of the liquid crystal film to the optical path is not perpendicular but oblique, and the discontinuity effect will be defined as (on transmittance - off transmittance)/on transmittance.

is obtained. Figure 7 shows an experimental example of the relationship between the angle α between the optical axis X and the liquid crystal film and the transmittance in the off state. ing.

This is considered to be due to a directional scattering phenomenon caused by the molecular arrangement when voltage is applied.

As can be seen from Figure 5, when a voltage is applied, liquid crystals do not transmit light at all, but only slightly, but by arranging the liquid crystals at an angle to the optical path, the directionality of the scattering phenomenon of the liquid crystals can be improved. That is, the optical path of the transmitted light is changed, and the light entering the detector is further reduced, so that the light transmittance when a voltage is applied becomes even smaller than the transmittance when no voltage is applied.

Therefore, the liquid crystal film is disposed not at right angles to the optical path but at an angle as shown in FIG. 4, which provides better luminous flux intermittent characteristics and improves the S/N ratio of photoelectric output.

Although the embodiments of the present invention have been described above, the present invention can also be applied to general analyzers that measure the amount of light, such as ordinary dispersion-type absorption or emission spectrophotometers, atomic absorption spectrophotometers, and others. can.

Furthermore, various modifications and combinations of the configuration of the embodiment are possible. Two or more series of elements 11 to 15 and 17 to 18 are provided, and the respective optical gates are alternately operated (or at different frequencies). ) The light may be opened and closed and projected onto a common charging conversion device, and the output of the photoelectric conversion device may be taken out for each series using a synchronous demodulation method or a filter and displayed and recorded.

[Brief explanation of drawings]

1 and 2 are diagrams showing an example of a conventional optical analysis device, FIG. 3 is a diagram of the output waveform of the detector in the device shown in FIGS. 1 and 2, and FIG. Figure 5 showing an example
7 to 7 are explanatory views of the operation of the apparatus shown in FIG. 4. In the figure, 1... power supply, 2, 3...
Light source, 5... Luminous flux chopper, 6, 7...
...Sample, reference cell, 8...Detector, 11...
...Reaction tank, 12 ... Sample gas introduction tube, 1
3... Active gas inlet pipe, 14... Reactive gas outlet, 15... Filter, 16...
・Photoelectric conversion device, 17...Liquid crystal element, 18...
...Pulse power supply, 19...Amplifier, 20.
... Recording device, 21 ... Synchronous demodulation device,
L... Luminous flux.

Claims (1)

[Scope of utility model registration request] In a device that analyzes substances by detecting the transmitted light flux from the sample or the light emitted by the sample itself, a liquid crystal element is placed at any position in the optical path of the light irradiating the sample or in the optical path from the sample to the detector, with its film surface The liquid crystal element is fixedly disposed obliquely to the optical path, and a predetermined periodic electric signal is applied to the liquid crystal element to change the optical characteristics and intermittent the output luminous flux of the liquid crystal element.
An optical analysis device characterized in that an output electrical signal of a charging conversion device that detects light from a sample is thereby converted into an alternating current waveform of a pulse waveform.