JPS59162425A - Phase compensating type ratio spectrophotometer - Google Patents

Abstract

PURPOSE:To decrease errors accompanied by phase deviation, by detecting a specified phase difference between sample light intensity and reference light intensity, performing specified electric processing of the detected signal, thereby compensating the phase shift of the detected signal. CONSTITUTION:Light emitted from a light source 1 becomes sample luminous flux 13 and reference luminous flux 14 through plane mirrors 2 and 3 and concave mirrors 4 and 5. The luminous fluxes 13 and 14 pass a sample cell 15 and a reference cell 16, are alternately inputted to a monochrometer 11 through plane mirrors 6 and 7, a rotary sector 8, a concave mirror 9, and a plane mirror 10, and are received by a detector 12. Its output becomes DC signals S' and R' through amplifiers 17 and 18 and synchronous rectifiers 19 and 20. Both signals S' and R' are guided to differential amplifiers 21 and 23 directly and through a differential circuit 22. Signals S and R, from which noises are removed, are sent to a divider 24. The value of a ratio S/R is obtained and recorded in a recorder 25. Since the phase shift of the detected signal is corrected and the noises are offset to each other out, errors due to the phase shift can be decreased.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an infrared spectrophotometer using a double beam ratio (electrical direct ratio) method, and particularly in the phase detection method, it is possible to detect phase shifts caused by rapid absorption, etc. This invention relates to a phase-compensated ratio-type spectrophotometer that minimizes noise associated with noise.

As is well-known to Toyo Mameyo, a double-beam spectrophotometer alternately injects light into the sample to be measured and the standard sample (or an empty cell), and combines the sample light that has completely passed through the sample to be measured with the standard sample. The transmittance of the sample is determined by measuring the intensity of the transmitted reference light (also called standard light) and comparing the sample light intensity with the reference light intensity. The signal processing method in such a double-beam spectrophotometer, that is, the typical method for automatically outputting sample transmittance, is the optical method widely used in infrared region spectrophotometers. There are three methods: the target zero level method, the recently developed electrical direct ratio method, and the automatic gain adjustment method.

In the optical zeroing method, the sample light and the reference light attenuated by a mechanical attenuator are alternately switched, and the reference light intensity (Io) is
We extract an AC signal with an amplitude proportional to the difference (to-r) between By adjusting the dimmer in this way, the amount of attenuation (t', b movement of the dimmer) is automatically controlled. Since the change in the transmittance of the sample is proportional to the transmittance, the change in the transmittance of the sample can be recorded by recording the movement of the attenuator.

The optical zero level system as described above is the best in terms of signal utilization and stability, but on the other hand, it has the following various drawbacks. First of all, in Era 1, the transmittance of 111 degrees was greatly influenced by the mechanical strength of the dimmer itself and the accuracy of its linear system, so it was difficult to measure the spectral light at a high degree of effectiveness. Moreover, it is difficult to obtain it stably. In addition, related to this, there are problems such as unevenness in the recirculation of the drive servo motor for moving the wedge-shaped diaphragm normally used in dimmers, and errors in the linearity of the potentiometer that detects the entire position of the wedge-shaped diaphragm. As a result, the amount of movement of the aperture and the amount of light attenuation are not necessarily proportional.
Transmittance measurement accuracy often decreases. Furthermore, since the optical system is included in the servo loop, the signal becomes complicated and
The configuration of the device is also complicated and expensive, and there are drawbacks such as low responsiveness. In addition, when the absorption by the sample is large, the sample light intensity is close to zero, and the reference light intensity is also close to zero, resulting in a small loop gain, which reduces reliability and decreases the light intensity. The accuracy of the optical instrument itself decreases when the amount of light attenuation is extremely large ('T, that is, when the absorption of the sample is extremely large), so these factors combine to significantly reduce the measurement stability when the absorption is large. There is a problem of deterioration.

On the other hand, the automatic gain adjustment method does not use a dimmer, but uses a time-sharing optical path switching means such as a dark full-sector mirror that cuts both the sample light and the reference light, so that the reference source intensity is always constant. This method automatically adjusts the gain of the signal processing system, such as the gain of the detector and the gain of the amplifier, to maintain a constant value. Since this corresponds to the ratio, that is, the transmittance, the transmittance of the sample light can be directly obtained by sample-holding and outputting the output of the amplifier corresponding to the sample light. In this method, the entire electrical signal system is placed within this loop, especially when using a detector whose gain can be controlled, such as a photomultiplier tube, and controlling the gain of the detector by feeding back to the detector. Because the linearity and stability of detectors and amplifiers do not affect the indication, it is possible to determine the temperature of high sheaths, and also because it does not use a dimmer or mechanical servo system, and it has absolute zero Almost all of the drawbacks of the optical zero system are eliminated. However, infrared spectrophotometers that perform analysis in the infrared region have no choice but to use a thermal detector such as a thermocouple, which is difficult to adjust the sensitivity of, so it is difficult to adjust the sensitivity. Even if a thermal detector is used to control the gain of the amplifier, it is not a control force control method, and even if a thermal detector is used to control the gain of the amplifier, the Since the response speed is extremely slow and the time constant is extremely large, the output waveform of the detector does not correspond to the waveform of the change in the light passing through the optical path switching means, making it difficult to put it to practical use as an automatic gain A adjustment method. Met.

Similarly to the automatic gain adjustment method, the electrical direct ratio method does not use a dimmer and includes a component corresponding to the sample light intensity obtained from the photodetector and a component corresponding to the reference light intensity. This is a method in which the signals are amplified in a mixed state using the same amplifier, the subsequent components are electrically separated, and the ratio of both components is electrically calculated. This method combines a frequency component detection method and a phase detection method by separating the sample light intensity component and reference light intensity component from the output of the intensifier.
Although they are broadly classified into the following types, all of them allow signal component separation even when using a thermal detector such as a thermocouple, and therefore can be used in a spectrophotometer for the area outside the door.

Conventional phase detection methods in the electrical direct ratio (1/geo) method include, for example, infrared spectrophotometers described in Japanese Patent Publication No. 47-3798 and Japanese Patent Application Laid-Open No. 57-52832. .

The former uses two sector mirrors for beam splitting and beam recombination, and the latter uses one sector mirror for beam combining.
The sample light and reference beam are arranged so that they have a phase difference of 90°.
Served. By synchronously rectifying this output, the DC signal and reference source corresponding to the sample source can be obtained! Obtain the DC signal corresponding to i'ii k, calculate the ratio of the two, and obtain the desired S
Outer values are required. By the way, in general, when wavelength scanning is performed after spectroscopic analysis, the symmetry of the detector waveform during one cycle is lost when the absorption of the sample is large. It can be seen that the absorption casts a shadow on both the reference source and the sample 5u and influences the output waveform of the detector during one cycle. In such cases, the phase detection method has the drawback that the collapse of the output waveform gives a large curvature (Σ) to the phase, which ultimately results in a measurement error.To explain this in more detail,
When absorption is large, it accompanies wavelength scanning! & Normally, the change in light intensity is rapid, which causes a slope in the sample light intensity during one cycle. Since the time constant of a detector, especially a thermal infrared detector such as a thermocouple, is large, its output signal is considered to have the effect of integrating the entire intensity waveform of the incident light. If the sample light intensity is tilted, the center of the output waveform will shift from the center of the input sample light intensity waveform, and as a result, the phase difference between the output sample light intensity component and the reference source intensity component will shift from 90°. Errors occur. In addition, absorption by water and CO2 in the air affects the strong antireflection waveform of the light incident on the detector itself, causing the output signal of the detector to collapse and causing a phase shift as described above, resulting in a total measurement error.

In order to eliminate errors caused by such phase shifts by slowing down the wavelength scanning time, the slope of the absorption spectrum is determined using a differentiating circuit.1. A method has already been proposed in which when the slope exceeds a certain value, the drive speed of the recorder is reduced to prevent phase shift. In addition to the disadvantage that the scanning time for the entire wavelength range is inevitably long, there is also the disadvantage that the configuration becomes complicated because it is necessary to control the drive of the recorder.

OBJECTS OF THE INVENTION An object of the present invention is to provide a spectrophotometer that completely eliminates the drawbacks of the optical zero position method and the conventional phase detection method as described above. In particular, in phase detection spectrophotometers, it compensates for phase shifts that occur in regions with steep absorption ridges.
The present invention provides a phase compensation type ratio spectrophotometer that minimizes the occurrence of errors caused by the deviation. Furthermore, the present invention focuses on the fact that the above-mentioned phase shift is proportional to the change in the light energy entering the detector, and aims to completely compensate for the phase shift by electrical processing.

In order to achieve the above object, the spectrophotometer according to the present invention has the following features:
The signal of the sample light intensity component and the signal of the reference light intensity component are extracted from the detector with a certain phase difference, and this detector output is synchronously rectified to correspond to the DC signal corresponding to the sample light intensity and the reference light intensity. In a ratio type spectrophotometer that obtains a DC signal corresponding to the sample intensity and calculates the S/R value by calculating the ratio of the two, a first synchronous rectifier obtains a DC signal corresponding to the sample intensity; a second synchronous rectifier to obtain the signal;
A differentiating circuit for differentiating the outputs from these two synchronous rectifiers; a first differential amplifier whose inputs are the output of the differentiating circuit and the output of the first synchronous rectifier; a second differential 1-so-1 corner unit having the output of the rectifier as an input;
It comprises a divider for calculating the ratio of the two outputs of the first and second differential amplifiers; and a recorder for displaying and recording the output of the divider.

EXAMPLE An example of the present invention will be described in more detail below with reference to the drawings. 1 and 2 are block diagrams showing the optical system and electrical processing system of a spectrophotometer according to the present invention, respectively. First, the configuration of the optical system will be explained with reference to FIG. 1.

In FIG. 1, reference numeral 1 denotes an infrared light source consisting of a d-bar, a Nernst heating element, etc., and the light from the light source 1 is passed through a pair of optical systems consisting of a plane mirror 2 and a concave mirror 4, and a plane mirror 3 and a concave mirror 5. , the light beam is divided into two light beams: a sample light beam 13 and a reference light beam 14. The sample light beam 13 and the reference light beam 14 reflected by the concave mirrors 4 and 5 are converged on the sample cell 15 and the reference cell 16, respectively, and after passing through both cells, are reflected by the plane mirror 6.7 and reach the rotating sector 8. Sector 8 has a predetermined pattern of reflective portions, transmitting portions, and blocking portions, as will be described later.
The bundle 13 and the reference beam 14 are alternately guided into the same beam.

The same source from sector 8 is reflected by concave surface @ 9 and focused into the entrance slit of monochromator 11 via plane mirror 10 . The monochromatic light that is separated by the monochromator 11 and taken out from the exit slit enters the detector 12, where it is converted into an electrical signal.

Although the above sector 8 is not particularly shown, the quadrant is a reflection (mirror) part, the other quadrant is a transmission part, and the residual semicircle is a blocking (mask) part, so the detector 12 From this, a signal as shown in FIG. 3 is obtained. The signal component (R) of the reference source intensity is between 0 and 90 degrees where the reflection (mirror) part of the trench 9 and sector 8 is in the optical path, and the signal component (R) of the reference source intensity is between 90 and 180 degrees where the transmitted part of the sector is in the optical path. is the signal component (S) of the sample source, and the blocking (mask) part is in the optical path.
The dawn component (D) is sequentially obtained between .degree.

The output from this detector 12 is synchronized, the S component and the R component are extracted, and the ratio of both components is calculated. Normally, the desired Nishiki value can be obtained by calculating the value, but as mentioned above, in places where there is significant absorption, the sample light and reference light are affected and the output waveform of the detector is distorted, resulting in noise due to phase shift. occurs. In the case of rapid absorption, the sample light component (S) from the detector has an attenuated sinusoidal waveform as shown in FIG. 4, and the phase shift resulting in noise is proportional to this energy change. The change in energy can be expressed by the slope θ of the straight line t filled with the peaks of the attenuation waveform in Fig. 4, or in other words, by the change in the synchronous rectified output corresponding to each signal component. By subtracting it from the signal component, a correct value that fully compensates for the phase shift can be obtained. Next, an electrical processing system including all of these points will be explained with reference to FIG.

The output signal from the detector 12 is amplified by a preamplifier 17 and a main amplifier 18 before entering a first synchronous rectifier 19 and a second synchronous rectifier 20. The first synchronous rectifier 19 is 90°~
The second synchronous rectifier 20 performs synchronous rectification in the phase range of 180° and outputs a DC signal S/T corresponding to the sample light intensity, while the second synchronous rectifier 20 performs synchronous rectification in the phase range of 00 to 90° to output the reference light intensity. outputs a DC signal k corresponding to . These signals Sol/ contain noise due to phase shifts. The output signal S' of the first synchronous flow converter 19 enters one input terminal of the first differential multiplier 1[1Δ converter 21 and is also sent to the differentiating circuit 22. Also, the output signal R' of the synchronous rectifier 20 of Ki 2 is the second differential amplifier'? It enters one input terminal of the M converter 23 and is also sent to the differentiating circuit 22. Then, the output from the differentiating circuit 22 is transmitted to the first and second differential amplifiers 21.2.
3, the differential signals are each subtracted from the signal S'lR', and the true sample light component S(!: reference light component R from which the noise has been removed is determined.
The second difference, the output ratio of the dynamic amplifiers 21 and 23, is determined by the divider 24, and the desired S/R value is displayed and recorded on the recorder 25. Although not particularly shown, a synchronous wave for synchronous rectification is obtained by a synchronous wave generator such as a photocoupler attached to the sector 8.

Effects of the Invention As described above, according to the spectrophotometer of the present invention, changes in energy are detected using a total differential circuit in the phase detection method, and differential components are subtracted from the sample source signal and reference optical signal after synchronous rectification. Since the phase shift is compensated for and the noise is completely canceled out, the following advantages can be obtained.

First, since a phase detection method is employed, the disadvantages inherent in optical nulling methods can be avoided. There is no reduction in measurement accuracy due to the processing accuracy of the dimmer 9, uneven rotation when driving the dimmer, or errors in the linearity of the potentiometer for detecting the position of the dimmer. Furthermore, since it is a ratio (direct ratio) method, there is no need for a servo loop system, which simplifies signal processing and device configuration.

Second, since the phase shift caused by rapid absorption is compensated for, the generation of noise due to the phase shift, which was unavoidable with conventional phase detection methods, can be minimized.

Tip 9: Conventionally, noise generation due to phase shifts caused by energy changes was 30 to 50% in the output, but in the present invention, this has been reduced to about 1%. For this reason, it has become possible to draw spectra that were previously hidden by absorption of H2O and the like.

Third, since the above phase shift is compensated for electrically, there is no need to slow down the recorder's transmission speed in regions with rapid absorption, as in the conventional method, and therefore the scanning time over the entire wavenumber range is reduced. There is no disadvantage that the compensation system becomes complicated due to the longer length.

As a result, it was possible to obtain a phase detection type spectrophotometer that generates almost no noise even when the wave number range of 4000 to 400 Crr1 is set for a total of 2 minutes.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the optical system of the phase-compensated Sioux spectrometer according to the present invention, Fig. 2 is a block diagram showing the electrical processing system, and Fig. 3 shows the output signal from the detector. FIG. 4 is a waveform diagram for explaining phase compensation according to the present invention. ”...Light source, 2.3.6.7.10...Plane mirror, 4,
5゜9...Concave+nLy2.8...Sector, ll・
... Monochromator, ]2... Detector, 13... Sample f flux, 14... Reference light flux, 15... Sample cell, 1
6... Reference cell, 17... Preamplifier, 18...
Main amplifier, 19... first synchronous rectifier, 20... second synchronous rectifier, 21... first differential amplifier, 22
・Differential circuit, 23...Second differential amplifier, 24...
- Divider, 25...Recorder. Applicant: JASCO Corporation

Claims (1)

[Claims] A signal of the sample light intensity component and a signal of the reference source intensity component are extracted from the detector with two constant phase differences, and the output of the detector is synchronously rectified to generate a direct current corresponding to the sample light intensity. In a ratio type spectrophotometer that calculates the S/R value by calculating the ratio between the DC signal and the output signal corresponding to the signal and reference light intensity, a first synchronous rectifier that obtains the DC signal corresponding to the sample light intensity; A second synchronous rectifier to obtain a DC signal fr corresponding to the reference light intensity; a differentiation port and path for differentiating the outputs from the two synchronous rectifiers; input the output of the differentiation circuit and the output of the first synchronous rectifier; a first differential amplifier whose inputs are the output of the differentiating circuit and the output of the second synchronous rectifier; A phase-compensated ratio spectrophotometer comprising: a divider for determining the ratio of two outputs; and a recorder for displaying and recording the output of the divider.