JP2012026957A - Spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of a calculation value of absorbance or the like by reducing noise when a wavelength scanning speed is low.SOLUTION: When a wavelength scanning speed is set to be low (Yes in S10) and a level of a sample side measurement signal obtained by detecting transmitted light of a sample to be measured is lower than a threshold (Yes in S13, S14 and S15), a rotational speed of a sector mirror for dividing monochromatic light into a sample side beam and a reference side beam is lowered (S16). Thereby, switching frequency of sectors per unit time is reduced and a rate of waste periods in which effective data cannot be collected before and after the switching is reduced. Consequently, the number of target data to be added per the same time can be increased (namely, addition time is extended) and a noise level can be reduced. When the level of the sample side measurement signal is equal to or above the threshold, the influence of increase of 1/f noise may exceed, and thereby the rotational speed of the sector mirror is maintained at a normal speed.

Description

  The present invention relates to a spectrophotometer, and more particularly to a double beam type spectrophotometer that divides measurement light into two directions of a sample side optical path and a reference side optical path by a rotating sector mirror, a beam splitter, or the like.

  The spectrophotometer has a double beam method and a single beam method depending on the configuration of the optical path. The double beam method is generally more advantageous than the single beam method in terms of analysis accuracy because the influence of fluctuations in the light amount of the light source can be canceled in principle in the course of calculating the absorbance.

  As a double beam type spectrophotometer, a configuration in which monochromatic light extracted by a spectroscope (monochromator) is divided into a sample-side light beam and a reference-side light beam using a rotating sector mirror is well known. For example, in a spectrophotometer disclosed in Patent Document 1 or the like, monochromatic light is alternately distributed into a sample-side light beam and a reference-side light beam by a sector mirror that is rotationally driven at a constant speed, and the sample-side light beam irradiates the sample to be measured. Then, the reference-side light beam is applied to a reference sample that does not contain the component to be measured, for example, only the solvent. Thus, the light transmitted through the sample to be measured and the light transmitted through the reference sample are alternately introduced to one photodetector, and the photodetector detects a signal corresponding to each transmitted light. In addition, a light-shielding portion that shields light is provided integrally with the sector mirror, and dark signals due to dark current and the like when light is not incident on the photodetector are also periodically measured as the sector mirror rotates. It is like that.

  FIG. 12 is a plan view of a general sector mirror used in the double beam spectrophotometer as described above. In the sector mirror 8, reflecting mirrors 82, openings 83, and light shielding portions 84 are alternately provided around the axis 81. Now, assuming that the sector mirror 8 is installed so that the monochromatic light beam extracted from the spectroscope is positioned at a position L indicated by a dotted line in FIG. 12, the sector mirror 8 is moved to the position L during one rotation. The opening 83 → the light shielding portion 84 → the reflecting mirror 82 → the light shielding portion 84 → the opening portion 83 → the light shielding portion 84 → the reflecting mirror 82 → the light shielding portion 84 comes in order. That is, the mode of the sector mirror 8 is, as shown in FIG. 13 (a), passing (S) → light shielding (DS) → reflection (R) → light shielding (DR) → passing (S) → light shielding (DS) → reflection. It switches in the order of (R) → light shielding (DR). The sample-side light beam is irradiated to the sample to be measured during the passage (S), and the reference-side light beam is irradiated to the reference sample during the reflection (R) period. In addition, no light enters the photodetector during the light shielding (DS, DR) period. As a result, in the photodetector, the sample-side signal is time-divisionally transmitted during the passage (S) period, the reference-side signal is transmitted during the reflection (R) period, and the dark signal is transmitted during the light-shielding (DS, DR) period. It is obtained by.

  An example of the change in the detection signal is shown in FIG. Normally, when the sector mirror 8 rotates, the signal changes greatly before and after the switching of each sector. However, due to the restriction of the frequency response of the photodetector and the subsequent electric circuit, the rise and fall of the signal change is caused. The descent is dull. The detection signal is sampled at a predetermined sampling period and converted into digital data in the A / D converter, but accurate data cannot be obtained in a range where the signal is not settled at the sector switching. Therefore, only data obtained in each data collection period shown in FIG. 13C is treated as valid data, and data generated in other periods is rejected. In FIG. 13C, Ds is the sample-side signal data collection period, Dr is the reference-side signal data collection period, Dds is the sample-side dark signal data collection period, and Ddr is the reference-side dark signal data collection period. is there.

  In the case of a single detector configuration in which the sample-side light beam and the reference-side light beam are introduced into one photodetector, the dark current is approximately the same for the sample-side dark signal and the reference-side dark signal. Are virtually indistinguishable. On the other hand, in the case of a double detector configuration in which the sample-side light beam and the reference-side light beam are respectively introduced into different photodetectors, the dark current is different for each photodetector, so the sample-side dark signal and the reference-side dark signal are Are treated separately.

  In general, the rotational speed of the sector mirror is about several tens of Hz (for example, the power supply frequency of an AC power supply), and the data sampling cycle is much shorter than that. For this reason, a lot of data is obtained in each data collection period, and noise reduction processing such as integration averaging processing is performed on the data. For example, when performing integration averaging processing, noise superimposed on the signal is inversely proportional to the square root of integration time (in the case of digital data, the number of data to be integrated). Therefore, it is effective to extend the integration time to reduce noise.

  In the spectrophotometer as described above, wavelength scanning is performed by a spectroscope in order to acquire an absorption spectrum over a predetermined wavelength range, and this wavelength scanning speed can be generally changed. When the wavelength scanning speed is high, the wavelength changes for each cycle shown in FIG. 13A, whereas when the wavelength scanning speed is low, the wavelength is the same for a plurality of cycles. Data obtained in the same data collection period can be integrated. That is, when the wavelength scanning speed is low, the integration time can be extended. However, as described above, since effective data cannot be obtained at the sector switching, there is much data that is actually wasted even if the integration time is extended. Therefore, even in the conventional spectrophotometer, noise can be reduced when the wavelength scanning speed is low as compared with the case where the wavelength scanning speed is high, but the effect is not necessarily exhibited sufficiently.

  In addition, for example, when the light absorption in the sample to be measured is large, the noise level of the sample-side measurement signal and the noise level of the reference-side measurement signal are greatly different. In such a case, the higher noise level is the overall noise level. Will dominate. As a result, the SN ratio of the absorption spectrum calculated from the sample-side measurement signal and the reference-side measurement signal becomes low, which may hinder high-accuracy measurement. The same applies when the noise level of the dark signal is sufficiently low and the noise level of the sample-side measurement signal or the reference-side measurement signal is high. That is, when the difference in noise level between the measurement signals or between the measurement signal and the dark signal is large, there is a problem that the SN ratio of the absorption spectrum is lowered by the signal having the higher noise level, and the measurement accuracy is impaired.

JP 2001-356049 A

  The present invention has been made to solve the above-mentioned problems, and its first object is to improve the measurement accuracy by improving the S / N ratio of the absorption spectrum compared to the conventional case when the wavelength scanning speed is slow. It is to provide a double beam type spectrophotometer that can perform the above.

  The second object of the present invention is that there is a large difference in noise level between the sample side measurement signal and the reference side measurement signal, or there is a large difference in noise level between the dark signal and the sample side measurement signal or the reference side measurement signal. In some cases, it is an object to provide a double beam spectrophotometer that can improve the measurement accuracy by improving the S / N ratio of the absorption spectrum as compared with the conventional case.

According to a first aspect of the present invention for achieving the first object, after monochromatic light is extracted from light emitted from a light source by a spectroscope capable of wavelength scanning, the monochromatic light is converted into a sample-side light beam by a light distribution means. An optical system that alternately distributes light to the reference side light flux and introduces the light flux that passes through the sample to be measured and the reference sample to the photodetector, or splits the monochromatic light into the sample side light flux and the reference side light flux. Any one of the optical systems: an optical unifying unit that alternately guides each light beam passing through the sample to be measured and the reference sample to the detector or an optical system that is introduced into the photodetector through a light shielding unit that intermittently blocks each of the light beams In the double beam type spectrophotometer using
a) a drive source for driving the light distribution means, the light coalescence means, or the light shielding means so as to periodically switch the light flux;
b) when scanning the wavelength of the monochromatic light, the control means for controlling the drive source so as to change the switching speed of the luminous flux according to the wavelength scanning speed;
It is characterized by having.

  Note that the optical union means does not necessarily have to coincide with the optical axes of the two light beams as long as both light beams after the two light beams merge together reach the light receiving surface of one detector. The same applies to the second and third inventions described later.

  In one aspect of the spectrophotometer according to the first aspect of the present invention, the light distribution means includes a sector mirror having a reflecting mirror, an opening, and a shield around a rotation axis, and the control means includes the sector mirror. The drive source for rotationally driving the sector mirror can be controlled so as to change the rotation speed. As the light distribution means, an optical element such as an optical switch can be used.

  According to another aspect of the spectrophotometer according to the first aspect of the present invention, the monochromatic light is divided into a sample-side light beam and a reference-side light beam by a beam splitter, and the light beams transmitted through the sample to be measured and the reference sample are combined with the light. A configuration may be adopted in which the shutters as means are alternately switched to be introduced into one photodetector.

  Furthermore, as another aspect of the spectrophotometer according to the first invention, the monochromatic light is divided into a sample-side light beam and a reference-side light beam by a beam splitter, and the light beams that pass through the sample to be measured and the reference sample are shielded from light. It is good also as a structure which shields periodically by a means and introduce | transduces into a separate photodetector. The light shielding means may be of any structure, such as a member having an opening and a shield around the rotation axis, or an optical switch.

  In the spectrophotometer according to the first aspect of the present invention, for example, when a sector mirror is used as the light distribution means, the control means sets the drive source so as to lower the rotational speed of the sector mirror when the wavelength scanning speed is slow compared to when it is fast. Control. When the rotation speed of the sector mirror decreases, the frequency of switching between the reflecting mirror and the shielding unit and the switching between the opening and the shielding unit per unit time associated with the rotation decreases. Since the signal level changes greatly before and after the switching, the rise and fall of the signal becomes dull due to the restriction of the response speed of the photodetector and the subsequent circuit system, and valid data cannot be collected during that time. On the other hand, in the spectrophotometer according to the first aspect of the invention, when the wavelength scanning speed becomes slow, the frequency of signal switching per unit time decreases, so the proportion of useless periods during which valid data cannot be collected decreases. As a result, the number of data subject to noise reduction processing per unit time increases (for example, the integration time becomes longer), and the noise level can be reduced.

  However, semiconductor elements generally used in electric circuits such as amplifiers have 1 / f noise whose noise level is inversely proportional to the increase in frequency. If the rotation speed of the sector mirror is lowered, this 1 / f noise may increase. For this reason, it is desirable to consider which one of the 1 / f noise increasing effect and the noise reducing effect on the measurement signal with the increase of the noise reduction processing time is superior when the rotational speed of the sector mirror is lowered. Generally, when the light reaching the photodetector is weak and the level of the measurement signal is low, the noise superimposed on the signal by the photodetector or the like is relatively large, which increases the noise reduction processing time. The noise reduction effect on the associated measurement signal is superior.

  Therefore, as a preferred aspect of the spectrophotometer according to the first aspect of the invention, the control means responds to the level of the detection signal from the light detector when the light beam passing through the sample to be measured is incident on the light detector. Thus, it is preferable to determine whether or not it is necessary to change the light beam switching speed according to the wavelength scanning speed. That is, only when the level of the detection signal by the photodetector is below a predetermined threshold, the sector mirror rotation speed is lowered when the wavelength scanning speed is low, and the level of the detection signal by the photodetector exceeds the predetermined threshold. If so, the sector mirror rotation speed may be set as usual regardless of the wavelength scanning speed.

According to a second aspect of the invention made to achieve the second object described above, the measurement light is alternately distributed to the sample-side light beam and the reference-side light beam by the light distribution means, and is transmitted through the sample to be measured and the reference sample, respectively. An optical system that introduces a light beam into one or separate optical detectors, or splits measurement light into a sample-side light beam and a reference-side light beam, and optically combines the light beams that pass through the sample to be measured and the reference sample, respectively. In a double beam type spectrophotometer using any one of the optical systems alternately introduced into one photodetector by means,
a) In one cycle in which the light beam transmitted through the sample to be measured and the light beam transmitted through the reference sample are alternately incident on one or a plurality of photodetectors, the light beam obtained by the photodetector is obtained with respect to the transmitted light beam of the sample to be measured. Noise reduction processing means for performing noise reduction processing on the sample side measurement signal and the reference side measurement signal obtained by the photodetector with respect to the transmitted light beam of the reference sample;
b) controlling the light distribution means or the light combining means so as to change the ratio of the time during which the transmitted light flux of the sample to be measured and the transmitted light flux of the reference sample are incident on the photodetector in the one cycle; Correspondingly, control means for changing the period of the signal of the noise reduction processing target by the noise reduction processing means,
It is characterized by having.

  In one aspect of the spectrophotometer according to the second invention, as the light distribution means, a sector mirror having a reflecting mirror, an opening, and a shielding portion around a rotation axis, and a drive source for rotationally driving the sector mirror, In the sector mirror, the transmitted light flux of the sample to be measured and the transmitted light flux of the reference sample are changed in one cycle by changing the angle occupied in the rotation direction of at least one of the reflecting mirror and the opening. It is preferable that the ratio of the time when the light enters the photodetector is changed.

  In this configuration, in one sector mirror, the angle occupied in the rotation direction of at least one of the reflecting mirror and the opening may be variable, or the angle occupied in the rotation direction of at least one of the reflecting mirror and the opening. It is also possible to prepare a plurality of types of sector mirrors having different from each other, and to replace them appropriately or automatically or manually. In any case, when the sector mirror is rotated at a constant rotational speed, the ratio of the time during which the sample to be measured is irradiated with the light beam and the time during which the reference sample is irradiated with the light beam in one cycle due to the change in the angle. Is changed.

  In addition, when the rotational speed of the sector mirror is variable, especially when the rotational operation from one rotational position to the next rotational position can be performed at a high speed and the sector mirror can be stopped suddenly at a certain rotational position, By the rotation control, the ratio of the time for sending the sample-side light beam and the time for sending the reference-side light beam in one cycle can be changed.

  Conventionally, the noise reduction processing time (number of data subject to noise reduction processing) of the sample side measurement signal in one cycle is the same as the noise reduction processing time (number of data subject to noise reduction processing) of the reference side measurement signal. Also, the time ratio was not changeable. On the other hand, in the spectrophotometer according to the second aspect of the present invention, the noise reduction processing time of the sample-side measurement signal (number of data subject to noise reduction processing) and the noise reduction processing time of the reference-side measurement signal (noise reduction processing) in one cycle. The number of target data) can be changed. As described above, for example, when the integration averaging process is performed as the noise reduction process, the noise level is inversely proportional to the square root of the integration time. Therefore, when there is a large difference in the noise level between the sample-side measurement signal and the reference-side measurement signal, the ratio of the integration time of the measurement signal on the side with the larger noise level is increased. When the time of one cycle is constant, if the integration time of one measurement signal, for example, the integration time of the sample-side measurement signal is increased, the integration time of the other reference-side measurement signal is shortened. As a result, the noise level on the sample-side measurement signal after the integration process decreases, while the noise level of the reference-side measurement signal increases. That is, the noise levels of both of them having a large difference are close to each other, and the overall noise level can be reduced.

  In a preferred aspect of the spectrophotometer according to the second aspect of the present invention, the spectrophotometer further includes noise estimation means for estimating a noise level of a signal obtained by the photodetector, and the control means estimates the noise level by the noise estimation means. Depending on the result, the ratio of the time during which the transmitted light beam of the sample to be measured and the transmitted light beam of the reference sample enter the photodetector in one cycle may be changed.

  According to this configuration, the noise reduction processing time is appropriately adjusted so that the noise level of the sample-side measurement signal and the noise level of the reference-side measurement signal are approximately the same while keeping the cycle time constant. can do. Thereby, the overall noise level can be minimized or close to it.

  As another preferred aspect of the spectrophotometer according to the second aspect of the invention, the control means is adapted to adjust the level of the detection signal by the photodetector when the light beam passing through the sample to be measured is incident on the photodetector. Accordingly, the ratio of the time during which the transmitted light beam of the sample to be measured and the transmitted light beam of the reference sample enter the photodetector in one cycle can be changed.

  As described above, since the noise level is usually relatively high when the signal level is low, the noise level is estimated from the signal level, and the noise level of the sample-side measurement signal and the noise level of the reference-side measurement signal are comparable. Thus, the respective noise reduction processing times can be adjusted appropriately.

  In the spectrophotometer according to the second aspect of the invention, when there is a large difference in noise level between the sample-side measurement signal and the reference-side measurement signal, the ratio of the noise reduction processing time to the measurement signal on the higher noise level side is increased. However, if there is a large difference in the noise level between the sample-side measurement signal and the dark signal, or if there is a large difference in the noise level between the reference-side measurement signal and the dark signal, the same method is applied. By making the noise levels of the measurement signal and the dark signal comparable, the overall noise level can be reduced.

That is, in the third invention made to achieve the second object, the measurement light is alternately distributed to the sample-side light beam and the reference-side light beam by the light distribution means, and the sample to be measured and the reference sample are respectively separated. An optical system that introduces one or more light beams to be transmitted to separate photodetectors, and the measurement light is divided into a sample-side light beam and a reference-side light beam, and the light beams transmitted through the sample to be measured and the reference sample are optically combined. An optical system that alternately introduces into one photodetector by one means, and the measurement light is divided into a sample-side light beam and a reference-side light beam, and light beams that pass through the sample to be measured and the reference sample are detected separately. Any one of the optical systems introduced into the detector and at least one of the optical systems that pass through the sample to be measured and the light beams that pass through the reference sample alternately enter the photodetector. Times, the light flux enters the photodetector. A double beam type spectrophotometer provided with a light shielding means for periodically shielding the light beam on the optical path or blocking each light beam transmitted through the sample to be measured and the reference sample at least once in one cycle. In total
a) a sample-side measurement signal obtained by the photodetector with respect to the transmitted light flux of the sample to be measured in one cycle, a reference-side measurement signal obtained by the photodetector with respect to the transmitted light flux of the reference sample, and Noise reduction processing means for performing noise reduction processing on the dark signal obtained by the photodetector at the time of light shielding,
b) The ratio of the time during which the transmitted light beam of the sample to be measured is incident on the photodetector and the time during which the light is shielded and / or the transmitted light beam of the reference sample is incident on the photodetector in the cycle. And controlling at least one of the light distribution means, the light coalescence means, or the light shielding means so as to change the ratio of the time during which the light is blocked and the time during which the light is blocked, and the noise reduction processing correspondingly Control means for changing the period of the signal subject to noise reduction processing by the means;
It is characterized by having.

  A spectrophotometer according to a third aspect of the present invention provides a sector mirror having a reflecting mirror, an opening, and a shielding portion around a rotation axis as the light distribution means and the light shielding means, and the sector mirror is driven to rotate. An angle that occupies in the rotation direction of at least one of the reflecting mirror and the light shielding part, or at least one of the opening and the light shielding part. By changing the ratio, the ratio of the time during which the transmitted light beam of the sample to be measured enters the photodetector and the time during which the light is shielded in one cycle, and / or the transmitted light beam of the reference sample is detected by the photodetector. The ratio between the time when the light is incident and the time when the light is shielded can be changed.

  In the spectrophotometer according to the third invention, preferably, the spectrophotometer further includes noise estimation means for estimating a noise level of a signal obtained by the photodetector, and the control means is a noise level estimation result by the noise estimation means. The ratio of the time during which the transmitted light beam of the sample to be measured enters the photodetector and the time during which the light is shielded and / or the transmitted light beam of the reference sample enters the photodetector during one cycle. It can be set as the structure which changes the ratio of the time to perform and the time when the light is shielded. Further, the control means transmits the light beam transmitted through the sample to be measured in one cycle according to the level of the detection signal from the light detector when the light beam transmitted through the sample to be measured is incident on the light detector. The ratio between the time when the light is incident on the photodetector and the time when the light is shielded, and / or the ratio between the time when the transmitted light beam of the reference sample is incident on the photodetector and the time when the light is shielded A configuration may be adopted in which the ratio of the time during which the transmitted light flux of the sample to be measured and the transmitted light flux of the reference sample to be changed enters the photodetector is changed.

  According to the spectrophotometer according to the first aspect of the present invention, when performing wavelength scanning over a predetermined wavelength range, when the wavelength scanning speed is slow, even if the time required for measurement is kept the same as in the prior art, the noise reduction processing target is the same per unit time. As the number of data increases, the noise level can be reduced as compared with the conventional method, thereby improving the accuracy of the absorption spectrum.

  Further, according to the spectrophotometers according to the second and third inventions, when the noise level between the sample side measurement signal and the reference side measurement signal is greatly different, the noise level between the sample side measurement signal and the dark signal is greatly different. Or when the noise level of the reference measurement signal and the dark signal is significantly different, the overall noise level can be reduced even if the measurement time is kept the same as before, thereby reducing the absorption spectrum. Accuracy can be improved.

The block diagram of the principal part of the spectrophotometer by 1st Example of this invention. FIG. 3 is a schematic timing chart showing mode transitions associated with rotation of a sector mirror, detection signals obtained by a photodetector, and data collection periods for each signal in the spectrophotometer of the first embodiment. The figure which shows the wavelength transition of a standard scanning speed and the half scanning speed. The control flowchart of the measurement operation | movement in the spectrophotometer of 1st Example. The figure which shows an example of the correspondence of the absorption spectrum in the spectrophotometer of 1st Example, and the rotational speed of a sector mirror. The block diagram of the principal part of the spectrophotometer by 2nd Example of this invention. The top view of two types of sector mirrors used with the spectrophotometer of 2nd Example. FIG. 9 is a schematic timing chart showing mode transitions accompanying rotation of a sector mirror, detection signals obtained by a photodetector, and data collection periods for each signal in the spectrophotometer of the second embodiment. The figure which shows the relationship between the integration time of a sample side measurement signal, the ratio of a reference side measurement signal, and the whole noise level. The figure which shows an example of the correspondence of the absorption spectrum in the spectrophotometer of 2nd Example, and the rotational speed of a sector mirror. The block diagram of the principal part of the spectrophotometer by 3rd Example of this invention. The top view of the conventional common sector mirror. The typical timing diagram which shows the mode transition accompanying the rotation of the sector mirror in a general spectrophotometer, the detection signal obtained by a photodetector, and the data collection period with respect to each signal.

[First embodiment]
A spectrophotometer which is one embodiment (first embodiment) of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of the main part of a spectrophotometer of the double beam / single detector system according to the first embodiment.

  In FIG. 1, light emitted from a light source 1 is introduced into a spectroscope 6 including an entrance slit 2, a diffraction grating 3, an exit slit 4, and a stepping motor 5, and monochromatic light having a predetermined wavelength is extracted from the spectroscope 6. . The stepping motor 5 changes the wavelength of the monochromatic light extracted through the exit slit 4 by changing the angle of the diffraction grating 3 with respect to the incident light that has passed through the entrance slit 2. The monochromatic light extracted from the spectroscope 6 is alternately sent in the direction of the two reflecting mirrors 10 and 11 by the sector mirror 8 that is rotationally driven by the motor 9 at a predetermined rotational speed.

  The sector mirror 8 has the structure shown in FIG. When the opening 83 comes to the irradiation position L of the monochromatic light coming from the spectroscope 6 as the sector mirror 8 rotates, the monochromatic light passes through the opening 83 and strikes the reflecting mirror 11 to become the sample-side light beam Ls. The sample 13 to be measured is irradiated. On the other hand, when the reflecting mirror 82 comes to the irradiation position L of the monochromatic light, the monochromatic light is reflected by the reflecting mirror 82 and hits the reflecting mirror 10 to be irradiated on the reference sample 12 as a reference side light beam Lr. Further, when the light blocking portion 84 comes to the irradiation position L of the monochromatic light, the sample side light beam Ls and the reference side light beam Lr are not present. For example, the sample 13 to be measured is a sample cell filled with a sample solution to be measured, and the reference sample 12 is a sample cell filled with only a solvent. As shown in FIG. 12, the sector mirror 8 has the opening 83, the reflecting mirror 82, and the light-shielding portion 84 at the same rotation angle of 45 ° around the axis 81. Therefore, in one cycle (1/2 rotation period), the period during which light is irradiated to the sample 13 to be measured and the reference sample 12 is equal, and the period during which light is shielded is also equal.

  The reference-side light beam Lr that has passed through the reference sample 12 is reflected by the reflecting mirror 14, and the sample-side light beam Ls that has passed through the sample 13 to be measured is reflected by the reflecting mirrors 15, 16 and introduced into a common photodetector 17. Regardless of the type of light detector 17, an appropriate detector such as a photomultiplier tube, a semiconductor detector such as InGaAs, InAs, or PbS can be used depending on the wavelength band. Of course, a plurality of photodetectors may be switched according to the wavelength.

  A detection signal from the photodetector 17 is amplified by an amplifier (not shown) and the like and then input to an A / D converter (ADC) 18 where it is sampled at a predetermined sampling period and converted into a digital value. As a result, data corresponding to the intensity (light quantity) of the light incident on the photodetector 17 is obtained, and this time-series data is input to the data processing unit 20. The data processing unit 20 selects and classifies necessary data based on a control signal from the control unit 30 that controls the motors 5, 9 and the like, and stores and sorts the necessary data. Further, predetermined calculation processing using the data is performed. By executing the above, the absorbance of the sample to be measured is calculated for each wavelength to create an absorption spectrum.

  The data processing unit 20 and the control unit 30 can be configured around a personal computer, and each function is achieved by executing dedicated control / processing software installed in the personal computer on the computer. be able to. As functional blocks embodied by such software, the data processing unit 20 includes a measurement signal integration processing unit 21, a dark signal integration processing unit 22, a data memory 23, an absorbance calculation processing unit 24, and the like. The measurement signal integration processing unit 21 integrates data obtained during the data collection period Ds of the sample side signal and data obtained during the data collection period Dr of the reference side signal, and calculates an average value thereof. . The dark signal integration processing unit 22 integrates data Dds obtained during the data collection period of the sample-side dark signal and data obtained during the data collection period Ddr of the reference-side dark signal, and calculates an average value thereof. It is.

  A characteristic measurement operation in the spectrophotometer of the present embodiment will be described with reference to FIGS. In this spectrophotometer, in order to measure an absorption spectrum in a predetermined wavelength range (for example, λ1 to λ2), wavelength scanning is performed so that the wavelength of monochromatic light extracted from the spectroscope 6 changes by predetermined wavelength steps in the predetermined wavelength range. Is done. This wavelength scanning speed (amount of wavelength shift per unit time) is not one but a plurality of kinds. FIG. 3 is a diagram showing a wavelength shift between a standard scanning speed (A) and a half scanning speed (A / 2). Even in the case of the same wavelength step Δλ, if the scanning speed is halved, the time for staying at one wavelength is doubled.

  FIG. 2 is a schematic timing chart showing the mode transition accompanying the rotation of the sector mirror 8, the detection signal obtained by the photodetector 17, and the data collection period for each signal. (A) to (c) are wavelengths. When the scanning speed is A, (d) to (f) are cases where the wavelength scanning speed is A / 2. However, as will be described later, when the wavelength scanning speed is A / 2, the timings (d) to (f) are not necessarily reached, and the timings (a) to (c) may be reached. The timing shown in FIGS. 2A to 2C is the same as the timing shown in FIG.

  FIG. 4 is a control flowchart of the measurement operation in the spectrophotometer of the first embodiment. The measurement operation will be described with reference to FIG.

  Prior to the execution of measurement, the control unit 30 determines whether or not the set wavelength scanning speed is low (step S10). Here, for simplicity of explanation, it is assumed that there are only two types of wavelength scanning speeds, A and A / 2, and that the former is a normal speed and the latter is a low speed. When the wavelength scanning speed is set to the normal speed, the control unit 30 sets the rotation speed of the sector mirror 8 to the normal speed (for example, 60 Hz), drives the motor 9, and starts scanning at the wavelength scanning speed: A. The wavelength scanning as shown in FIG. 3 is started from the wavelength λ1. At the same time, the data processor 20 performs a photometric operation (step S20).

  That is, with the switching of the mode of the sector mirror 8 as shown in FIG. 2A, the detection signal as shown in FIG. The measurement signal integration processing unit 21 integrates a plurality of data obtained during the data collection period Ds of the sample side measurement signal and a plurality of data obtained during the data collection period Dr of the reference side measurement signal shown in FIG. The obtained value is stored in the data memory 23. On the other hand, the dark signal integration processing unit 22 integrates and averages a plurality of data obtained during the dark signal data collection periods Dds and Ddr shown in FIG. 2C and stores the obtained values in the data memory 23. . Thus, data of each signal is collected until the scanning end wavelength λ2 is reached. This is the same as the measurement operation in the conventional spectrophotometer.

  On the other hand, if it is determined in step S10 that the wavelength scanning speed is low, the controller 30 first sets the rotation speed of the sector mirror 8 to the normal speed (60 Hz) and drives the motor 9 (step S11). At a scanning speed of A / 2, the wavelength scanning as shown in FIG. 3 is started from the scanning start wavelength λ1 (step S12). At the same time, the data processing unit 20 starts a measurement operation, that is, data collection (step S13).

  That is, with the switching of the mode of the sector mirror 8 as shown in FIG. 2A, the detection signal as shown in FIG. The measurement signal integration processing unit 21 integrates a plurality of data obtained during the data collection period Ds of the sample side measurement signal and a plurality of data obtained during the data collection period Dr of the reference side measurement signal shown in FIG. The obtained value is stored in the data memory 23. On the other hand, the dark signal integration processing unit 22 integrates and averages a plurality of data obtained during the dark signal data collection periods Dds and Ddr shown in FIG. 2C and stores the obtained values in the data memory 23. . In this case, as described above, the time for staying at the same wavelength is twice that when the wavelength scanning speed is A, so the number of data obtained for the same wavelength is doubled.

  When the integrated average value of the sample-side measurement signal is obtained, the measurement signal integration processing unit 21 compares the value with a predetermined threshold value (step S14). When the degree of light absorption in the sample 13 to be measured is large and the level of the sample-side measurement signal is low and it is determined that the signal value is smaller than the threshold value, the process proceeds from step S15 to S16. Is set to a low speed (for example, 30 Hz which is 1/2 of the standard speed). On the other hand, when the integrated average value of the sample-side measurement signals is equal to or greater than the threshold value, the control unit 30 sets the rotation speed of the sector mirror 8 to the standard speed (step S17). That is, the rotation speed of the sector mirror 8 is changed according to the magnitude of the integrated average value of the sample side measurement signals.

  When the rotational speed of the sector mirror 8 is halved, the period of each mode of the sector mirror 8 is doubled as shown in FIG. This means that the frequency of signal change accompanying mode switching is halved per unit time. As shown in FIG. 2 (e), when the signal level changes greatly, the waveform becomes dull due to the restriction of the frequency response of the amplifier circuit, etc., but the signal level is stabilized by extending the period of each mode. The period of time is also extended. Therefore, the data collection period for each measurement signal and dark signal is long as shown in FIG. 2 (f), which is longer than twice the data collection period when the rotational speed of the sector mirror 8 is normal. This is because the frequency of signal change associated with mode switching is reduced, and waste of a period during which data cannot be collected before and after the signal change is reduced. As a result, compared to the case where the wavelength scanning speed is A / 2 and the rotational speed of the sector mirror 8 is the normal speed, the number of data obtained for the same wavelength is increased, and the noise can be reduced accordingly. Since the data collection period changes according to the rotational speed of the sector mirror 8, the timing for selecting data in the data processing unit 20 and the timing of the integration averaging process also need to be changed according to the rotational speed of the sector mirror 8. Of course it is.

  Then, the control unit 30 determines whether or not the wavelength scanning is completed (step S18). If the scanning end wavelength λ2 has not been reached yet, the control unit 30 sends a control signal to the motor 5 so as to shift to the next wavelength. The diffraction grating 3 is rotated (step S19). Thereafter, the process returns to step S13, and data collection is executed again. Therefore, the processing in steps S13 to S19 is repeated until the scanning end wavelength λ2 is reached, and the rotation speed of the sector mirror 8 is switched between the normal speed and the low speed depending on whether or not the integrated average value of the sample side measurement signal is equal to or greater than the threshold value. It is done.

  As described above, when the rotational speed of the sector mirror 8 is low, the number of data to be integrated and averaged increases, so that noise reduction is achieved. However, noise near the mode switching frequency associated with the rotation of the sector mirror 8 is not removed. For this reason, when there is a lot of 1 / f noise at a higher level in the low frequency band, if the rotational speed of the sector mirror 8 is lowered, the 1 / f noise may increase and may have an adverse effect. Generally, when the light incident on the photodetector 17 is weak, there is originally a lot of noise, and the noise reduction effect by reducing the rotation speed of the sector mirror 8 as described above is remarkable. Therefore, in the above embodiment, the rotation speed of the sector mirror 8 is lowered only when the wavelength scanning speed is low and the light incident on the photodetector 17 is weak, and the photodetector 17 is low even if the wavelength scanning speed is low. When the light incident on is strong, the rotation speed of the sector mirror 8 is not lowered.

  FIG. 5 is a diagram illustrating an example of a correspondence relationship between the absorption spectrum and the rotation speed of the sector mirror 8. When the absorbance is high, the sample-side measurement signal is low. Therefore, when viewed from the absorption spectrum, the rotation speed of the sector mirror 8 is slow in the wavelength range above a certain absorbance, and in the wavelength range below the absorbance, The rotation speed is a normal speed.

  Of course, if the influence of the 1 / f noise is originally small and the noise reduction effect is better than the increase of the 1 / f noise when the rotational speed of the sector mirror 8 is lowered, it is determined Yes in step S10. Then, the rotation speed of the sector mirror 8 may be set to a low speed and measurement may be executed up to the scanning end wavelength.

  In the above embodiment, in order to realize the double beam system, the monochromatic light coming from the spectroscope 6 is divided into the sample-side light beam Ls and the reference-side light beam Lr using the sector mirror 8 and transmitted through the sample 13 to be measured. The sample-side light beam Ls and the reference-side light beam Lr transmitted through the reference sample 12 are introduced into the photodetector 17, but the structure of the optical system is not limited to this. For example, the monochromatic light is divided into the sample-side light beam Ls and the reference-side light beam Lr using an optical element such as an optical switch, or the monochromatic light is divided into the sample-side light beam Ls and the reference-side light beam Lr by a beam splitter. Alternatively, the light beams may be divided and intermittently shielded by a shutter, and alternately introduced into the photodetector.

[Second Embodiment]
Next, a spectrophotometer which is another embodiment (second embodiment) of the present invention will be described with reference to FIGS. FIG. 6 is a block diagram of the main part of a double beam single detector spectrophotometer according to the second embodiment. Constituent elements that are the same as or correspond to those shown in FIG.

  In this spectrophotometer, the basic optical system is the same as that of the first embodiment, but a sector mirror exchange mechanism 40 capable of exchanging two different types of sector mirrors 8A and 8B is provided. Selects one of the sector mirrors 8A and 8B under the instruction of the control unit 30 and connects it to the shaft of the motor 9 and inserts it into the optical path.

  FIG. 7 is a plan view of two types of sector mirrors 8A and 8B. The sector mirror 8A shown in FIG. 7A is the same as that shown in FIG. 12, and the angles occupied by the reflecting mirror 82, the opening 83, and the light shielding portion 84 around the rotation axis 81 are equal (45 °). Therefore, here, this is called a uniform sector mirror. On the other hand, in the sector mirror 8B shown in FIG. 7B, the angle of the opening 83 is expanded to 90 °, and the angles occupied by the reflecting mirror 82 and the light shielding portion 84 are reduced to 30 ° each. The ratio of the angle occupied by the opening 83 and the reflecting mirror 82 is 3: 1, which is referred to herein as a non-uniform sector mirror.

  In the spectrophotometer of the present embodiment, for example, the person in charge of analysis estimates the degree of light absorption of the sample to be measured to some extent, and inputs the magnitude of light absorption as one of the analysis conditions from an operation unit (not shown) prior to analysis. Set. When the absorbance by the sample to be measured is small, the amount of transmitted light of the sample to be measured 13 is relatively large, and when the absorbance by the sample to be measured is large, the amount of light transmitted by the sample to be measured 13 is relatively Get smaller. When shot noise is the main cause of noise on the measurement signal, the noise level increases when the amount of light incident on the photodetector 17 is small. Therefore, the control unit 30 uses the non-uniform sector mirror 8B when the absorbance is set to be large, and uses the uniform sector mirror 8A when the absorbance is set to be small. The sector mirror exchange mechanism 40 is instructed to do so. In response to this, the sector mirror exchanging mechanism 40 connects the sector mirror to be used to the rotating shaft of the motor 9.

  When the analysis is started, the motor 9 is driven to rotate at a constant speed under the control of the control unit 30, and the sector mirror 8A or 8B rotates at a constant speed (for example, 60 Hz). When the uniform sector mirror 8A is used, the mode transition of the sector mirror 8A accompanying the rotation, the detection signal by the photodetector 17, and the data collection period in the data processing unit 20 are shown in FIGS. As shown. This is the same timing as FIGS. 2A to 2C and FIGS. 13A to 13B, and has already been described.

  On the other hand, when the non-uniform sector mirror 8B is used, the mode transition of the sector mirror 8B accompanying the rotation, the detection signal by the photodetector 17, and the data collection period in the data processing unit 20 are shown in FIG. ) To (f). That is, in the non-uniform sector mirror 8B, since the angle of the opening 83 is wide and the angles of the reflecting mirror 82 and the light shielding portion 84 are narrow, the sample-side light beam Ls is measured in one cycle. The period during which the sample 13 is irradiated becomes longer, and the period during which the reference-side light beam Lr is irradiated onto the reference sample 12 and the light shielding period are shortened. Accordingly, the periods Ds, Dr, Dds, and Ddr for collecting data obtained by digitizing each measurement signal and dark signal also change.

  That is, as described above, when it is estimated that the absorbance of the sample to be measured 13 is large and the noise level of the sample side measurement signal is high, the ratio of the integration time to the sample side measurement signal is increased. This lowers the overall noise level. This will be explained briefly.

When the noise level of the sample-side measurement signal is Ns and the noise level of the reference-side measurement signal is Nr, the noise level Nt of the signal reflecting the absorbance obtained from both measurement signals is
Nt = √ (Ns ² + Nr ² )
It is. As an example, assume that the sample-side measurement signal noise level Ns is 100 times worse than the reference-side measurement signal noise level Nr. That is, Ns = N and Nr = 100 × N.
Consider a case in which the ratio of integration time is changed while keeping the total integration time of both measurement signals equal. For the integration time Ps of the sample side measurement signal and the integration time Pr of the reference side measurement signal,
I = Ps / Pr, Ps + Pr = 1
Then, the integration time Ps of the sample-side measurement signal and the integration time Pr of the reference-side measurement signal are rewritten as follows.
Ps = I / (I + 1)
Pr = 1 / (I + 1)

Therefore, the noise level Nt after the integration time change is
Nt = √ {Ns ² (I + 1) / 2I + Nr ² (I + 1) / 2}
It is. When this is represented by a graph with respect to log (I), it is as shown in FIG. When log (I) = 0, I = 1, that is, when the integration time for the sample-side measurement signal is equal to the integration time for the reference-side measurement signal, and the noise level is near log (I) = 2, that is, I = 100. Is minimized. Thereby, when there is a difference between the noise level of the sample-side measurement signal and the noise level of the reference-side measurement signal, the ratio of the integration time with respect to each measurement signal is changed appropriately instead of 1: 1 to It can be seen that the noise level can be reduced.

  Similarly, when there is a large difference in the noise level between the sample-side measurement signal and the sample-side dark signal, or when there is a large difference in the noise level between the reference-side measurement signal and the reference-side dark signal, these measurement signals The total noise level can be lowered by appropriately changing the ratio of the integration time to the dark signal and the integration time to the dark signal instead of 1: 1.

  Therefore, when the noise level of the sample side measurement signal is higher than the noise level of the reference side measurement signal, and the noise level of the sample side measurement signal is higher than the noise level of the sample side dark side signal or the reference side dark signal, FIG. The non-uniform sector mirror 8B as shown in (b) is used, and the data processing unit 20 performs data processing at the timings shown in FIGS. The overall noise level can be reduced as compared with the case where it is used.

  As described above, the value of I for minimizing the overall noise level, that is, the optimum value of I is determined by the difference between the sample-side measurement signal noise level Ns and the reference-side measurement signal noise level Nr. Therefore, from the viewpoint of minimizing or approaching the overall noise level, the angle of each sector is variable, not the non-uniform rotating sector mirror in which the angle of each sector in the rotation direction is fixed as described above. It is preferable to use a rotating sector mirror having a certain structure and appropriately adjust the integration time of each signal by changing the angle of each sector in real time based on the actually acquired signal.

When the noise level is estimated based on the actually acquired signal, for example, the following can be performed. For example, as shown in FIGS. 8A to 8C, a large number of data can be obtained in each data collection period Ds, Dds, Dr, Ddr while the sector mirror is rotated at a constant speed. The noise level of each data collection period is defined as follows.
N (Ds) = σ (Ds) / (<Ds> − <Dds>)
N (Dds) = σ (Dds) / (<Ds> − <Dds>)
N (Dr) = σ (Dr) / (<Dr> − <Ddr>)
N (Ddr) = σ (Ddr) / (<Dr> − <Ddr>)
Here, σ (X) is a standard deviation of data in the period X, and <X> is an average value of data in the period X.
When four noise levels N (Ds), N (Dds), N (Dr), and N (Ddr) in one cycle are obtained, each data collection of the next cycle is performed so that the ratio of the noise levels is obtained. What is necessary is just to change the angle of each sector, ie, the reflective mirror 82, the opening part 83, and the light-shielding part 84, so that the length of period Ds, Dds, Dr, Ddr may be adjusted.

  Further, as described above, normally, the noise level increases as the absorption by the sample is large and the level of the sample-side measurement signal decreases. Therefore, instead of obtaining the noise level as described above based on the acquired signal, each sector is adjusted so that the length of each data collection period Ds, Dds, Dr, Ddr is adjusted based on the level of the sample-side measurement signal. That is, you may change the angle of the reflective mirror 82, the opening part 83, and the light-shielding part 84. FIG. Although the entire noise level cannot be minimized, a structure in which the uniform sector mirror and the non-uniform sector mirror are exchanged as shown in FIG. As a result, the signal level of the obtained sample-side measurement signal is compared with a threshold value, and a non-uniform sector mirror is selected when the measurement signal is smaller than the threshold value, and a uniform sector mirror is selected when the measurement signal is greater than or equal to the threshold value. It is good to do so.

  FIG. 10 is a diagram showing an example of the correspondence relationship between the absorption spectrum and the sector mirror selection (uniform / non-uniform). When the absorbance is high, the sample-side measurement signal is low. Therefore, in the absorption spectrum, a non-uniform sector mirror is used in a wavelength range above a certain absorbance, and a uniform sector mirror is used in a wavelength range below that absorbance. used.

  In the second embodiment, on the assumption that the sector mirror is rotated at a constant speed, the integration time is changed by changing the angle occupied by each sector in the rotation direction. However, the rotation speed is changed for each sector. When the rotation of the sector mirror can be temporarily stopped when an arbitrary sector has arrived at the irradiation position L of monochromatic light, even if the angle of each sector is the same, the rotation control is performed. The integration time can be adjusted appropriately.

  As in the first embodiment, the configuration of the optical system for realizing the double beam system is not limited to that using a sector mirror that is rotationally driven. For example, a configuration may be adopted in which monochromatic light is divided into the sample-side light beam Ls and the reference-side light beam Lr using an optical element such as an optical switch. Further, as shown in FIG. 11, the monochromatic light is split into two of the sample side light beam Ls and the reference side light beam Lr by the beam splitter 41, and each light beam is intermittently shielded by the shutters 42 and 43, respectively. It can also be set as the structure introduce | transduced into the photodetector 17. FIG. In this example, the shutters 42 and 43 are synchronously driven and rotated by the motor 44. By changing the angle of the light shielding portion in the rotation direction of the shutters 42 and 43, integration of each measurement signal and dark signal is performed. It is possible to adjust the time. In addition, in the case of a shutter that can shield light at an arbitrary timing instead of such a rotary shutter, the integration time of each measurement signal and dark signal can be adjusted by controlling the timing.

  In addition, each of the above embodiments has a single detector configuration, but the present invention can also be applied to a double detector configuration. However, in the case of a double detector configuration, for each photodetector, one cycle of the sample-side signal data collection period and the sample-side dark signal data collection period, the reference-side signal data collection period and the reference-side dark signal data The collection period is one cycle. Therefore, in the case of the first embodiment, the cycle period is changed for each photodetector, and in the case of the second embodiment, the measurement signal data collection period and dark signal data collection within one cycle. The ratio with the period will be changed.

  Moreover, the said Example is an example of this invention, Even if it changes suitably, amends, and is added in the range of the meaning of this invention, it is naturally included in the claim of this application.

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Entrance slit 3 ... Diffraction grating 4 ... Exit slit 5 ... Stepping motor 6 ... Spectroscope 8, 8A, 8B ... Sector mirror 81 ... Rotating shaft 82 ... Reflection mirror 83 ... Opening part 84 ... Light-shielding part 9, 44 ... Motors 10, 11, 14, 15 ... Reflector 12 ... Reference sample 13 ... Measured sample 17 ... Photo detector 20 ... Data processing unit 21 ... Measurement signal integration processing unit 22 ... Dark signal integration processing unit 23 ... Data memory 24 ... Absorbance calculation processing unit 30 ... Control unit 40 ... Sector mirror exchange mechanism 41 ... Beam splitters 42, 43 ... Shutter

Claims (11)

After monochromatic light is extracted from the light emitted from the light source by a spectroscope capable of wavelength scanning, the monochromatic light is alternately distributed into the sample-side light beam and the reference-side light beam by the light distribution means, and the sample to be measured and the reference sample are respectively obtained. An optical system that introduces a light beam that passes through a photodetector, or a detector that splits the monochromatic light into a sample-side light beam and a reference-side light beam, and alternately transmits each light beam that passes through the sample to be measured and the reference sample. In the double beam type spectrophotometer using any one of the optical system that introduces into the photodetector through the light coalescing means that leads to the light or the light shielding means that intermittently blocks each,
a) a drive source for driving the light distribution means, the light coalescence means, or the light shielding means so as to periodically switch the light flux;
b) when scanning the wavelength of the monochromatic light, the control means for controlling the drive source so as to change the switching speed of the luminous flux according to the wavelength scanning speed;
A spectrophotometer comprising: The spectrophotometer according to claim 1, wherein
The light distribution means has a sector mirror having a reflecting mirror, an opening, and a shielding part around a rotation axis, and the control means rotates the sector mirror so as to change the rotation speed of the sector mirror. A spectrophotometer characterized by controlling a driving source to be driven. The spectrophotometer according to claim 1 or 2,
The control means needs to change the light beam switching speed in accordance with the wavelength scanning speed according to the level of the detection signal from the light detector when the light beam transmitted through the sample to be measured is incident on the light detector. A spectrophotometer characterized by determining whether or not. An optical system in which the measurement light is alternately distributed to the sample-side light beam and the reference-side light beam by the light distribution means, and the light beams that pass through the sample to be measured and the reference sample, respectively, are introduced into one or separate light detectors, or Any one of the optical systems in which the measurement light is divided into the sample-side light beam and the reference-side light beam, and the light beams respectively transmitted through the sample to be measured and the reference sample are alternately introduced into one photodetector by the optical coalescing means. In a double beam spectrophotometer using one optical system,
a) In one cycle in which the light beam transmitted through the sample to be measured and the light beam transmitted through the reference sample are alternately incident on one or a plurality of photodetectors, the light beam obtained by the photodetector is obtained with respect to the transmitted light beam of the sample to be measured. Noise reduction processing means for performing noise reduction processing on the sample side measurement signal and the reference side measurement signal obtained by the photodetector with respect to the transmitted light beam of the reference sample;
b) controlling the light distribution means or the light combining means so as to change the ratio of the time during which the transmitted light flux of the sample to be measured and the transmitted light flux of the reference sample are incident on the photodetector in the one cycle; Correspondingly, control means for changing the period of the signal of the noise reduction processing target by the noise reduction processing means,
A spectrophotometer comprising: The spectrophotometer according to claim 4, wherein
The light distribution means includes a sector mirror having a reflection mirror, an opening, and a shielding portion around a rotation axis, and a drive source for rotationally driving the sector mirror. By changing the angle occupied by at least one of the mirror and the opening in the rotation direction, the ratio of the time during which the transmitted light beam of the sample to be measured and the transmitted light beam of the reference sample enter the photodetector in one cycle is changed. A spectrophotometer characterized by that. The spectrophotometer according to claim 4 or 5, wherein
Noise estimation means for estimating the noise level of the signal obtained by the photodetector is provided, and the control means transmits the transmitted light flux of the sample to be measured in one cycle according to the estimation result of the noise level by the noise estimation means. And a ratio of the time during which the transmitted light flux of the reference sample is incident on the photodetector. The spectrophotometer according to claim 4 or 5, wherein
The control means controls the transmitted light beam of the sample to be measured and the reference sample in one cycle according to the level of the detection signal from the light detector when the light beam transmitted through the sample to be measured is incident on the light detector. The spectrophotometer is characterized in that the ratio of the time during which the transmitted light flux enters the photodetector is changed. An optical system that alternately distributes the measurement light into the sample-side light beam and the reference-side light beam by the light distribution means, and introduces the light beams that pass through the sample to be measured and the reference sample, respectively, into separate photodetectors; An optical system that splits the measurement light into a sample-side light beam and a reference-side light beam, and alternately introduces light beams that pass through the sample to be measured and the reference sample, respectively, into a single photodetector by means of optical coalescence, and the measurement light While using any one optical system of the optical system which divides | segments into a sample side light beam and a reference side light beam, and introduce | transduces into a separate photodetector the light beam which permeate | transmits a to-be-measured sample and a reference sample, respectively. The light beam transmitted through the sample to be measured and the light beam transmitted through the reference sample alternately enter the photodetector at least once in one cycle so that the light beam does not enter the photodetector periodically on the optical path. Shield or measure In a spectrophotometer double beam system having a light shielding means for Hay shielding at least once each beam passes through the charge and the reference sample in each one cycle in,
a) a sample-side measurement signal obtained by the photodetector with respect to the transmitted light flux of the sample to be measured in one cycle, a reference-side measurement signal obtained by the photodetector with respect to the transmitted light flux of the reference sample, and Noise reduction processing means for performing noise reduction processing on the dark signal obtained by the photodetector at the time of light shielding,
b) The ratio of the time during which the transmitted light beam of the sample to be measured is incident on the photodetector and the time during which the light is shielded and / or the transmitted light beam of the reference sample is incident on the photodetector in the cycle. And controlling at least one of the light distribution means, the light coalescence means, or the light shielding means so as to change the ratio of the time during which the light is blocked and the time during which the light is blocked, and the noise reduction processing correspondingly Control means for changing the period of the signal subject to noise reduction processing by the means;
A spectrophotometer comprising: The spectrophotometer according to claim 8, wherein
The light distribution means and the light shielding means include a sector mirror having a reflecting mirror, an opening, and a shielding part around a rotation axis, and a drive source for rotationally driving the sector mirror. By changing the angle occupied in the rotation direction of at least one of the reflecting mirror and the light shielding part, or at least one of the opening and the light shielding part, the measurement is performed in one cycle. The ratio between the time when the transmitted light beam of the sample is incident on the photodetector and the time when the light is shielded, and / or the time when the transmitted light beam of the reference sample is incident on the photodetector and the time when the light is shielded A spectrophotometer characterized by changing the ratio of The spectrophotometer according to claim 8 or 9, wherein
Noise estimation means for estimating the noise level of the signal obtained by the photodetector is provided, and the control means transmits the sample to be measured in one cycle according to the noise level estimation result by the noise estimation means. The ratio between the time when the light beam is incident on the photodetector and the time when the light is shielded; and / or the ratio between the time when the transmitted light beam of the reference sample is incident on the photodetector and the time when the light is shielded; A spectrophotometer, characterized by changing. The spectrophotometer according to claim 8 or 9, wherein
According to the level of the detection signal from the light detector when the light beam transmitted through the sample to be measured is incident on the light detector, the control means transmits the light beam transmitted through the sample to be measured in one cycle. Changing the ratio between the time when the light is incident on the detector and the time when the light is shielded and / or the ratio between the time when the transmitted light beam of the reference sample is incident on the light detector and the time when the light is shielded A spectrophotometer characterized in that the ratio of the time during which the transmitted light beam of the sample to be measured and the transmitted light beam of the reference sample enter the photodetector is changed.

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