JPH02201231A - Spectrophotometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a spectrophotometer, and more particularly to a spectrophotometer having a structure in which a dispersive element for wavelength scanning or wavelength setting is rotated by a motor.

(Prior Art) A sine bar mechanism has traditionally been used as a wavelength scanning mechanism for spectrophotometers using a diffraction grating. The bar is pushed and moved, and there is an advantage that the amount of rotation of the feed screw has a linear relationship with the wavelength, but since the feed screw is used, it is difficult to rapidly feed the wavelength. In recent years, with the spread of computer technology, it has become easy and quick to convert the amount of rotation of a pulse motor into an arbitrary function value. The advantage of having a linear relationship between the amount of rotation and the wavelength has faded, and the difficulty of high-speed wavelength feeding has become a problem. Spectrophotometers in which the element is directly rotated via a speed reduction mechanism have come into use.

In spectrophotometers in which the spectroscopic element is directly rotated via a deceleration mechanism, the relationship between the amount of rotation of the motor and the wavelength is not linear even when a diffraction grating is used as the dispersive element. In this case, the relationship between the rotation angle θ from the reference position of the diffraction grating and the wavelength λ is expressed as d λ= −COSφ111nθ−(1) where d1 is the grating constant of the diffraction grating and n is the diffraction order. As shown in Fig. 4, φ is half of the angle between the incident light on the diffraction grating G and the diffracted light, and 1/2 of the angle that the input slit of the spectrometer makes with respect to the center of the diffraction grating.
It is. Since the relationship between the rotation angle of the diffraction grating and the wavelength is as shown in equation (1), in a spectrophotometer of the type in which the dispersive element is directly rotated via a deceleration mechanism, the rotation amount X of the dispersive element drive motor is On the other hand, λ=Ks+npx However, θ= p x ・・'■
The amount of rotation of the drive motor is converted into a wavelength value using a ROM in which a relational table is written.

In the above equation (2), p is a constant determined by the deceleration mechanism, but K is the lattice constant of the diffraction grating as shown in equation (1),
It includes quantities related to the position of optical elements such as the input and output slits of the spectrometer, and these include manufacturing and assembly errors of the spectrometer. Each one is slightly different. However, when manufacturing a spectrophotometer, it is practically difficult to install a ROM in which the table of equation (2) created by actually measuring K is stored in each device. Prepare a ROM in which you have created and filled in a 0-formula table for the values, and install it in each spectrophotometer.A calibration test is performed on each spectrophotometer at the factory before shipment, and the data is recorded in the ROM in advance. The optimum table is selected from several tables, and when the spectrophotometer is used, the amount of rotation of the drive motor is converted into a wavelength value using the table.

(Problem to be Solved by the Invention) As described above, in a spectrophotometer in which a dispersive element is directly rotated by a motor via a deceleration mechanism, the rotation amount of the motor is converted into a wavelength value using a conversion table. In this case, the conversion table must be different for each spectrophotometer due to the manufacturing precision of the spectrometer, but in reality, the most suitable table is selected from several tables prepared in advance through a calibration test. The selected data will be used for subsequent measurements. For this reason, it is recommended to prepare tables in advance (the tables may vary slightly each time).Although it is desirable to prepare a large number of tables, the number of tables that can be prepared in advance is limited due to the capacity of the ROM. For spectrophotometers, there is no optimal table, and the best value is the intermediate value between the two values obtained from one table and the other. There may be cases where a relationship does not match any of the tables prepared in advance.However, conventionally there has been no easy way to deal with such cases.

Therefore, the present invention aims to provide a spectrophotometer that can deal with the above-mentioned problems without preparing a large number of conversion tables in advance.

(Means for solving the problem) A table for converting the amount of rotation of the motor that drives the dispersive element into a wavelength value is written in the ROM, and in order to obtain the correct wavelength value from the amount of rotation of the drive motor in a calibration test. A correction coefficient to be multiplied by the value drawn from the table in the ROM is determined, and this correction coefficient is stored in the memory of the spectrophotometer control device. i! , Correct the table in the ROM using the coefficients stored in the memory above,
A conversion table suitable for the spectrophotometer was created and stored in the RAM, and the wavelength was determined using the table from now on.

(Operation) The relationship between the rotation angle θ of the dispersive element and the wavelength λ can generally be expressed in the form λ=Kf(θ)=Kf(px)−(3), where X is the amount of rotation of the drive motor. θ becomes sin θ in the case of a diffraction grating. Here, the manufacturing errors of the spectrometer are summarized in the coefficient K, so prepare in advance in the ROM a table with appropriate values in equation (3) as a conversion table between the motor rotation amount X and the wavelength λ. Keep it
If the wavelength of the known wavelength light is determined based on the above table in the calibration test, the correction coefficient α to be multiplied by the wavelength determined from the conversion table in the ROM is determined. If this α is stored in memory, during actual measurement, the wavelength value corresponding to each X value drawn from the table in the ROM can be multiplied by α, and the result can be written in the RAM to create a correct conversion table for the spectrophotometer. can be generated in RAM. Therefore, from now on, by converting the amount of rotation of the drive motor into a wavelength value using this table in the RAM, the correct wavelength value can be determined.

(Embodiment) FIG. 1 shows a spectrometer used in a spectrophotometer according to an embodiment of the present invention, and FIG. 2 shows the overall configuration of the spectrophotometer. In FIG. 1, G is a plane diffraction grating, A is the rotation axis of the diffraction grating, and this rotation axis is the output axis of the speed reduction mechanism B. P is a pulse motor whose rotation is decelerated and transmitted to its output shaft A via a deceleration mechanism B.

Sl is the entrance slit of the spectrometer, S2 is the exit slit,
Ml converts the light incident from Sl into a parallel beam and converts it into a diffraction grating G.
M2 is a camera mirror that focuses the parallel light beam diffracted by the diffraction grating G onto the exit slit S2. . The direction of the diffraction grating in which the center normal of the diffraction grating coincides with the bisector of its own weight is the reference position of the diffraction grating G, and the rotation angle θ of the diffraction grating is measured from this reference position.

In FIG. 2, MC is the spectrometer shown in FIG. 1,
Ll and L2 are internal light sources built into the spectrophotometer, Ll is a deuterium lamp for short wavelength measurement, and L2 is a tungsten lamp for long wavelength measurement. Both light sources are connected to the switching mirror m1.
Depending on the input and output of the light, either light is made to enter the spectrometer MC. C is a sample chamber through which the light beam emitted from the spectrometer MC passes, and a sample can be set within the optical path of the light beam emitted from the spectrometer.

D is a photodetector that receives the spectrometer output light that has passed through the sample chamber C, and the output signal of the detector is amplified by an amplification section Ap and taken in as a control value ftK via an interface If. The control device includes a central processing unit CPU, an operating program,
ROM containing conversion tables, etc., non-volatile memory EEFRO
It is comprised of M, RAM, etc., and controls the entire device and performs data processing on photometric data taken in via If. CRT
Reference numeral F indicates a display section for displaying analysis results, etc., and F indicates an operation section through which the operator inputs various data to the control device and gives instructions regarding operations.

The above ROM contains the motor P designed for the above spectrophotometer.
The conversion table shown by the above equation 0 with the amount of rotation X is filled in. A configuration test of the spectrophotometer described above is performed as follows. This configuration test utilizes the spectrophotometer internal light source L1. . Ll is a deuterium lamp whose emitted light has wavelength characteristics as shown in FIG. 3, and 656. There is a sharp peak at lnm, and this peak is used for calibration. First, when the diffraction grating G is rotated in the direction of wavelength O, the 0th order diffracted light is detected at the position of wavelength O, so a peak search of the output of the photodetector is performed near wavelength O, and the peak center is detected. The direction of the diffraction grating G when the rotation is made is taken as a reference position, and the amount of rotation of the pulse motor P from that position is taken as X in the above equation 0. X
is the count value of the drive pulses supplied to the pulse motor P, and starts counting the drive pulses when the diffraction grating G is at the reference position. The supply of this driving pulse and the pulse count are C
PU will do it. When the diffraction grating G is driven from the reference position to the long wavelength side and the amount of rotation of the pulse motor P is counted, 656. An emission line of 1 nm is incident on the photodetector. Therefore, a beak search is performed for this 656° lnm light, and when the peak center is detected, the rotation amount X of the pulse motor P at that time is 656. It corresponds to a wavelength of lnm.

On the other hand, when the wavelength value is determined from the value of X using a conversion table stored in the ROM, it is generally a value λ' different from 656° lnm. Therefore, by multiplying the wavelength λ° found from this conversion table by the correction coefficient α=656.1/λ′, the correct wavelength value for this spectrophotometer can be obtained. This correction coefficient α is written into the non-volatile memory EEPROM to complete the calibration test.

Next, the operation of the above-mentioned spectrophotometer in actual use will be explained.

The conversion value for each X value is read from the conversion table in the ROM, multiplied by a correction coefficient α stored in the non-volatile memory EEPROM, and written to the RAM in association with the X value. A conversion table between the driving amount X of the pulse motor P in this spectrophotometer and the wavelength λ is formed. During actual measurement, the wavelength is determined from the amount of rotation of the pulse motor P using this conversion table.

In the above-described embodiment, the bright line of the internal light source of the spectrophotometer is used for the calibration test, but in this way, the user of the spectrophotometer can also perform the calibration test in a timely manner.

However, it goes without saying that the calibration test itself may be performed using an external light source. Further, although the above-described embodiment uses only one bright line light for the calibration test, the calibration test may be performed using bright lines of several wavelengths to determine the correction coefficient for each wavelength range. Furthermore, in the above embodiment, a designed conversion table is written in the ROM and is multiplied by a correction coefficient during actual use, but the table in the ROM simply contains p
Using the conversion table of tarn for
Even if it is stored in the OM, the reference position of the diffraction grating is detected by detecting the peak center of the 0th order diffracted light in the above embodiment, but if the reference position of the diffraction grating is It is also possible to set the bottle upright and detect this bottle at a specific position by charging or mechanical means, so that when the bottle is detected, the diffraction grating becomes the reference position.

(Effects of the Invention) According to the present invention, regardless of the existence of manufacturing errors in each spectrophotometer, any spectrophotometer can use a conversion table between the dispersive element rotation amount and wavelength that is suitable for each spectrophotometer. Moreover, a highly accurate spectrophotometer can be obtained without requiring a particularly large capacity ROM.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a spectrometer used in a spectrophotometer according to an embodiment of the present invention, FIG. 2 is a block diagram showing the overall configuration of the spectrophotometer according to the embodiment, and FIG. The spectral energy characteristic graph of the hydrogen lamp, FIG. 4, is a diagram illustrating the relationship between the light emission angle and the wavelength of the light of the diffraction grating. G... Diffraction grating, A... Rotation axis of diffraction grating, B...
・Deceleration mechanism, P...Pulse motor, Ml...Collimator mirror, M2...Camera mirror, Sl...Entrance slit, S2...Exit slit, Ll, L2...Light source, M
C... Spectrometer, C... Sample chamber, D... Photodetector,
K...Control device, EEFROM...Nonvolatile memory. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] A table for converting the amount of rotation of the motor that drives the dispersive element into a wavelength value is written in the ROM, and in order to obtain the correct wavelength value from the amount of rotation of the drive motor during a calibration test, the table in the ROM is retrieved. A correction coefficient to be multiplied by the value is determined, and this correction coefficient is stored in the memory of the spectrophotometer control device. During actual use, the table in the ROM is corrected by the coefficient stored in the memory. A spectrophotometer, characterized in that a conversion table suitable for the spectrophotometer is created, stored in a RAM, and the wavelength is determined using the table.