JPH0660844B2 - Spectrophotometer - Google Patents

Description

The present invention relates to a spectrophotometer, and more particularly to a spectrophotometer of a type in which a dispersive element is rotated by a motor for wavelength scanning or wavelength setting.

(Prior Art) A sine bar mechanism has been conventionally used as a wavelength scanning mechanism of a spectrophotometer using a diffraction grating. This mechanism is a sine bar projecting from a diffraction grating axis by a nut moved by a feed screw. The bar is pushed, and there is an advantage that the rotation amount of the feed screw has a linear relationship with the wavelength, but it is difficult to feed the wavelength at a high speed because the feed index is used. With the recent spread of computer technology, the operation of converting the amount of rotation of a pulse motor into an arbitrary function value has become easier and faster, and even in spectrophotometers, the feed screw of the sine bar mechanism is also used. The advantage that the amount of rotation and the wavelength are in a linear relationship is weakened, the problem that high-speed wavelength transmission is difficult becomes problematic, and it is also structurally simple and inexpensive, so A spectrophotometer has come to be used in which an element is directly rotated through a reduction mechanism.

In the spectrophotometer of the type that directly rotates the spectroscopic element via the speed reduction mechanism, even when the diffraction grating is used as the dispersive element, the relationship between the amount of rotation of the motor and the wavelength is no longer linear, and when the diffraction grating is used as the dispersive element. , The relationship between the rotation angle θ of the diffraction grating from the reference position and the wavelength λ is defined as follows: d is the grating constant of the diffraction grating and n is the diffraction order. It is represented by. Here, the angle φ is half the angle formed by the incident light and the diffracted light on the diffraction grating G as shown in FIG. 4, and is 1 / one of the angle formed by the entrance and exit slits of the spectroscope with respect to the center of the diffraction grating.
It is 2. Since the relationship between the rotation angle of the diffraction grating and the wavelength is as shown in equation (1), in the spectrophotometer of the type that directly rotates the dispersive element via the reduction mechanism, the rotation amount x of the dispersive element drive motor is set to On the other hand, the rotation amount of the drive motor is converted into a wavelength value using a ROM in which a relational table of λ = Ksinpx, where θ = px (2) is entered. In the above formula (2), p is a constant determined by the speed reduction mechanism, but K includes the lattice constant of the diffraction grating and the amount related to the position of the optical element such as the entrance / exit slit of the spectroscope as shown in the formula (1). However, these include errors in the fabrication and assembly of the spectroscope, and even spectrophotometers made with the same design are slightly different for each device. However, in manufacturing a spectrophotometer, it is practically difficult to say that each device is equipped with a ROM that records the table of formula (2) created by actually measuring K. Regarding the values, prepare a ROM in which the table of equation (2) is created and filled in, install it in each spectrophotometer, and perform a calibration test for each spectrophotometer at the time of shipment from the factory, and store it in ROM beforehand. The optimum table is selected from the several recorded tables, and when the spectrophotometer is used, the rotation amount of the drive motor is converted into the wavelength value by the table.

(Problems to be Solved by the Invention) In the spectrophotometer of the type in which the dispersive element is directly rotated by the motor through the reduction mechanism, as described above, the rotation amount of the motor is converted into the wavelength value by using the conversion table. In that case, the conversion table must be different for each spectrophotometer depending on the working accuracy of the spectroscope, but from the several tables prepared in advance, the most suitable table is obtained by the calibration test. Is selected for use in subsequent measurements. For this reason, it is desirable to prepare a large number of tables so that the tables prepared in advance differ little by little, but the number of tables prepared in advance is limited due to the capacity of the ROM. There is no optimum table in the meter, and it means that the intermediate value of the two values obtained from one table and the other table is the best, and in some spectrophotometers, the rotation amount of the motor and the wavelength value are In some cases, the relationship does not match any of the tables prepared in advance. However, in the past, there was no simple method for dealing with such a case.

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

(Means for Solving the Problem) A conversion table creating function for converting the amount of rotation of the dispersive element drive motor into a wavelength value is provided, and a calibration operation mode can be designated. In the calibration mode, a bright line light of a known wavelength can be specified. Perform the detection operation, determine the count used for creating the conversion table from the rotation amount of the drive motor when the same bright line is detected and the known wavelength of the bright line, and create a conversion table using the coefficient. The spectrophotometer is provided with a control device for storing the rotation amount of the drive motor into a wavelength value according to the conversion table stored in the nonvolatile memory during the analysis operation.

(Operation) The relationship between the rotation angle θ of the diffraction grating and the wavelength λ is given by the above equation (2). Here, K varies from device to device due to variations in the positions of optical elements such as the lattice constant and slits.
Since the control device has a function of creating a table for converting the rotation amount x of the drive motor into a wavelength by the above equation (2), K
It is possible to create a table for converting the motor rotation amount x into a wavelength by actually determining the value of ω by the calibration operation. If you create this table one by one during the actual analysis, it will take time to calculate the table, but since the created table is saved in the non-volatile memory, the amount of rotation of the motor will be stored in the memory during the actual analysis. Can be immediately converted to wavelengths.

(Embodiment) FIG. 1 shows a spectroscope used in a spectrophotometer according to one embodiment of the present invention, and FIG. 2 shows the entire structure of the spectrophotometer. In FIG. 1, G is a plane diffraction grating, A is a rotation axis of the diffraction grating, and this rotation axis is the output shaft of the speed reduction mechanism B. P is a pulse motor, the rotation of which is reduced in speed and transmitted to the output shaft A through the speed reduction mechanism B. S
1 is an entrance slit of the spectroscope, S2 is an exit slit, and M
Reference numeral 1 denotes a collimator mirror that collimates the light beam incident from S1 and makes it enter the diffraction grating G, and M2 denotes a camera mirror that condenses the parallel light beam diffracted by the diffraction grating G on the exit slit S2. The bisecting angle becomes the angle φ in the equation (1). The direction of the diffraction grating where the center normal of the diffraction grating coincides with the bisector of the angle Ψ 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 spectroscope shown in FIG.
L1 and L2 are internal light sources with a built-in spectrophotometer, L1 is a deuterium lamp for short-wavelength region measurement, and L2 is a tungsten lamp for long-wavelength region measurement. These two light sources are switching mirrors m1.
Any light is made to enter the spectroscope MC by entering or exiting. In the sample chamber C, the light flux emitted from the spectroscope MC passes therethrough, and the sample can be set in the optical path of the light flux emitted from the spectroscope. D is a photodetector that receives the light emitted from the spectroscope that has passed through the sample chamber C. The output signal of the detector is amplified by the amplification unit Ap and is taken into the control device K via the interface If. The control unit K includes a central processing unit CPU, an operation program, a ROM in which a program and the like are written to create a conversion table, and a non-volatile memory EE.
It is composed of PROM, RAM, etc., and controls the entire apparatus and performs data processing on the photometric data fetched via If.
CRT is a display unit for displaying analysis results and the like, and F is an operation unit for an operator to input various data to the control device and to give instructions regarding operations.

The above-mentioned ROM has a motor P for designing the spectrophotometer.
The conversion table creating program for the rotation amount x and the wavelength, which is represented by the formula (2), is entered. The calibration test of the spectrophotometer described above is performed as follows. The spectrophotometer internal light source L1 is utilized for this calibration test. L1 is a deuterium lamp, and its radiated light has a wavelength characteristic as shown in FIG.
There are sharp peaks at 0 nm and 656.1 nm, and this peak is used for calibration. First, when the diffraction grating G is rotated in the direction of wavelength 0, the 0th-order diffracted light is detected at the position of wavelength 0. Therefore, the peak search of the output of the photodetector D is performed near the wavelength 0, and the peak center is detected. The direction of the diffraction grating G at this time is set as the reference position, and the rotation amount of the pulse motor P from that position is set as x in (2) above. x is a pulse motor P
With the count value of the drive pulse supplied to the, the counting of the drive pulse is started when the diffraction grating G is at the reference position. The CPU supplies the drive pulse and counts the pulse. When the diffraction grating G is driven from the above-mentioned reference position to the long wavelength side and the amount of rotation of the pulse motor P is counted, the
The bright line of 6.0 nm and then 656.1 nm is the photodetector D.
Incident on. Therefore, these 486.0 nm and 656.
When the peak search of 1 nm bright line light is performed and the peak center is detected, the rotation amount x of the pulse motor P at that time is 4
Corresponding wavelengths of 86.0 nm and 656.1 nm.
From the value of x and the wavelengths of the two bright lines stored in the ROM, K in the equation (2) can be determined. K is the average of the values obtained from the two bright line lights. After that, a conversion table is created by the conversion table creation program, and the nonvolatile memory EEPROM
Write to.

The conversion table creation program calculates the wavelength λ for the value of x for each step of the rotation amount of the pulse motor P, and as described above, the speed reduction mechanism B such that xp = θ, generally a diffraction grating drive. It is necessary to calculate the sine of px as shown in equation (2), where p is a constant determined by the mechanism, but in order to shorten the calculation time, the value of sinpx for some values of x is set in advance. It is calculated and stored in ROM, and the intermediate x value is sinp by an appropriate interpolation calculation.
x is calculated, and sin calculated in this way
The value of K described above is multiplied by px, and the value of x is written in the nonvolatile memory EEPROM together with each step.

Next, when an actual analysis is performed, the wavelength value corresponding to the rotation amount x of the pulse motor P from the reference position of the diffraction grating G may be extracted from the conversion table in the nonvolatile memory EEPROM.

Although the bright line of the internal light source of the spectrophotometer is used for the calibration test in the above-described embodiment, this allows the user of the spectrophotometer to perform the calibration test. However, it goes without saying that the calibration test itself may be performed using an external light source. Further, in the above-described embodiment, the calibration test uses only two bright line lights, and the K value uses the average of the K values obtained from the two bright line lights, but in theory, one bright line light beam is used. It is possible to calibrate by itself if a diffraction grating is used as the dispersive element. However, in reality, K in equation (2) above
The value of is also a function of wavelength due to variations in the lattice constant depending on the location on the lattice. Therefore, the value of K is obtained based on some emission line lights, and K is set as a function of x by the least square method or the like. If the conversion table is created in the form of K (x) sinpx, extremely accurate calibration can be performed.

Although the reference position of the diffraction grating is detected by detecting the peak center of the 0th-order diffracted light in the above-described embodiment, a pin is set on the rotation axis of the diffraction grating and this pin is detected photoelectrically or mechanically. Alternatively, the diffraction grating may be in the reference position when the pin is detected.

(Effects of the Invention) According to the present invention, regardless of the existence of a working error in each spectrophotometer, the conversion table of the dispersion element rotation amount and the wavelength suitable for each spectrophotometer is used. Therefore, a highly accurate spectrophotometer can be obtained without requiring a ROM having a particularly large capacity.

[Brief description of drawings]

FIG. 1 is a perspective view of a spectroscope used in a spectrophotometer according to an embodiment of the present invention, FIG. 2 is a block diagram showing the entire structure of the spectrophotometer of the embodiment, and FIG. 3 is a weight diagram used for a calibration test. A spectral energy characteristic graph of the hydrogen lamp, and FIG. 4 are diagrams for explaining the relationship between the incident and outgoing angles of light of the diffraction grating and the wavelength. G ... Diffraction grating, A ... Rotation axis of diffraction grating, B ... Reduction mechanism,
P ... Pulse motor, M1 ... Collimator mirror, M2 ... Camera mirror, S1 ... Entrance slit, S2 ... Exit slit, L1,
L2 ... Light source, MC ... Spectrometer, C ... Sample chamber, D ... Photodetector, K ... Control device.

Claims (1)

[Claims] 1. In a diffraction grating spectrophotometer of the type in which the rotation of a motor is directly converted into the rotation of a dispersive element without passing through a sine bar, p is a diffraction grating driving motor in which p is a constant determined by the driving mechanism of the diffraction grating. Is provided with a conversion table creating function for calculating λ by giving x by a basic expression λ = Ksinpx for converting the rotation amount x of the wavelength value λ, and the calibration operation mode can be designated. Of the drive motor and the known wavelength of the bright line when the same bright line is detected, the coefficient K used for creating the conversion table is determined, and the conversion table is calculated using the coefficient K. Is stored in a non-volatile memory and has a control device for converting the rotation amount of the drive motor into a wavelength value according to the conversion table in the memory during analysis operation.