JPH05215605A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To prevent the distortion of spectrum by taking in photometric values being sampled with an accurate wavelength at a take-in position while executing wavelength driving and signal processing through a common CPU. CONSTITUTION:A motor drive section 4 rotates the step motor in a spectrometer 2 at a constant pulse rate and a signal processing section 8 subjects a photometric signal delivered from the spectrometer 2 to A/D conversion through an A/D converter 6 at a constant sampling period T2 while furthermore subjects the photometric signal to a predetermined signal processing to produce a photometric value which is updated at the sampling period T2. A control section 10 sets the wavelength feed period T1 between wavelengths, for taking in photometric values as a data from the signal processing section 8, integer times of the sampling period T2 and matches the starting points of time of the periods T1 and T2 thus controlling the motor drive section 4 and the signal processing section 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrophotometer used for measuring the absorbance of various samples, and more particularly to a spectrophotometer which takes in a photometric value as a digital signal.

[0002]

2. Description of the Related Art In a digitized spectrophotometer, a diffraction grating is rotated by a stepping motor to perform wavelength scanning, and a photometric signal by a spectroscope is sampled and digitized and taken in. Two methods of (B) are used. (A) The stepping motor is stopped every time the wavelength of the spectroscope reaches the position for taking in the photometric value, the photometric signal is sampled a plurality of times (the number of times depends on the wavelength scanning speed), the average is obtained, and at that wavelength The photometric value of. (B) A dedicated CPU performs signal processing until the photometric value is sampled and converted into a digital signal and signal processing (response processing) for noise reduction is performed, and the wavelength from the wavelength at which the photometric value is captured as data to the next wavelength The photometric value is updated at a cycle sufficiently faster than the wavelength sending time up to.

[0003]

In the method (A), since the photometric value is sampled at each wavelength position, there is no deviation between the displayed wavelength and the wavelength at the actual sampling position, but the response The value will depend on the wavelength scanning speed. Further, when the stepping motor is temporarily stopped at the position where the data is sampled, if the wavelength scanning is performed at a high speed, the motor is out of synchronization, so that there is a drawback that the high speed wavelength scanning cannot be performed. The method (B) is a preferable method, but the CPU for signal processing and the other CPU including the driving of the stepping motor must be separately provided, resulting in a large device configuration and a low-cost general-purpose spectroscopy. Not suitable for photometric applications.

Therefore, in order to be applicable to a low-cost spectrophotometer, the wavelength drive and the signal processing are common CPUs.
Need to be run in. In order to be able to set the response of the signal independently of the wavelength scanning speed, it is necessary to sample the signal at a constant sampling period and perform digital signal processing. Further, a stepping motor is generally used as the actuator for driving the spectroscope, but in order to rotate the stepping motor at a high speed without step-out, it is necessary to rotate at a constant pulse rate.

As a result, the wavelength driving and the signal processing are common to the C
In order to be executed by the PU, the CPU needs to process the following three tasks simultaneously. (1) The stepping motor is rotated at a constant pulse rate in association with the wavelength value, and each time the wavelength at which the photometric value is captured is reached, the point is notified to (3) described later. (2) The photometric signal from the detector is sampled at a constant sampling period, signal processing is performed, and the photometric value is updated. (3) The photometric value is taken in according to the instruction from (1), and the spectrum and the photometric value are displayed.

Among these tasks, (1) the cycle for taking in the photometric value and (2) the processing for sampling the photometric signal and updating the photometric value have different cycles, but both are performed at a constant cycle. Therefore, if these two cycles are performed asynchronously, the photometric value sampled at a certain wavelength may not be the one sampled at that wavelength position, resulting in distortion of the spectrum. Become. For example, as shown in FIG. 5, if the period for taking in the photometric value is T ₁ and the period for sampling and updating the photometric value is T ₂ , then Td ₁ , Td ₂ , at each photometric value taking wavelength position. … There is a time lag. As a result, the spectrum is distorted as shown in FIG.

According to the present invention, the wavelength driving and the signal processing are common to each other.
The object is to prevent the distortion of the spectrum by causing the photometric value sampled at the wavelength to be correctly captured at the photometric value capturing position while being executed by the PU.

[0008]

FIG. 1 shows the present invention. The spectrophotometer of the present invention comprises a spectroscope 2 having a diffraction grating rotated by a stepping motor, a motor drive unit 4 for rotating the stepping motor of the spectroscope 3 at a constant pulse rate, and photometry of the spectroscope 2. Signal to A / D converter 6
After that, the signal processing unit 8 performs A / D conversion at a constant sampling period T ₂ , performs predetermined signal processing, and updates as a photometric value every period T ₂ , and a photometric value is fetched from the signal processing unit 8 as data. wavelength sending period T ₁ is set to an integral multiple of the sampling period T _2, and the motor drive unit 4 and the signal processing unit 8 to the beginning at the same time at the start and the period T ₂ of the cycle T ₁ of the inter-wavelength for And a control unit 10 for controlling.

[0009]

When the period T _{1 is set} to an integral multiple of the period T ₂ and started at the same time, as shown in FIG. 2, when the wavelength advances to the wavelength position for taking in the next photometric value, the wavelength position is always changed. The photometric signal is sampled in and the photometric value is updated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The motor drive unit 4, the signal processing unit 8 and the control unit 10 shown in FIG. 1 are realized by a common CPU.

The operation of one embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 shows the entire operation. The parameters of the device are set according to the measurement conditions. The parameters include the response, the measurement wavelength range, the wavelength scanning speed, the period T ₁ for capturing the photometric value, and the like. Once the parameters are set,
The timers of the motor driving timing generation period and the photometric value sampling period T ₂ are activated, and the program branches to each program activated by the interruption of these timers.
Each program is shown in FIG.

FIG. 4A is a program for driving the stepping motor of the spectroscope. 1 stepper motor
If the wavelength is step-rotated and the wavelength is the next wavelength position for capturing the photometric value, a data acquisition command is issued, otherwise, the data acquisition command is not issued, and the stepping motor is rotated again by one step after a fixed time. repeat. (B) is a signal processing program. Period T ₂
The photometric value is sampled for each A / D conversion, and signal processing (response processing) such as moving average for noise reduction is performed to update the photometric value. (C) is the main program. When the next wavelength position for capturing the photometric value is reached and a data capture command is issued, the signal processing is performed and the updated photometric value is captured and displayed.

[0013]

According to the present invention, the wavelength sending cycle T ₁ between wavelengths for capturing the photometric value as data is set to an integral multiple of the sampling cycle T ₂ , and the start time of the cycle T ₁ and the cycle T ₁ are set.
_Since the start times of ₂ are coincident with each other, the photometric value sampled at that wavelength can be correctly captured at the photometric value capturing position, and high-speed wavelength scanning can be performed without spectrum distortion. The response value can be set independently of the wavelength scanning speed. Since the wavelength drive and the signal processing can be realized by a single CPU, a simple control system is sufficient and it is advantageous to apply to a low cost device.

[Brief description of drawings]

FIG. 1 is a block diagram showing the present invention.

FIG. 2 is a timing chart showing the operation of the present invention.

FIG. 3 is a flowchart showing the overall operation of one embodiment.

FIG. 4 is a flow chart showing the operation of each part of the embodiment, (A) showing a motor drive program, (B) showing a signal processing program, and (C) showing a main program.

FIG. 5 is a timing chart showing a general operation when wavelength driving and signal processing are executed by a common CPU.

FIG. 6 is a diagram showing an example of a spectrum obtained by the operation of FIG.

[Explanation of symbols]

 2 spectroscope 4 motor drive unit 6 A / D converter 8 signal processing unit 10 control unit

Claims (1)

[Claims] 1. A spectroscope having a diffraction grating that is rotated by a stepping motor, and a motor drive unit that rotates the stepping motor at a constant pulse rate.
A / meter the photometric signal of the spectroscope at a constant sampling period T _2.
The signal processing unit that performs D conversion, performs predetermined signal processing, and updates as a photometric value at each cycle T ₂ thereof, and the wavelength sending cycle T ₁ between wavelengths for taking in the photometric value as data from the signal processing unit is the T _It is set to an integral multiple of ₂ and includes a control unit for controlling the motor driving unit and the signal processing unit at the same time when the start time of the cycle T _{1 and} the start time of the cycle T ₂ are provided. Photometer.