GB2135770A - Spectrophotometer - Google Patents

Abstract

A spectrometer of which the monochrometer can be automatically set to a peak wavelength set by the operator, comprises a light source 10, a cell 12 containing a sample, a monochrometer 11 with a dispersing element 14 driving it for scanning over a predetermined range of wavelengths, means 20 for detecting the peak output of a light measuring circuit 13, 16, 17, means 20, 21 for stopping the scanning when the peak output has been detected and means 18 for storing the peak output. <IMAGE>

Description

SPECIFICATION Spectrophotometer This invention relates to a spectrophotometer which quantitatively measures a sample by setting the monochromator to the peak wavelength in the spectrum of the sample and measuring the peak height of the spectrum.

With conventional spectrophotometers of the above-mentioned type, the operator manipulates a wavelength setting dial to change the wavelength of the light emerging from the monochromator adjacent the peak wavelength of the spectrum of a sample to be measured to search for and recognize the peak wavelength and adjust the wavelength of the light from the monochromator accurately to the peak wavelength, and then the intended quantitative measurement of the sample is conducted. The wavelength setting operation is troublesome and time-consuming.

Accordingly, the primary object of the invention is to simplify the wavelength setting operation in a spectrophotometer of the above-mentioned type.

SUMMARY OF THE INVENTION In accordance with the invention, when an operator sets the monochromator to the peak wavelength in the spectrum of a sample to be measured, the spectrophotometer itself automatically operates to scan a predetermined wavelength range extending at the opposite sides of the set wavelength so as to search for a peak in the spectrum and stop at the peak position detected thereby to automatically and accurately set the wavelength of the light to be measured to the peak wavelength of the spectrum of the sample to be measured.

In spectrophotometers, the wavelength indicated on the wavelength indicator ganged with the wavelength driving mechanism of the monochromator must coincide with the wavelength of the light emerging from the exit slit of the monochromator. Practically, however, there sometimes is a more or less difference between the two wavelengths.

In some cases, the peak wavelength of the spectrum of a substance in a solvent is slightly displaced from that of the same substance in a solvent of a different polarity.

Therefore, for quantitative measurement of a sample at the peak wavelength of the spectrum thereof it is necessary to search for and determine the peak wavelength, and in accordance with the present invention the above operation is automated with the only manual operation required being mere setting of a wavelength setting dial to the peak wavelength of the spectrum of a sample to be quantitatively determined. This not only alleviates the operative burden on the operator but also shortens the time required if a man operates the instrument to search for a peak in the spectrum of a sample under measurement while looking at the measured output.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a block diagram of one embodiment of the invention; and Figure 2 is a flowchart showing the operation of the apparatus of Fig. 1.

DESCRIPTION OF THE ILLUSTRATED EM BODIMENT One embodiment of the invention will be explained with reference to Fig. 1. The spectrophotometer comprises a light source 10, a monochromator 11, a sample cell 1 2 and a photo-detector 1 3. The monochromator 11 includes a dispersing element such as a diffraction grating 14 which disperses the light from the source into a series of wavelengths.

A wave-length driving device 1 5 drives the grating 14 so that a selected one of the wavelengths is taken out of the monochromator 11. The sample cell 1 2 contains a sample be analyzed. The monochromatic light passed through the sample is detected by the photodetector 13, which produces an electrical output in accordance with the intensity of the detected light.

The output from the photodetector 1 3 is amplified by an amplifier 1 6 and applied to an A-D converter 1 7 so as to be converted to a digital signal, which is written into a random access memory (RAM) 1 8.

A read only memory (ROM) 1 9 stores a program for detection of a peak wavelength of the sample under measurement. A micro-processor 20 controls the wavelength driving device 1 5 of the monochromator 11 through an input output port 21. The necessary data are entered into the microprocessor through a keyboard 22. The results of a measurement are printed out by a printer 23. A bus line 24 connects all these component elements.

The instrument of the invention is operated in the following manner. A sample to be quantitatively measured is put into the cell 1 2 and the known peak wavelength A of the spectrum of the sample is entered through the keyboard 22, and the measurement is started.

In accordance with the program stored in the ROM 1 9 the microprocessor 20 causes the wavelength driving device 1 5 to drive the grating 14 to a wavelength position of h that is, a predetermined wavelength width AA before the designated wavelength h previously entered and from that position to the position of A + AA for wavelength scanning.

During the scanning the microprocessor 20 takes in the output from the photodetector 1 3 through the A-D converter 1 7 and the input output port 21 for detection of a peak value of the photodetector output. When a peak has been detected, the grating 14 is stopped at the wavelength position, and the output of the photodetector 1 3 at that time as well as the wavelength designated by the operator are printed out by the printer 23 and/or stored in the RAM 1 8,-whereupon the measurement of the sample has been completed.

When a number of samples of the same substance to be measured have substantially the same peak wavelength, the above-mentioned peak detecting operation is conducted only on the first sample and may be omitted on the remaining samples if the instruction to continue the operation is given to the microprocessor 20 through the keyboard 22.

As previously mentioned, if a plurality of samples of the same substance have slightly different peak wavelengths due to the different polarities of the solvents for the samples or other causes, it is necessary to detect the peak wavelength of each sample to be measured. In this case this invention is particularly useful, and the detected peak wavelength as well as the standard peak wavelength set by the operator are stored in the RAM 1 8 and/or printed out by the printer 23 as one of the data obtained from each sample.

For the operation of detecting the peak wavelength any suitable program may be employed such as described in the flow-chart of Fig. 2.

When the program is started, initialization takes place, in which the RAM 1 8 is cleared and the first address At in a data area for detection of the peak wavelength is designated. Then, with the known peak wavelength A of the sample to be measured having been set by the operator beforehand, the grating is driven to the wavelength position of A - AA where hA is a small value as compared with A.

Then the stepping motor of the wavelength driving device 1 5 is driven by one pulse and the output B1 of the photodetector 1 3 is stored in the designated first address A, of the RAM 1 8. Then the data B0 (which is O at first) stored in the address Ao in the RAM, which is equal-to the designated address A, from which 1 is substracted, is read out, and the data B0 is substracted from the data B, to check whether or not B, -- B, > O. If B1 - B0 > O, 1 is added to the designated address A, and the operation is returned to the point X and proceeds downward.In this case the stepping motor is rotated another step to drive the wavelength and the output B2 of the photodetector is stored in the next address A2, so that the data B, in the previous address A, is substracted from the data B2 in the address A2 to check if B2 - B1 > 0.

As the operation is repeated in the closed loop in the above manner, the stepping motor is rotated step by step to drive the wavelength until the result of subtraction of B,, from Bn becomes equal to or smaller than zero, that is, B, -- B,,O, whereupon the position of the grating is recognized as the peak wavelength position, so that the wavelength is calculated from the designated address An (or A"-') at that time and then stored in a data area in the RAM 18.

Then the measured output of the photodetector 1 3 is stored in a data area in the RAM 18, whereupon the measurement of the sample is completed. Then it is checked whether or not the continuation key is pushed. If it is not, the operation ends. If the key has been pushed, upon issuance of the instruction to start, the operation is returned to the point Y for measurement of a new sample.

Claims (6)

1. A spectrophotometer comprising: a light source; a monochromator including a dispersing element; a cell containing a sample to be measured, a light measuring circuit; means for driving said dispersing element for wavelength scanning over a predetermined range of wavelengths including a designated wavelength, means for detecting a peak in the output of said light measuring circuit, means for stopping the scanning of said driving means when a peak in said output has been detected by said detecting means thereby to set said designated wavelength to the peak wavelength, and means for storing said peak output of said light measuring circuit.

2. The spectrophotometer of claim 1, further including means for recording said peak output of said light measuring circuit.

3. The spectrophotometer of claim 1 or 2, wherein said peak detecting means comprises a RAM including a plurality of addresses for storing the output of said light measuring circuit, a ROM for storing a predetermined program for detecting the peak wavelength, and a microprocessor for controlling reading of data out of or writing data into said addresses of said RAM and conducting necessary operations based on the data stored in said addresses in accordance with said predetermined program.

4. The spectrophotometer of claim 2 or 3, wherein said microprocessor also controls the operation of said recording means.

5. A spectrophotometer as claimed in claim 1 and as herein described and/or as illustrated in the accompanying drawings.

6. Each and every novel embodiment herein disclosed either separately or in combination.