JPH0684909B2 - Spectrophotometer - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a spectrophotometer using an element having no self-multiplication function such as a photodiode as a photodetector,
The present invention relates to a gain switching mechanism of an amplifier circuit.

B. 2. Description of the Related Art Photodetectors used in spectrophotometers need to have an amplifying circuit such as a photomultiplier tube and an amplifying circuit that does not have an amplifying function. It can be roughly divided into things. On the other hand, in the spectrophotometer, the energy of the light transmitted through the spectroscope changes greatly depending on the wavelength due to the spectral characteristics of the light source and the spectral transmission characteristics of the spectroscope, and a signal of a substantially constant magnitude is generated in response to this changing energy. In the spectrophotometer using a photomultiplier tube, the sensitivity of the detection element itself is changed by the dynode feedback method, but a detection element that does not have an amplification function such as a photodiode is used. However, since it is difficult to realize an amplifier circuit which can control the gain in a concatenated manner, it is possible to switch the gain of the light quantity adjusting means using a servo mechanism or the gain of the amplifier to several stages so that the amplifier is discrete. The method of switching the sensitivity of the photometric system is used.
The present invention relates to the latter method, but in the conventional spectrophotometer of this method, if the gain is switched during recording of the spectrum, a shock noise appears on the spectrum, so that the wavelength scanning is once performed at the time of switching. Had to be stopped and time wasted recording the spectrum.

C. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention uses an element that does not have an amplifying function itself as a photodetection element and requires an amplifying circuit, and the gain of the amplifying circuit is switched to a plurality of stages so that the gain is substantially constant in the measurement wavelength range. In a spectrophotometer that can obtain a constant signal, when performing gain switching during spectrum recording as described above, it was necessary to temporarily stop wavelength scanning, whereas the wavelength stop period during spectrum recording It aims to minimize time and measure the time economy.

D. Means for achieving the object When scanning a wide wavelength range with a spectrophotometer, filters for cutting higher-order light of a diffraction grating are sequentially replaced, so in the present invention, the photometry system is linked with this filter replacement during the filter replacement. The number of times the wavelength scanning is stopped is reduced by switching the gain of.

E. Action In FIG. 2, the horizontal axis represents wavelength and the vertical axis represents output of the photometric system, showing an example of spectrum recording of a blank sample. In this figure, f1, f2, etc. are the wavelengths at which the high-order optical cut filter was exchanged, and a step appeared in the spectrum recording at the exchanged location. This figure is a record under a constant gain set so that the highest point of the spectrum is within the range where the amplifier is not saturated, and the signal strength is extremely low near both ends of the spectrum. Conventionally, the sensitivity switching level is set to 1, 12 for example, and the gain is switched at this level, so the spectrum scanning is stopped at t1, t2, etc. in addition to f1, f2, etc. I needed it.

In the present invention, when the filter is exchanged, the necessity of the gain switching is examined, and the gain is switched by using the filter exchange. Therefore, the spectrum recording corresponding to FIG. 2 is as shown in FIG. The signal level labeled V in this figure provides a level for gain switching. When the signal level is in the process of rising along with the wavelength scanning, when the filter is exchanged, and the signal level exceeds V, the gain is cut down,
When the signal level is in the process of falling along with the wavelength scanning, the filter is exchanged and the gain is rounded up if the signal level is below V at that time. As a result, the spectrum recording becomes as shown in the figure, and the wavelength scanning is stopped only at the filter exchange points such as f1 and f2, and the extra stop points t1 and t2 as shown in FIG. 2 are eliminated. In this description, for the sake of simplification, rounding up or rounding down the gain is determined based on a signal change tendency at a single level, but since the spectrum generally shows a plurality of changes, the rounding up level of the gain is rounded down as in the embodiment described later. It is better to set separately.

F. Embodiment FIG. 1 shows an embodiment of the present invention. Reference numeral 1 is a light source, and 2 is a high-order optical cut filter in which plural kinds are arranged in the circumferential direction, and the filters are exchanged by rotation. 3 is a spectroscope, 4 is a sector mirror that splits the light emitted from the spectroscope into two light beams, 5 is a reference sample, 6 is a sample to be measured, 7 is a photodetector,
Reference numeral 8 is a preamplifier whose gain is switched. Reference numeral 9 denotes a gain switching resistor group of the briamplifier 8, which switches the gain by changing the combination of resistors by a switch. Reference numeral 10 is a signal separation switch, which is an analog switch that operates by the rotation and rotation of the sector mirror 4, and uses the A / D converter 1 as the reference signal.
1, the sample signal to be measured is distributed to the A / D converter 12. A divider 13 divides the measured sample signal by the reference signal. Reference numeral 14 is a control unit for controlling filter exchange, gain switching and the like.

The gain switching operation of the control unit 14 is performed as follows. The control unit 14 controls the wavelength scanning of the spectroscope 3 to detect the wavelength, stops the wavelength scanning at a predetermined wavelength position, replaces the filter 2, and outputs the A / D converter 11 after replacing the filter. That is, the data (referred to as R) of the reference signal is read, and if R is below the lower limit level Vl of the gain switching, the gain is switched to the higher gain. If R is above the upper limit Vh of the gain switching, the gain is switched to the lower gain. Then, the wavelength scanning is restarted.

G. Effect According to the present invention, during spectrum recording, the gain switching of the photometric system is performed by utilizing the time of filter replacement.
The scan stop period is reduced, and the required measurement time is shortened.

[Brief description of drawings]

FIG. 1 is a block diagram of a spectrophotometer according to an embodiment of the present invention, FIG. 2 is a spectrum recording without gain switching, and FIG. 3 is a graph for explaining the operation of the present invention.

Claims (1)

[Claims] 1. A means for exchanging a high-order light cut filter in association with wavelength scanning of a spectroscope, and a gain of the photometric system depending on whether or not the output of the photometric system when the filter is exchanged exceeds a predetermined level. A spectrophotometer comprising means for determining whether or not to switch, and means for switching the gain of the photometric system according to the determination that the gain of the determining means should be switched when the filter is replaced.