JPS61132827A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To correct a variation of a base line, and to always keep an optimum signal level by stopping an AGC by fixing a storage sensitivity of a means for executing the AGC except the time of a measurement, and storing a sensitivity of a photometric system at the time of a measurement. CONSTITUTION:In a photometric system consisting of a phtodetector (PM) of a single beam system, a preamplifier (PA), a detector sensitivity controlling circuit (GC) and a signal processing part (SP), an output of the PA is compared with a reference value, a sensitivity of the PM is controlled, and the GC is operated so that an output of the PA keeps a level of an absorbance '0'. Also, a controlling circuit (CT) for executing an AGC is constituted so that an output of the GC is fixed to a level of immediately before a measurement is started, through a sensitivity storing circuit of its inside. In this way, an influence of a luminous intensity variation of the absorbance is corrected by correcting the sensitivity so that a base line is not varied at the time of non-measurement, and the sensitivity can be read directly on recording.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a single beam type spectrophotometer. - Conventional technology Spectrophotometers are broadly classified into double beam type and single beam type. The double beam method can automatically correct the influence of the wavelength characteristics of the light source, the wavelength characteristics of the temporal change 2 spectrophotometer itself, and the spectral transmittance of the sample container, solvent, etc., but the device configuration is complicated. Although the above-mentioned correction cannot be made automatically with the single beam method, it has become possible to use memory and processing devices at low cost in recent years, so it is possible to make corrections by storing the photometric data of the reference sample. Since it has become possible to compensate for the influence of the spectral characteristics of the spectrophotometer itself, the sample container, the solvent, etc., it has become a major advantage that the device configuration is simpler than the double beam method.

However, with the single beam method, even if memory is used, it is not possible to compensate for temporal fluctuations in the light source, so the baseline changes during measurement. Therefore, unless the baseline is changed appropriately during measurement, the measurement output will overscale. However, there is a problem in that the signal level is out of the optimal range for the signal processing circuit.

C. Problems to be Solved by the Invention The present invention attempts to use a single beam method so that baseline fluctuation does not occur and the optimum signal level is always maintained for the signal processing section.

21 Means for Solving Problems The spectrophotometer of the present invention is a single-beam type, and performs AGC (automatic gain control) at all times except when measuring a sample to correct baseline fluctuations, while constantly storing the sensitivity of the measurement system. A means is provided to fix this sensitivity memory and use AGC when measuring a sample.
The operation was stopped.

E. Example The figure shows an example of the present invention. This example shows the case where atomic absorption spectrometry is performed. HCL is the hollow can-tramp light source, and F is the flame of the sample atomization section, which mixes the sample into the fuel gas during sample measurement. MC is a spectrometer, PM is a photomultiplier tube as a photodetecting element, and FA is a preamplifier.
The output is input to the signal processing section sp. GC is a detector sensitivity control circuit that compares the output of the preamplifier FA with a reference value, adjusts the sensitivity of the photodetector PM based on the difference between the two, and operates so that the output of the preamplifier FA is maintained at the reference value. There is. In other words, A G and C are performed in a feedback loop of PM, FA, and GC.

The above reference value corresponds to absorbance of 0, and due to the action of AGC, absorbance is 0 (in case of transmittance measurement, transmittance is 100%)
The signal processing section sp, whose level is kept constant, converts the output of the preamplifier FA into an absorbance value, and outputs this to the display section DP. The display section DP displays the absorbance numerically and records it on the recording paper.

The configuration from the photodetector/M to the signal processing section is the photometric system of the spectrophotometer.

The control circuit CT normally operates the above-mentioned AGC, but when measuring a sample, the output of the detector sensitivity control circuit GC is fixed to the value immediately before starting the sample measurement.

FIG. 2 shows the inside of the detector sensitivity control circuit OC.

FXA is an error amplifier, and normally the switch SWI is in contact with the contact a side, the output V of the preamplifier PA is applied to the inverting terminal through the resistor R1, and the non-inverting terminal is connected to the switch Sw2.
It is connected to the ground level through contact a'. In other words, this ground level is the reference level for comparison of comparator KA. The output of KA is converted into a direct current negative high voltage by a DC/DC converter DC and applied to the dynode of the photodetector PM. The output of the DC/DC converter DC is divided by resistors R3 and R4 and input to the sensitivity storage circuit SM. The sensitivity memory circuit SM includes a memory capacitor C, a memory fixing switch Sw3, and a buffer amplifier BA. Normally, the switch Sw3 is closed, and the charging voltage of the capacitor C, ie, the stored content changes in accordance with the output change of the iDc/DC converter DC. The control circuit CT controls the switches SWI to Sw3, and upon receiving a sample measurement command, switches the switches aw1. switch to the contact side, switch 8w2 to the contact b' side, and open the switch Sw3. Therefore, the memory contents of the sensitivity memory circuit SM are fixed at the level immediately before 8w3 was opened. The output of the DC/DC converter DC divided by resistors R3 and R4 is applied to the non-inverting terminal of the error amplifier EA through the switch SWI, and the above-mentioned fixed memory is applied to the non-inverting terminal of the switch Sw2. The output of the DC/DC converter is maintained at the output immediately before switching to the sample measurement state.

Of course, it is possible to enter the command for sample measurement into the control circuit manually each time the sample is changed, but it is also possible to give the program for automatic measurement of a large number of samples to the control circuit CT, and then input it to the control circuit each time the sample is changed. In addition to automatically supplying the sample, it is also possible to switch the switches Swl to 13w3 to the sample measurement mode immediately before introducing a new sample, then introduce the sample, and return the switches SWI to Sw3 to the normal state after the measurement is completed. can.

Figure 3A shows an example of absorption analysis recorded by a conventional single-beam spectrophotometer.In this example, the luminous intensity of the light source decreases over time, and the baseline Z! (absorbance 0) is gradually increasing.

During sample measurement between times t1 and t2 and between t3 and t4, h and h/ are expressed as absorbance, and the apparent absorbance increases as the luminous intensity of the light source decreases. Figure 3B is a record of absorbance measurement using the spectrophotometer of the present invention, which is the baseline! is kept horizontal when not measuring, and the sample measurement period t
From 1 to t2 and from t3 to t4, the sensitivity of the photometric system is fixed,
The absorbance is given by h and h/, respectively. Although the luminous intensity of the light source is decreasing over time, the photometric system is corrected to prevent the baseline from changing when not measuring, so the recorded absorbance and h/ are corrected for the effects of luminous intensity changes. and recorded on the same scale,
Absorbance can be directly traced from the record. In the conventional example shown in Fig. 3A, there is a risk that the upper limit of recording may exceed the scale, so in automatic measurements, the sensitivity tends to be set low to avoid wasting measurements. Since there is no need to worry about overshooting, the sensitivity is controlled so that the signal processing unit SP operates within the best linear range according to the expected absorbance of the sample, regardless of fluctuations in the light source.
Taking advantage of the simple structure of the single beam system,
The effect of the double beam method can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram of a gain control system in the same embodiment, and FIG. 3A
4B is a graph illustrating a measurement record according to the conventional example, and 4B is a graph illustrating a measurement record according to the present invention.

Claims (1)

[Claims] The single beam system is equipped with an automatic gain control means for the photometry system, a means for storing the gain of the photometry system, and the above automatic gain control means is operated except when measuring a sample, and when measuring a sample, it is equipped with a means for storing the gain of the photometry system. A spectrophotometer comprising control means for holding the gain in the storage means and fixing the gain of the photometric system to the fixed gain.