JPH0668467B2 - Photometric device for emission spectroscopy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photometric device used for emission spectroscopic analysis such as high-frequency plasma emission.

(Prior Art) When a sample is caused to emit light by high-frequency induction plasma or the like and quantitative analysis of the elements contained in the sample is performed, the emission intensity of each element is different. It is necessary to set different measurement sensitivities. For example, in the device proposed in Japanese Patent Laid-Open No. 59-99336, the target value of the measurement output of each element in a standard sample is stored in a memory in advance, and the photomultiplier tube is sequentially read based on the data read from the memory by a program. The sensitivity is automatically adjusted, which has the advantage of reducing the work load on the operator, but it is necessary to set the target estimated value for each sample in advance and the actual content exceeds the estimated range. And there is a drawback that you can not analyze.

(Problems to be Solved by the Invention) The present invention provides a photometric device for emission spectroscopic analysis, which can always automatically adjust the photomultiplier tube to the optimum sensitivity without setting a target value in advance as described above. The purpose is to do.

(Means for Solving the Problems) In order to achieve the above object, the photometric device according to the present invention is
Means for comparing the detection output of the photomultiplier tube with a constant value or a value in a predetermined range, and feeding back the comparison output to the applied voltage of the photomultiplier tube to change the amplification factor of the photomultiplier tube; Is detected and converted into an amplification degree based on the correlation data of the applied voltage and the amplification degree which are stored in advance, and a photometric value is calculated as a ratio of the detection output and the amplification degree.

(Operation) According to the above configuration, the amplification factor of the photomultiplier tube is controlled steplessly, and the optimum sensitivity to the light input is always maintained. It is not necessary to switch the range, and the SN ratio is also improved.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which the output of the photomultiplier tube 1 is converted into a voltage signal by a parallel circuit of a resistor R and a capacitor C and then amplified by an amplifier 2, The obtained detection output Va is compared with the reference voltage Vb by the differential amplifier 3,
By inputting the output of the differential amplifier 3 to the negative high-voltage power supply circuit 4, the applied voltage Vd of the photomultiplier tube 1 is controlled to change the amplification factor f (V) of the photomultiplier tube 1. The applied voltage Vd to the photomultiplier tube 1 is converted into a digital value by the A / D converter 5 and read by the microprocessor 6,
This is the amplification factor f (V) using the correlation data between the applied voltage Vd and the amplification factor f (V) stored in the memory in advance.
And the detected output Va is divided by the amplification factor f (V) to calculate a photometric value. The photometric value thus obtained is output to the output device 7 such as a CRT or a pen recorder.

FIG. 2 shows the correlation characteristic between the applied voltage Vd and the amplification degree f (V), and this characteristic is stored in advance in the memory of the microprocessor 6 as a functional expression or a conversion table.

According to this structure, the sensitivity of the photomultiplier tube 1 is continuously controlled so that the detection output Va is always constant in accordance with the magnitude of the light input, so that the standard sample is used in advance as in the conventional case. The measurement range is set for each element,
Alternatively, there is no need to detect the scale-up of the detection output and switch the measurement range stepwise, and the S / N ratio is always kept at the highest level.

FIG. 3 shows another embodiment in which the output of the photomultiplier tube 1 is input to the microprocessor 6 via the A / D converter 8 to supply a voltage to the photomultiplier tube 1 at a negative high voltage. Power supply 4
Input data Do from the microprocessor 6 via the D / A converter 9 and store a correlation table between the output data Do and the amplification factor f (V) of the photomultiplier tube 1 in the microprocessor 6. Then, the output data Do is changed in the microprocessor 6 until the input data Di from the A / D converter 8 falls within a predetermined range, and the above-mentioned input data is obtained at the amplification degree f (V) of the photomultiplier tube 1 at this time. It is the one in which the photometric value is calculated by dividing Di.

With this configuration, the resolution of the number of bits obtained by adding the A / D converter 8 and the D / A converter 9 as the photometric value can be obtained, and the number of effective digits is always the same regardless of the size of the optical input. Has the advantage that it can measure a wide dynamic range.

As described above, according to the present invention, the sensitivity of the photomultiplier tube is controlled by feeding back the voltage applied to the photomultiplier tube so as to keep the detection output of the photomultiplier tube constant. With
This applied voltage is detected, converted into an amplification degree using the correlation data between the applied voltage and the amplification degree, and the photometric value is calculated from the detection output and the amplification degree. It is said that there is no need to estimate the amount of each element in the sample and set the sensitivity for each element in advance, the sensitivity adjustment can be completely automated, and a good SN ratio can be maintained in a wide dynamic range. There are advantages.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the operation of the same, and FIG. 3 is a block diagram showing another embodiment of the present invention. 1 ... Photomultiplier tube, 2 ... Amplifier, 3 ... Differential amplifier, 4 ... Negative high voltage power supply, 5 ... A / D converter, 6 ... Microprocessor, 7 ... Output device, 8 ... ... A / D converter, 9 ... D / A converter.

Claims (1)

[Claims] 1. A means for comparing the detection output of the photomultiplier with a reference value and feeding back the comparison output to the applied voltage of the photomultiplier to change the amplification factor of the photomultiplier, and the applied voltage. Is detected, and is converted into an amplification degree according to the correlation data between the applied voltage and the amplification degree stored in advance, and a photometric value is calculated as a ratio of the detection output and the amplification degree. A photometric device for emission spectral analysis.