JPH0234430B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain detector for a secondary electron multiplier used, for example, in a mass spectrometer, an ion microanalyzer, or the like.

Conventionally, the only way to determine the gain of a secondary electron multiplier was to perform actual measurements at the beginning of use and find out the approximate gain obtained experimentally, and a decrease in gain was observed under actual usage conditions. At the time (which inevitably happens), it was not possible to know exactly how much the decline had changed or not.

For this reason, for example, in a mass spectrometer, when controlling the gain of the secondary electron multiplier tube according to the intensity of the chromatogram peak to improve the substantial dynamic range of ion detection, it is necessary to It has been difficult to realize this goal because accurate values cannot be ascertained.

An object of the present invention is to provide a secondary electron multiplier tube gain detector that can improve the substantial dynamic range of ion detection.

In order to achieve such an objective, the present invention
The relationship between the gain of the secondary electron multiplier tube and the digital reference signal of the high applied voltage is determined in advance and is stored in the memory as a table value.

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 1 is a block diagram showing an embodiment of a gain detector for a secondary electron multiplier according to the present invention. In the figure, there is a secondary electron multiplier tube 1, to which a high voltage of usually 0 to -3 kV is applied from a high voltage power source 2, and the gain is determined by the voltage. It's becoming like that. The output of the high voltage power supply 2 is determined by the output signal of the reference signal generating D/A converter 3, and the input digital signal of this D/A converter 3 is sent from the computer control section 6. It's becoming like that. On the other hand, the output current of the secondary electron multiplier 1 is detected by the current detector 4.
After being converted into voltage by the A/D converter 5 and digitized by the A/D converter 5, the signal is sent to the computer control section 6. Here, the current detector 4 has a configuration as shown in FIG.
For example, when the detection current exceeds 10 ^-6 A, the amplifier output is saturated and detection is no longer possible.
Therefore, the dynamic range can be expanded by reducing the digital input value of the D/A converter 3 and lowering the gain of the secondary electron multiplier 1 at this time.
However, in this case, it is required that the relationship between the digital input value and the gain of the secondary electron multiplier be clear. This is because if this relationship is not clear, even if you try to lower the gain to a certain value, you will not know the digital input value of the D/A converter 3 that corresponds to that value. This is because settings cannot be made by Therefore, means 8 for capturing a specific mass number
(Specifically, a means for setting a magnetic field or an accelerating voltage, etc.) is provided, and the intensity of the specific mass number peak, that is, the output of the A/D converter 5, is
Each time the input digital value of the D/A converter 3 changes, the computer control unit 6 reads the output of the A/D converter to see how it changes depending on the input digital value of the A converter 3. ,
The resulting correlations as shown in FIG. 3 are stored in the memory 7 as a table. In this case, it becomes possible to accurately reduce the gain to a certain value, and therefore it becomes possible to accurately increase the dynamic range. Furthermore, the gain of the secondary electron multiplier is
Since it changes over time, it is best to create the above table before measuring the sample.

As is clear from the above description, the gain device for the secondary electron multiplier according to the present invention can accurately control the dynamic range of the ion detector regardless of the change in diameter of the secondary electron multiplier. You will be able to give.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a gain detector of a secondary electron multiplier according to the present invention, FIG. 2 is a block diagram showing an embodiment of a current detector of the gain detector, and FIG. shows an explanatory diagram of data stored in memory. 1...Secondary electron multiplier tube, 2...High voltage power supply, 3...
D/A converter, 4...Current detector, 5...A/D
Converter, 6...computer control unit, 7...memory.

Claims (1)

[Claims] 1 A secondary electron multiplier tube, a high voltage power source for applying high voltage to the secondary electron multiplier tube, and a reference signal generator for controlling the high voltage power source, the reference signal generator including a D/A converter. , a secondary electron multiplier tube gain detection characterized in that a table representing the correlation between the input digital value of the D/A converter and the gain of the secondary electron multiplier tube is stored in advance in a memory. vessel.