JP2675954B2 - Calibration method for mass spectrometric gas leak detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calibrating a mass spectrometric gas leak detector for testing the airtightness of devices and equipment used in various industries.

[0002]

2. Description of the Related Art Communication cables are one of the fields in which airtightness is required. As for communication cables, important intercity cables and city cables with a large number of lines are large so that moisture and water do not enter the cable and cause line failure even if the cable is submerged in water. Dry gas (dry air or nitrogen gas) is filled at a pressure higher than atmospheric pressure and gas maintenance is performed. Conventionally, as a method of detecting gas leakage in a gas-maintained communication cable (hereinafter abbreviated as a gas cable) and its connecting portion, soapy water is used as a cable in a visually recognizable area within the reach of an operator. The ultrasonic wave generated when gas leaks from a pinhole is collected by a microphone, converted into an audible frequency and amplified, and detected by an earphone. Also, if the search for leaks is extensive,
When checking for leaks of cables drawn into underground pipelines, a method has been adopted in which the cable to be detected is filled with CFC gas and the presence or absence of gas leaks is checked using a CFC detector using the Rice effect. Was. The latter method is D
This method was developed as a gas inspection method and has a long track record. However, in recent years, destruction of the ozone layer by Freon gas has become a problem on a global scale, and the ban on the use of Freon gas is about to be implemented immediately.

There are two types of gas cables of this type: so-called elevated cables stretched between utility poles and underground cables laid underground. Of these, underground cables are usually buried between manholes. It is housed in a pipeline that has been opened. Due to the depth, space, size of entrances and exits, and ventilation, manholes can only carry the minimum necessary equipment into the manhole. Therefore, except for portable devices, precision instruments have to be installed outside the manhole. Until now, a precise mass spectrometric gas leak detection device has never been used in the field of communication equipment maintenance. When using the conventional mass spectrometric helium leak detector outdoors,
Due to the influence of dust and the like, there is a possibility that trouble such as device failure may occur.

The inventors of the present invention have filed a patent application for the purpose of downsizing, high accuracy, and improvement of operability in a field environment of a mass spectrometric gas leak detector which is theoretically the highest in detection sensitivity. Patent applications have been filed as Japanese Patent Application Laid-Open No. 4-192380 “Mass Spectrometric Gas Leak Detector” and Japanese Patent Application No. 4-2877861 “Mass Spectrometric Gas Leak Detector”. Said Japanese Patent Application No. 4-
No. 192380 discloses a technique for an internal calibration method for a detector using nitrogen in air as a reference gas.
This method is suitable for canceling the time drift characteristic of the electronic circuit performance that occurs when the detector is operated for a long time. Further, in the above-mentioned Japanese Patent Application No. 4-287861, in order to ensure high sensitivity, maintainability, and operability even in a bad measurement environment with a lot of dust and the like, a warning display regarding device maintenance such as filter clogging is displayed. The technology is disclosed about the function.

[0005]

DISCLOSURE OF THE INVENTION The present invention further improves the method disclosed in Japanese Patent Application No. 4-192380 based on experience in the field, improves measurement accuracy, and lowers the cost of the apparatus. An object of the present invention is to provide a calibration method for a mass spectrometric gas leak detector with improved operability. That is, the present invention provides a method for correcting the unavoidable time drift characteristic of an electronic circuit to optimize the applied voltage for detection gas detection when measurement accuracy is required. The applied voltage corresponds to, for example, the acceleration voltage of the detection gas ions when the mass analysis unit of the mass spectrometry gas leak detector is of the magnetic field deflection type, and the mass analysis unit of the mass spectrometry gas leak detector has four In the case of a quadrupole mass filter, it corresponds to a DC voltage or an AC voltage applied to the quadrupole rod.

[0006]

In order to solve the above problems, the present invention provides a mass spectrometric gas leak in which the mass spectrum scanning voltage is fixed to the mass number of the detection gas and the detection gas is continuously measured. A detector, and during the internal calibration of the detector,
Mass spectrum sweeping is performed to obtain the mass spectrum of one gas of the air component gas, and the fixed voltage of the detection gas at the time of measurement is determined with reference to the sweep voltage corresponding to the peak value of the mass spectrum of the component gas. It is characterized by automatic correction.

Further, when the air component gas is nitrogen and the nitrogen concentration obtained by mass spectrometry is used as a reference,
It is characterized in that the detected gas concentration is calibrated.

[0008]

According to the above-mentioned Japanese Patent Application No. 4-192380, in the case of precision measurement, since the mass spectrum was swept at a constant repetition period, it could not be measured in real time, but the method of the present invention was used. However, once the applied voltage is optimized by the above means, the time drift of the applied voltage can be eliminated, so that the detection gas can be continuously measured with high accuracy.

[0009]

FIG. 2 is a characteristic diagram for explaining the principle of a calibration method for a mass spectrometric gas leak detector according to the present invention, in the case where the detector operates normally, and FIG. 3 is a mass spectrometric type according to the present invention. It is a characteristic view explaining the principle of the calibration method of a gas leak detector, and is a case where an applied voltage causes a time drift.

That is, a mass spectrometric gas leak detector for continuously measuring the detection gas by fixing the mass spectrum sweep voltage to the mass number of the detection gas, which is a method for correcting the time drift of the detector. The principle will be described with reference to the drawings. 2 and 3
2 shows mass spectra of nitrogen and helium. FIG. 2 is an explanatory diagram when the detector is calibrated and is normal, and FIG. 3 is an explanatory diagram when the applied voltage changes due to time drift. In FIG. 2, the applied voltages of nitrogen (N; m (mass number) / e (charge number) = 7) and helium (He; m / e = 4) are V1 and V2, respectively, and the spectral intensity is
H1 and H2, respectively. The applied voltages of nitrogen and helium are ΔV1 and ΔV2, respectively, due to the time drift.
When it fluctuates, the spectral intensities are H1 'and H
2 '. During normal measurement, the helium concentration is fixed at V2, and since the applied voltage drifts by ΔV2 in order to obtain it from the helium ion current value at that time, even if the helium concentration is the same, the helium concentration changes from H2 to H.
It will be reduced to 2 '. In the conventional helium leak detector, so that the time drift of the applied voltage is small,
A method of obtaining a peak value of helium by using a highly stable electronic circuit or performing mass spectrum scanning for each measurement has been used. Japanese Patent Application No. 4-192 mentioned above
In the precision measurement mode of No. 380, the latter method was adopted. Mass spectrum scanning has a drawback that real-time measurement is impossible.

On the other hand, in the method of the present embodiment, the nitrogen spectrum is obtained by voltage sweeping in the range of m / e = 8 to 6 during internal calibration of the detector,
V2 is corrected by the voltage fluctuation value ΔV1 calculated from the peak value. Since m and e are close to each other for nitrogen and helium, ΔV1 and ΔV2 are almost equal. Especially,
In the case of the quadrupole mass filter, since the mass spectrum has a characteristic that it appears at equal intervals with respect to the applied voltage in principle, ΔV1 and ΔV2 can be regarded as equal.
Therefore, after the correction, the peak value of the helium spectrum can be measured by using V2 + ΔV1 instead of V2 as a new applied voltage. In the magnetic field deflection type, theoretically, the larger the mass spectrum, the smaller the spectrum interval with respect to the applied voltage. Therefore, when m / e of nitrogen and the detection gas are distant from each other, ΔV2 may be multiplied by a constant coefficient m and V2 + mΔV1 may be applied voltage. The value of m may be obtained experimentally in reality.

In addition, by actually obtaining the helium spectrum,
Of course, a method of directly obtaining ΔV2 is also possible, but in this case, it is necessary to use helium gas, so that it cannot always be carried out at any time and anywhere. When the method of the present invention is used, nitrogen in the air is used to correct the time drift of the applied voltage, so that the method can be performed anytime, anywhere. Further, since the spectrum sweep is only for one spectrum and the sweep width is narrow, there is an advantage that the time required for calibration is short. And since no special gas for calibration is used, calibration is performed at any time when the detector is raised or when high-precision measurement is required, and at the time of calibration, simply press the calibration button on the detector operation panel surface. Calibration is complete. As described above, the method of the present invention has an advantage of excellent operability.

As described above, the present embodiment provides a method of canceling the time drift ΔV2 of the applied voltage and automatically correcting it to the correct V2. Therefore, it is not necessary to use expensive electronic circuit parts and High-accuracy measurement is possible with this grade component, and it is effective in reducing the cost of the detector. Of course, the detection gas is not limited to the above-mentioned helium, but the method of this embodiment can be applied to any gas detection such as hydrogen. In addition to nitrogen, it is also possible to select oxygen as the air component gas. Also in the case of nitrogen, m / e = 7 is not limited to m / e = 7.

Various factors other than the above-mentioned time drift of the applied voltage can be cited as factors for varying the concentration of the detected gas. For example, filament performance, ion collector electrode performance deterioration, electronic circuit system gain reduction, and the like. These fluctuation factors (which will be referred to as device constants) affect both nitrogen and the sensing gas to the same extent. Therefore,
When obtaining the detection gas concentration, by normalizing with the concentration of nitrogen, that is, by dividing the detection gas ion current value by the nitrogen ion current value and multiplying by a constant coefficient value, the detection gas concentration can be obtained. It is possible to cancel the influence of the fluctuation of the device constant. Then, as the nitrogen ion current value, the value registered in the memory is used, and if the value is updated next to the calibration, it is not necessary to measure the nitrogen ion current value at each measurement, so real-time measurement becomes possible. .

By implementing the method of the above-mentioned embodiment, a highly stable mass spectrometric gas leak detector that compensates for the time drift of the applied voltage and the fluctuation factor of the device constant can be economically provided.

The present invention will be described in more detail below.
The following are merely examples of the present invention and do not limit the technical scope of the present invention.

FIG. 1 is an example of a flowchart showing a calibration method for a mass spectrometric gas leak detector according to the present invention. The detector is equipped with a microcomputer, ROM and RAM, and the program and default data are written in the ROM. When the detector is activated, first, the applied voltage V1 for nitrogen detection is applied from the ROM to the RAM.
And the applied voltage V2 for detection gas detection are read (default value). Next, it is determined whether or not the device has just started up, and if it has just started up, the process branches to the flowchart on the right side. Also, the presence or absence of internal calibration is determined, and in the case of internal calibration, the process similarly branches to the flowchart on the right side.

Next, the case of internal calibration will be described. First,
The mass spectrum sweep start voltage Vs and the mass spectrum sweep end voltage Ve are read from the ROM into the RAM, and the applied voltage sweeps between Vs and Ve. Vs and Ve are set so as to cover nitrogen (m / e = 7). 2
The peak position of the nitrogen spectrum detected by the secondary ion detector is detected by the peak hold circuit, and the peak position voltage V1 'is measured. The nitrogen detection voltages V1 and V1 ′ read in advance in the RAM are compared to calculate a voltage drift amount ΔV2 (ΔV2 = V1−V1 ′), which is stored in the memory. Further, the nitrogen concentration b at the peak position is measured and stored in the memory. The subsequent process is the same as a normal measurement routine without internal calibration.

Next, a normal measurement routine will be described. First, the nitrogen concentration b is read from the memory. Then, the detection gas detection applied voltage correction (V2 ← V2 + ΔV2) is performed, the detection gas concentration a is measured, and the detection gas concentration correction (a ← k · a / b) is performed. The principle of applied voltage correction is as described above. The detection gas concentration is corrected by normalizing the gas specific to the present embodiment with the nitrogen gas concentration in order to compensate the electronic circuit characteristics, the time drift, and the characteristic variation of the mass spectrometric section. In other words, the aim is to cancel various characteristic fluctuations that can be regarded as device constants such as electronic circuit characteristics and mass spectrometric characteristics on both the detection gas and nitrogen gas at the same rate, so cancel by a / b division processing. It is in.

The detected gas concentration is obtained by multiplying a / b by a constant k. This constant can be set experimentally by measuring a detection gas of known concentration.

[0021]

As described above, the method of the present invention is a method suitable for digital processing and is unavoidable in an electronic circuit.
The time drift of applied voltage and gain is compensated. Therefore, it is not necessary to use expensive electronic circuit parts, high-accuracy and highly stable measurement can be performed with normal grade parts, and the effect of reducing the cost of the mass spectrometric gas leak detector is demonstrated.

Further, when the method of the present invention is used, the time drift of the applied voltage or the gain is corrected by using nitrogen or oxygen in the air, so that the method can be carried out anytime, anywhere. Further, the spectrum sweep is effective for one spectrum, and the sweep width is narrow, so that the time required for calibration is short. And since no special gas for calibration is used, calibration is performed at any time when the detector is raised or when high-precision measurement is required, and at the time of calibration, simply press the calibration button on the detector operation panel surface. Calibration is complete. Thus, the method of the present invention has excellent operability.

It should be noted that the detector according to the present invention is not limited to the leak detection of the gas cable, and is carried out in various fields such as the automobile industry, the air conditioner / refrigerator industry, the electronic component industry, and the nuclear industry. It can be applied to leak tests.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a calibration method for a mass spectrometric gas leak detector according to the present invention.

FIG. 2 is a characteristic diagram illustrating an example of the principle of the calibration method for a mass spectrometric gas leak detector according to the present invention, in the case where the detector operates normally.

FIG. 3 is a characteristic diagram for explaining an example of the principle of the calibration method for the mass spectrometric gas leak detector according to the present invention, in the case where the applied voltage causes a time drift.

[Explanation of symbols]

V1, V2, V1 ', V2' ... Applied voltage, H1, H2
H1 ', H2' ... Spectral intensity.

Claims (2)

(57) [Claims] 1. A mass spectrometric gas leakage detector for continuously measuring the detection gas by fixing the mass spectrum sweep voltage to the mass number of the detection gas, wherein the mass is measured when the detector is internally calibrated. by performing spectral swept, nitrogen of the air component gas
Obtains a mass spectrum of iodine or oxygen, the nitrogen also lay
Is the voltage fluctuation corresponding to the peak value of the oxygen mass spectrum
A method for calibrating a mass spectrometric gas leak detector, wherein the fixed voltage of the detection gas at the time of measurement is automatically corrected using the value . 2. The mass spectrometer according to claim 1, wherein one of the air component gases is nitrogen, and the detected gas concentration is calibrated with reference to the nitrogen concentration obtained by mass spectrum scanning. Method for calibrating gas leak detectors.