JPH0358142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a quadrupole mass spectrometer.

(Prior art and problems) A quadrupole mass spectrometer is divided into an ion meter, a quadrupole electrode, and a detection section. The opposing rod electrodes are connected to each other, and a DC voltage (U) of ±(U+Vcosωt) superimposed with a high frequency voltage (Vcosωt) having a frequency of several megahertz is applied to each of them. The resolution of this type of mass spectrometer is greatly influenced by the stability of the U/V ratio. In order to keep this ratio constant, a common method is to detect the high frequency voltage to generate positive and negative DC voltages, and to superimpose this on the high frequency voltage. A crystal resonator is often used as an oscillation element to obtain a highly stable high-frequency voltage, but
Because the high-frequency voltage is a high voltage of several hundred volts or more, vacuum tubes are still often used, and the high-frequency transformer used in the output circuit uses air-core solenoids to improve temperature stability. High frequency output circuits require a considerable amount of space. In addition, some small quadrupole mass spectrometers are made smaller by using pot-core high-frequency transformers, but pot-core coils have poor stability due to temperature, so special circuits such as temperature compensation circuits are required. It's coming.

Further, on the secondary output side of the high frequency transformer, there are two coils wound evenly and tightly, and each coil is connected to the cylindrical rod electrode of the quadrupole via a high frequency cable and a vacuum terminal. At this time, the resonant frequency of the resonant circuit created by all the capacitances between the four electrodes and the ground, the high frequency cable, etc., and the inductance created by this one coil is the high frequency supplied from the primary side. must match the frequency of However, this high-frequency cable itself has a line-to-line capacity of about 100 picofarad per meter.
I can't make the cable too long. That is, in the case of a long cable, the loss due to the capacitance of the cable is large, so that high frequency power cannot be sufficiently transmitted to the quadrupole section.

That is, there exists a relationship of =1/2π√LC (here, π is pi) between the resonant frequency of the circuit, the inductance L of the coil, and the electric capacitance C, so that L and C are inversely proportional. Therefore, increasing the length of the cable and increasing C means that L must be decreased, but in order to obtain a high voltage, it is advantageous for L to be as large as possible. In other words, the recent trend is to use semiconductors for amplification elements, but the higher the frequency of semiconductors, the more difficult it is to increase the withstand voltage, so the voltage supplied to the primary side of the high-frequency coil ends up being about 100V or less. However, with long cables, in order to reduce L on the secondary side, the number of turns on the secondary side cannot be extremely large compared to the number of turns on the primary coil, making it difficult to boost the voltage using this high-frequency transformer, and the circuit design must also be sophisticated. In addition to requiring technology, high-resolution, high-mass spectrometers had to rely on high-voltage vacuum tube systems, making it difficult to convert them into semiconductors.

To deal with this problem, in commercially available quadrupole mass spectrometers, the high frequency cable is 1 meter or more, often 10 cm, and the RF devices such as the high frequency transformer, high frequency amplifier, high frequency oscillator, etc. are bundled together. Place it in the case and use this
The control body that drives the RF device is this RF
It is connected to the device using a separate cable, making it a two-stage system. For this reason, the RF equipment section becomes considerably large, and
It had to be installed in a halfway place, which greatly restricted its use. In addition, since the RF section is only a short distance from the quadrupole section, when the quadrupole section is used under severe conditions,
The problems were also big. That is, when heating the quadrupole section, a large cooling device is required to cool the RF device. Furthermore, when used in a chemical factory or the like where corrosive gases are floating, the RF section must be sealed, but it is difficult to dissipate the heat generated by the RF section, which tends to cause problems. Furthermore, when used in places with strong radiation such as accelerator equipment or nuclear fusion reactors, it is necessary to protect the RF part by surrounding it with lead, etc. However, in this case, as the RF part is large, it is not possible to completely shield it. Currently, it cannot be used in such environments because it is difficult, heavy, and has problems with heat dissipation.

(Objects and means of the present invention) The present invention was devised in view of the current situation, and its purpose is to provide a high-frequency output transformer section that supplies high-frequency power to quadrupole electrodes, By arranging the high-frequency amplification element section separately via a high-frequency transmission cable, the portion close to the quadrupole electrode section can consist of only a high-frequency transformer, or a high-frequency transformer and several diodes.
Alternatively, by using only vacuum tubes, resistors, and capacitors, it can be made smaller and lighter, making radiation shielding, chemical shielding, etc. easier and more reliable, eliminating heat emission from the high frequency circuit itself, and eliminating heat emission from the quadrupole electrode. This is an attempt to solve the conventional problems all at once by separating the amplifying element, which has large instability due to temperature rise even if there is heat conduction.

In addition, this method eliminates the need for a high-frequency transmission cable after the high-frequency transformer outputs, so the capacitance C including the quadrupole electrode can be minimized, so the inductance L of the high-frequency output transformer can be maximized, and the high-frequency power It is very easy to increase the voltage. In other words, in the past, a high frequency cable was used between the quadrupole electrode part and the high frequency transformer, so it was not possible to make a long cable, whereas in the present invention, the high frequency cable is connected to the high frequency transformer,
This problem was solved by placing it between the high frequency amplification elements. Therefore, the high-frequency voltage applied to the primary input side of the high-frequency transformer can be lowered, and the commercially available 75
This is an innovative product that can be used with low characteristic impedance cables ranging from Ω to 50 Ω, allowing high-frequency cables to be extended to approximately 50 meters without any problems.

(Example) Hereinafter, the present invention will be described with reference to an example that can be illustrated.

FIG. 1 is a block diagram of an RF circuit for explaining the present invention. 1 is an RF oscillator stabilized by a crystal resonator with a frequency of 3.5MHz.

This output is amplified by a preamplifier, and then sent to a high frequency power amplifier 2, where it is amplified and becomes an output. Reference numeral 3 denotes a transmission line transformer for matching with the high frequency transmission cable 4 having a characteristic impedance of 75Ω, and is not necessary if the output impedance of the high frequency power amplifier 2 is close to the impedance of the transmission cable 4.

Furthermore, since the purpose of the transmission line transformer 3 is to achieve impedance matching, the high frequency transmission cable 4 is effective even when the primary input impedance of the tank circuit 5, that is, the high frequency transformer is far from the characteristic impedance of the transmission cable 4. and the tank circuit 5. 4 is a coaxial type high frequency transmission cable, and the characteristic impedance is 75Ω as an example, but it may be 50Ω or other value. 6 is a quadrupole analysis section, 7 is a feedback output cable, and 8 is an offset input circuit.

By the way, the tank circuit 5 is constructed as shown in FIG. That is, the tank circuit 5 is an embodiment in which a trochoidal core 9 is used as a high frequency transformer to achieve miniaturization. In the embodiment shown in the figure, the output of the transmission cable 4 is directly input to the primary coil of three turns of silver diefron wire with a wire diameter of 0.8 mm.
Reference numerals 11 and 11' denote high-frequency, high-voltage output secondary windings, which are wound in opposite directions to invert the phases. The number of turns of 11 and 11' is 15, which is 5 times the number of primary turns of 3, so the resulting high-frequency secondary output is 5 times that of the primary input, and is 100Vpp.
A secondary output of 500Vpp can be obtained from the primary input.

The secondary winding 12 is for feedback output, and is converted into a DC signal by a feedback rectifier circuit 14 and fed back to the oscillation circuit 1 to stabilize the circuit. 2
The secondary winding 13 is for creating a DC component to be superimposed on the high frequency, and after being rectified by a diode bridge 15a provided in the DC component generation circuit 15, the output obtained through the smoothing circuit 15b is output to the secondary winding 11. ,1
It is added to the output of 1'. Further, an offset voltage is applied from the outside through the offset input circuit 8, and the DC component is eliminated to be used for total pressure measurement. Reference numeral 16 denotes an insulating wall (DC cutting capacitor) that isolates the vacuum from the atmosphere, and high-frequency power is supplied to the quadrupole rod electrode 17 through a conductor wire that is tight in the vacuum.

What is noteworthy about this example using a trochoidal coil is that since the coil is a trochoidal type, the number of turns of the coil is small, and the inductance can be determined accurately, so the variation when commercialized is minimized. This is something that can be done. In addition, since the DC component is taken from the secondary winding side, the ratio of the DC component to the AC component is always constant, resulting in very good stability.Furthermore, since the feedback output is obtained from the secondary winding, accurate mass determination is possible. It becomes possible. In other words, since it is stabilized by the voltage from the secondary output side, even if there is a slight deviation in the input impedance of the primary coil, the output impedance of the secondary high-frequency circuit, the frequency, etc., there is no mass in determining the mass, and the temperature stability is very good.

In particular, in the embodiment shown in Fig. 2, the relative magnetic permeability of the trochoidal core is selected to be small, so that the Curie temperature can also be reduced.
The temperature is over 400℃, so magnetic saturation due to primary side current is unlikely to occur, so there is no risk of the circuit running out of control. Furthermore, since the trochoidal coil is used for miniaturization, the tank circuit 5 shown in Figure 2 is housed in a metal case with a diameter of about 3 cm and a length of about 6 cm, making it possible to reduce the size to the same size as a cable connector. ing. In contrast, the size of the general (conventional) RF section currently in use with equivalent performance is 0.5 in volume.
-Many of the 2nd place and large 10th place items can not only be made smaller to about 1/10 to 1/200 of the conventional size, but can also be wrapped entirely in a lead plate to protect it from radiation. , a quadrupole mass spectrometer equipped with a high-frequency power transmission system that is extremely stable and easy to operate, with no heat build-up even when it is sealed from chemicals, and no heat is generated from the tank circuit. It provides:

(Effects) As described above, the present invention provides a high-frequency output circuit for high-frequency power applied to the quadrupole electrodes of a quadrupole mass spectrometer, in which a high-frequency amplification element section and a high-frequency output transformer section are connected via a high-frequency transmission cable. Because it is separated and arranged, it can be
In addition to being lightweight, shielding such as radiation shielding and chemical shielding can be done easily and reliably, eliminating heat emission from the high frequency circuit itself, and allowing heat conduction from the quadrupole electrode. However, it is possible to separate the amplification element, which has large instability due to temperature rise, and it is easy to use as it reduces installation space and environmental constraints, and it also requires particularly advanced technology in circuit design. Even in the case of a high-mass spectrometer with high resolution, it is possible to easily convert it into a semiconductor. In addition, in the present invention, a high frequency transmission cable is not required after the high frequency transformer is output, and the capacitance including the quadrupole electrode can be minimized, so the inductance of the high frequency output transformer can be maximized, and thus the inductance of the high frequency output transformer can be maximized. High-voltage high-frequency power can be easily achieved, and furthermore, the high-frequency voltage applied to the primary input side of the high-frequency transformer can be lowered by intervening the high-frequency transmission cable.
Since a low characteristic impedance cable of approximately 75Ω to 50Ω can be used, the high frequency transmission cable can be extended to approximately 50 meters without any problems, and in addition, a quadrupole mass spectrometer is obtained that is extremely stable and has excellent operability. This is an epoch-making invention that has many useful new effects, such as the ability to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is also an electrical circuit diagram. In the figure, 1 is a high-frequency oscillator, 2 is a high-frequency power amplifier, 3 is a transmission line transformer, 4 is a high-frequency transmission cable, 5 is a tank circuit, 6 is a quadrupole analysis section, and 9 is a trochoidal core.

Claims (1)

[Scope of Claims] 1. In a high-frequency output circuit for high-frequency power applied to the quadrupole electrodes of a quadrupole mass spectrometer, a high-frequency amplification element section and a high-frequency output transformer section are arranged separately via a high-frequency transmission cable. A quadrupole mass spectrometer featuring: 2. The quadrupole mass spectrometer according to claim 1, characterized in that a transmission line transformer is used in combination with the high frequency transmission cable. 3. The quadrupole mass spectrometer according to claim 1, characterized in that a toroidal core is used in the high frequency output transformer arranged via a high frequency transmission cable. 4. A quadrupole mass spectrometer according to claim 1, characterized in that the primary input side impedance of a high-frequency output transformer arranged via a high-frequency transmission cable is matched to the characteristic impedance of the high-frequency transmission cable. . 5. Claim 1, characterized in that a secondary output for obtaining a DC component to be superimposed on the high frequency output is provided on the secondary output side of the high frequency output transformer arranged via the high frequency transmission cable. Quadrupole mass spectrometer. 6. Claim No. 6, characterized in that a secondary output for obtaining a feedback signal necessary for stabilizing the output is provided on the secondary output side of a high-frequency output transformer arranged via a high-frequency transmission cable. The quadrupole mass spectrometer according to item 1.