JPH0359546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in magnetic field generators for mass spectrometers.

(Prior art) A mass spectrometer uses a mass spectrometer to accelerate ions (charged atoms or molecules) at a constant speed and pass them through a magnetic field. This is a device that measures the mass number of atoms or molecules by utilizing the property that their orbits are bent. Currently, it is combined with a gas chromatograph and used for measuring organic compounds such as pollution.

By the way, in this type of mass spectrometer, it is known that the detected mass number is proportional to the square of the magnetic field strength. Therefore, if the variable range (dynamic range) of the set magnetic field strength can be widened,
Accordingly, a wide range of mass numbers can be detected. Conversely, if the variable range of the set magnetic field strength is narrow, only mass numbers within a narrow range can be detected. The magnetic field of a mass spectrometer is usually generated by an electromagnet composed of a yoke provided with an air gap (hereinafter simply referred to as the gap) and a coil wound around the yoke. Specifically, current is passed through a coil wound around the yoke, and the resulting magnetic field generated in the gap is used as a magnetic field.

In order to be able to detect mass numbers in a wide range with such an electromagnet, it is necessary to configure the electromagnet so that the current flowing through the coil or the number of turns of the coil can be varied depending on the measurement range. On the other hand, depending on the application, the range of detected mass numbers may be narrow, but a high magnetic field sweep speed may be required. In such cases, it is necessary to design with the primary goal of improving the sweep speed of the magnetic field, so a split coil is installed to reduce the number of coil turns.
The number of turns of the coil is changed depending on the application.

FIG. 2 is a diagram showing a conventional embodiment of this type. In the figure, reference numeral 1 indicates a yoke having a gap g in a part thereof, and reference numerals 2 and 2' indicate magnetic field generating coils wound around the yoke 1. A tap is pulled out from part of the coils 2 and 2', and a selector switch is activated.
The number of coil turns can be switched in two stages by SW ₁ and SW ₂ . That is, the changeover switch
SW ₁ and SW ₂ are switched in conjunction with the a-contact or b-contact side, so that two stages of the number of coil turns can be obtained. When the changeover switches SW ₁ and SW ₂ are on the a-contact side, the number of turns decreases, and when they are on the b-contact side, the number of turns increases.

3 is a Hall element that detects the strength of the magnetic field in the gap g; 4 is a current control circuit that determines the value of the current flowing through the Hall element 3; 5 is a Hall voltage amplification circuit that amplifies the output voltage of the Hall element 3; 6; is a differential amplifier which receives the output of the Hall voltage amplification circuit 5 at one input and receives a reference voltage (magnetic field strength control reference voltage) Es corresponding to the magnetic field strength reference value at the other input. As the current control circuit 4, for example, a constant current circuit is used. The output of the Hall voltage amplification circuit 5 is
The signal is extracted externally as a magnetic field strength signal and displayed on, for example, a monitor meter. 7 is a differential amplifier 6
The buffer transistor E 1 driven by E ₁ is a power source that supplies current to the coils 2 and 2'.
The above-mentioned coils 2 and 2' serve as collector loads for the transistor 7, and the transistor 7 receives the drive signal from the differential amplifier 6 as a base and outputs the coils 2, 2'.
2'.

(Problems to be Solved by the Invention) The device configured in this manner constitutes a negative feedback circuit, and the magnetic field strength control reference voltage Es and the magnetic field strength signal detected by the Hall element 3 become equal. The magnetic field in the gap g is controlled as follows. In this device, the magnetic field strength control reference voltage
The gain of each component (for example, differential amplifier 6) is adjusted so that the maximum value _of Es (maximum control value of magnetic field strength) is equal to the maximum magnetic field strength signal when it is on the _b contact side of the changeover switches SW 1 and SW 2. It is becoming more and more determined.

Next, in this state, changeover switches SW ₁ and SW ₂ are set to a.
When operated on the contact side (when operated in a narrow mass number range), the magnitude of the magnetic field strength control reference voltage Es is a lower voltage value than when the changeover switches SW ₁ and SW ₂ are on the b contact side. is sufficient. or,
In this case, the magnetic field strength signal obtained from the Hall element 3 also naturally takes a low voltage value because the number of turns is reduced. For example, a wide mass number range (10000 as an example)
Magnetic field strength control reference voltage in case of configuration that detects
If the value of Es is 10V, the magnetic field strength control reference voltage when detecting a narrow mass number range (1000 as an example)
The Es and magnetic field strength signals are approximately 3V. Therefore, if the configuration for detecting a wide mass number range is used to detect a narrow mass number range, only 1/3 of the control circuit's dynamic range will be used, and the remaining 2/3 will be used to detect a narrow mass number range. range is unused,
It will be wasted. The control circuit is best in terms of accuracy and noise when used near the full scale of the dynamic range. Therefore, when used within the dynamic range of 1/3, the control accuracy becomes three times worse and the noise characteristics also become worse.
Further, the use of the magnetic field strength control reference voltage is also wasteful.

The present invention has been made in view of these points, and its purpose is to provide dynamic range detection in both a wide mass number range and a narrow mass number range without making any particular changes to the configuration of the control circuit. The object of the present invention is to realize a magnetic field generator for a mass spectrometer that can operate a control circuit near the full scale of the mass spectrometer.

(Means for Solving the Problems) The present invention, which solves the above problems, includes a coil winding number switching means for switching the number of turns of the coil wound around the yoke, and a means for detecting the magnitude of the magnetic field generated in the air gap of the yoke. a Hall element, a coil driving means for driving the coil according to the output of the Hall element, and a Hall current switching means for switching a current value flowing through the Hall element, and a switching operation of the coil turns switching means. The present invention is characterized in that the switching operation of the Hall current switching means is performed in conjunction with the switching operation of the Hall current switching means.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Components that are the same as those in FIG. 2 are designated with the same numbers. In the figure, 4' is a changeover switch SW ₁ ,
In conjunction with SW ₂ , change the value of the current flowing through Hall element 3.
Changeover switch for switching between two types: I ₁ and I ₂
This is a current control circuit equipped with SW ₃ . When the coil turns selection switches SW ₁ and SW ₂ are switched to the a contact side, SW ₃ is also switched to the a contact side, and the changeover switch is switched to the a contact side.
When SW ₁ and SW ₂ switch to the b-contact side, SW ₃ is also synchronously switched to the b-contact side.
When the changeover switch SW ₃ is on the a contact side, the current control circuit 4' outputs the current _I1 , and when the changeover switch _SW3 is on the b contact side, the current control circuit 4' outputs the current _I2. (I ₂ > I ₁ ) is output. The operation of the device configured as described above will be explained as follows.

The Hall element 3 utilizes the so-called Hall effect, and generates a DC voltage according to the magnetic field strength (magnetic flux density) B.
It outputs _VH . In order to operate this Hall element 3 normally, it is necessary to flow a current I perpendicular to the direction of the magnetic field. At this time, the output V _H of the Hall element 3 is calculated by the following formula, where the flowing current I and the self-flux density B are is given by

V _H =K×I×B The current I shown in the above equation is given from the current control circuit 4'.

FIG. 3 is a diagram showing the Hall voltage output characteristics of the Hall element 3. The vertical axis shows the Hall voltage V _H and the horizontal axis shows the magnetic field strength (magnetic flux density) B. In the figure, f ₁ is the characteristic when the output current is I ₁ when the changeover switches SW ₁ to _{SW 3} are set to the B contact side, and f ₂ is the characteristic of the changeover switch.
The characteristics when the output current is _I2 are shown when _SW1 to _SW3 are set to the a contact side. Characteristic curve f ₁ ,
Let the corresponding magnetic flux densities when f ₂ reach the maximum magnetic field strength signal line L be B ₁ and B ₂ , respectively. From the figure, if we change the value of the current flowing through the Hall element 3, even if the magnetic field strength becomes small, the output _VH of the Hall element 3 will have the same full-scale amplitude voltage value as in the case of wide mass number range detection. I know what I can get.

Therefore _, when detecting a wide mass number range by setting _{the changeover switches SW 1 and} SW ₂ to the b contact side, the current control circuit ₄ ' can know the detection range. Once the detection range is confirmed,
The current control circuit 4' outputs a corresponding current I ₁ to flow through the Hall element 3. On the other hand, the changeover switch SW ₁ ,
When SW ₂ switches to the a contact side, the changeover switch SW ₃
is also switched to the a-contact side in conjunction, and notifies the current control circuit 4' that the measurement range has been switched to the narrow mass number range detection range. Upon receiving this signal, the current control circuit 4' switches the output current from the current I ₁ to a larger value I ₂ and causes it to flow through the Hall element 3.

According to the present invention, by switching the current flowing through the Hall element 3 in synchronization with the switching of the coils 2 and 2', the output of the Hall element 3 is achieved regardless of the magnitude of the magnetic field strength in the gap g. can always be brought close to full scale (for example, 10V). Therefore, since the differential amplifier 6 can also be operated near the maximum dynamic range, control accuracy is improved regardless of the measurement range. Therefore, the generated magnetic field strength is also accurate and stable. Furthermore, since the device is operated near full scale, noise characteristics are also improved.

In the above description, the case of two-step switching of the measurement range has been described, but the present invention is not limited to this, and can be similarly applied to a case where an arbitrary number of measurement ranges are provided.
That is, the configuration is such that the number of types of current equal to the number of switching stages of the coil wound around the yoke 1 can flow through the Hall element 3, and in conjunction with the switching of the coil, the current control circuit 4' flows through the Hall element 3. 3 by changing the value of the current I. In addition, in the above explanation, the current control circuit 4' is a changeover switch that operates in conjunction with the changeover switches SW ₁ and SW ₂ .
Although we have explained the case of checking the range switching using the contacts of SW ₃ , it is not necessarily necessary to use the changeover switch SW ₃ .
Any means may be used as long as it operates in conjunction with SW ₁ and SW ₂ . Although the present invention has remarkable effects when used in mass spectrometers,
It goes without saying that it can also be used as a magnetic field generator for all purposes.

(Effects of the Invention) As explained in detail above, according to the present invention,
By changing the value of the current flowing through the Hall element in conjunction with switching the number of turns of the coil, control around full scale is always possible. Therefore, according to the present invention, a stable and highly accurate magnetic field can be generated in any mass detection range.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows an example of a conventional device, and FIG. 3 is a diagram showing the output characteristics of a Hall element. 1... Yoke, 2, 2'... Coil, 3... Hall element, 4, 4'... Current control circuit, 5... Hall voltage amplification circuit, 6... Differential amplifier, 7... Transistor, E ₁ ... Power supply, Es... Magnetic field strength control reference voltage, SW ₁ to _{SW 3} ... Changeover switch.

Claims (1)

[Claims] 1. A coil winding number switching means for switching the number of turns of the coil wound around the yoke, a Hall element that detects the magnitude of the magnetic field generated during the air gap of the yoke,
It consists of a coil driving means for driving the coil according to the output of the Hall element, and a Hall current switching means for switching the current value flowing through the Hall element. 1. A magnetic field generator for a mass spectrometer, characterized in that the device is configured to perform a switching operation of a current switching means.