JPH11182960A - Cryogenic refrigerating machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high performance cryogenic refrigerating machine in which noise generation is suppressed by interposing a noise filter between a power supply and a valve motor. SOLUTION: An inverter 17 is disposed in the compressor unit 15 of a refrigerating machine 10 and a frequency converted voltage is supplied from the inverter 17 through a noise filter 18 to a valve motor in the refrigerating machine 10 for cooling a magnet 7 in a shield 13. Consequently, a high frequency noise superposed on the voltage from the inverter 1-7 can be removed through the filter 18. According to the arrangement, rotational frequency of the valve motor in the refrigerating machine 10 can be controlled continuously with a low noise frequency converted voltage and the refrigerating capacity of the refrigerating machine 10 can be controlled continuously with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a cryogenic refrigeration system used for a superconducting magnet cooling system or the like.

[0002]

2. Description of the Related Art A superconducting magnet used in an MRI (Magnetic Resonance Imaging Diagnostic Apparatus) or the like must be cooled to an extremely low temperature of 10 K or less in order to maintain a superconducting state. By the way, in recent years, refrigerating machines have made remarkable progress, and the refrigerating capacity can be precisely and precisely controlled. In particular, in an expansion refrigerator such as a two-stage Gifford McMahon refrigerator, the expansion chamber provided at the tip of the second cylinder is divided into a high-pressure chamber to which high-pressure gas is supplied from the compressor and a low-pressure gas returned to the compressor. The refrigerating capacity can be steplessly controlled by controlling the switching cycle of a cylinder valve that is connected to and connected to the low-pressure chamber to which is supplied.

The switching cycle of the cylinder valve is controlled by supplying modulated electric power to a valve driving motor to control a rotation frequency. Specifically, an AC motor is used as the valve drive motor, and the frequency of the supply voltage is controlled by an inverter. Alternatively, a stepping motor is used as the valve drive motor, and the switching frequency of the stepping motor on / off is controlled by a pulse frequency generator.

[0004]

In the above-mentioned MRI, electric noise is very disliked for measuring a magnetic field change of a patient, and a room where the MRI is installed is shielded.
Various noises are prevented from entering the MRI.

[0005] However, in such an environment, the conventional superconducting magnet cooling apparatus attempts to steplessly control the refrigerating capacity of an expansion refrigerator that cools the superconducting magnet using an inverter or a pulse motor. Then, the following problem occurs. That is, since the inverter or the pulse frequency generator itself is a source of high-frequency noise, the inverter or the pulse frequency generator is installed in a compressor unit installed in a machine room provided outside the seal. Even if stored, high-frequency noise will enter the shield via electrical wiring from the inverter or the pulse frequency generator to the refrigerator.

It is an object of the present invention to provide a high-performance cryogenic refrigeration system with reduced noise.

[0007]

In order to achieve the above object, an invention according to claim 1 is an electrode having a refrigerator having a valve for switching and connecting a refrigerant gas expansion chamber between a high pressure side and a low pressure side of a compressor. The low-temperature refrigeration apparatus includes a valve motor that drives the valve, a power source that supplies modulated power to the valve motor, and a noise filter that is interposed between the power source and the valve motor. And

According to the above configuration, the high frequency noise generated from the power source that supplies the modulated power to the valve motor of the refrigerator is prevented from being cut by the noise filter and entering the refrigerator.

According to a second aspect of the present invention, there is provided a cryogenic refrigeration system in which a refrigerant gas expansion chamber is switched between a high pressure side and a low pressure side of a compressor by a valve. It is characterized by including a power source for supplying modulated power to the valve motor, a simple noise filter and an insulating transformer interposed between the power source and the valve motor.

According to the above configuration, high frequency noise generated by the power source that supplies the modulated power to the valve motor of the refrigerator is cut by the simple noise filter. Further, noise that is not cut by the simple filter, such as sudden noise, is prevented from being cut by the insulating transformer and entering the refrigerator. Further, transmission noise returning from the refrigerator through the ground is also cut.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a configuration diagram of a superconducting magnet cooling device using the cryogenic refrigeration device of the first embodiment. This superconducting magnet cooling device is a cooling device of a refrigerant system, in which a superconducting magnet is immersed in a refrigerant such as liquid helium and the refrigerant is cooled to a very low temperature by a refrigerator.

In FIG. 1, reference numeral 1 denotes a container, and a cross section having a columnar space 2 in the center is formed in an annular cylindrical body. A first shield 3 having a similar shape to the container 1 is sealed in the container 1, and a first shield 3 is provided in the first shield 3.
A second shield 4 having a similar shape to the shield 3 is enclosed. Further, the second shield 4 is provided inside the second shield 4.
And a liquid helium container 5 having a supply / discharge port 6 is sealed therein. And the liquid helium container 5
Inside, a cylindrical superconducting magnet (hereinafter simply referred to as a magnet) 7 is sealed. Liquid helium container 5
The second shield 4 and the first shield 3
One end of a supply / discharge pipe 8 penetrating the container 1 and protruding to the outside is attached. On the other hand, a valve 9 is attached to the other end of the supply / discharge pipe 8. Thus, the magnet 7
Is immersed in the liquid helium introduced into the liquid helium container 5 via the valve 9 and the supply / discharge pipe 8.
The helium gas formed by evaporating the liquid helium is discharged to the outside via the supply / discharge pipe 8 and the valve 9.

On the outer peripheral wall of the container 1, a cryogenic refrigerator is provided.
A first heat station 11 and a second heat station 12 (hereinafter simply referred to as a refrigerator) are mounted so as to protrude into the container 1. The outer peripheral wall of the first shield 3 is attached to the first heat station 11, and the second shield 4 is attached to the second heat station 12.
Outer peripheral wall is attached. Here, the container 1 is installed in a shield 13 that shields external noise.

On the other hand, a compressor unit 15
Is installed to supply the high-pressure refrigerant gas compressed by the compressor 16 to the refrigerator 10, while collecting the low-pressure refrigerant gas discharged from the refrigerator 10 into the compressor 16. The inverter 17 provided in the compressor unit 15 is connected to the refrigerator 10
Frequency modulation of an AC voltage supplied to a valve motor (not shown) for driving
To control the refrigeration capacity of the refrigerator 10 in a stepless manner. The noise filter 18
Is installed on the boundary wall of the shield 13 and the inverter 1
High frequency noise superimposed on the voltage from 7 to the valve motor is cut.

As described above, in the present embodiment,
An inverter 17 is provided in the compressor unit 15 of the refrigerator 10. The frequency-modulated voltage from the inverter 17 is supplied to the valve motor of the refrigerator 10 for cooling the magnet 7 in the shield 13 via the noise filter 18. Therefore, high-frequency noise superimposed on the voltage from inverter 17 is reduced by noise filter 1.
8 to remove. Therefore, according to the present embodiment, the rotation frequency of the valve motor of the refrigerator 10 can be steplessly controlled with a low noise frequency modulation voltage, and the refrigerating capacity of the refrigerator 10 can be steplessly controlled with high accuracy. Can be provided.

As described above, since the inverter is a source of high-frequency noise, a large-sized noise filter is required to cut high-frequency noise by the noise filter 18 alone. Hang on. Also, shield 13 via earth (GND)
No countermeasures are taken against transmission noise coming back from the side. Therefore, in the following second embodiment, an inexpensive cryogenic refrigerator that does not require a large-sized noise filter will be described.

FIG. 2 is a configuration diagram of a superconducting magnet cooling device using the cryogenic refrigerator according to the second embodiment. This superconducting magnet cooling device is of a direct cooling type, in which a superconducting magnet is directly cooled to a very low temperature by a refrigerator.

In FIG. 2, reference numeral 31 denotes a container, and a cross section having a cylindrical space 32 at the center is formed in an annular cylindrical body. A shield 33 having a similar shape to the container 31 is sealed in the container 31, and a cylindrical superconducting magnet (hereinafter simply referred to as a magnet) 34 is sealed in the shield 33.

A cryogenic refrigerator is provided on the outer peripheral wall of the container 31.
A first heat station 36 and a second heat station 37 are attached to the container 31 so as to protrude into the container 31. An outer peripheral wall of the shield 33 is attached to the first heat station 36, and a magnet 34 is attached to the second heat station 37.
Is attached to the outer peripheral surface. Here, the container 31
It is installed in a shield 38 that shields external noise.

On the other hand, in the machine room 39, a compressor unit 40
Is installed to supply the high-pressure refrigerant gas compressed by the compressor 41 to the refrigerator 35, while collecting the low-pressure refrigerant gas discharged from the refrigerator 35 into the compressor 41. The inverter 42 provided in the compressor unit 40 includes a refrigerator 35
The AC voltage supplied to the valve motor (not shown) is frequency-modulated and supplied through the power line 44 via the noise filter 43 to continuously control the refrigeration capacity of the refrigerator 35.

Here, the noise filter 43 in the present embodiment comprises a simple filter 45 and an insulating transformer 46.
And is installed on the boundary wall of the shield 38. Most of the high-frequency noise superimposed on the voltage from the inverter 42 to the valve motor is cut by the simple filter 45. Then, sudden noise and the like that cannot be completely cut by the simple filter 45 are removed by the insulating transformer 4.
Cut off at 6. In addition, by using the insulating transformer 46, the ground (GN
The transmission noise backing from the shield 38 via D) can also be cut.

As described above, in the present embodiment,
An insulating transformer 46 is added to the components of the noise filter 43. Therefore, the use of the simple filter 45 is enabled, and high-frequency noise can be cut at low cost. Also, the use of the isolation transformer 46 allows the
The transmission noise from the shield 38 side via (GND) can also be cut.

In each of the above embodiments, the case where the present invention is applied to a superconducting magnet cooling device is described as an example, but the present invention is not limited to this. For example, 3
The present invention is applicable to all devices that cool an object to a cryogenic temperature of 0K or less. In each of the above embodiments, the inverters 17 and 42 are used as power sources for supplying the modulated power.
However, the same effect can be obtained with a pulse frequency generator in which the valve motor of the refrigerator is a stepping motor.

[0024]

As is apparent from the above description, the cryogenic refrigeration apparatus according to the first aspect of the present invention comprises a power supply for supplying modulated power to a valve motor of an expansion refrigerator and the valve motor. Since the noise filter is provided, the intrusion of high-frequency noise from the power source into the refrigerator can be cut by the noise filter. Therefore, the refrigerating capacity of the refrigerator can be steplessly controlled with the reduced noise power, and a low-noise, high-performance cryogenic refrigerator can be provided.

In the cryogenic refrigeration apparatus according to the second aspect of the present invention, a simple noise filter and an insulating transformer are provided between the power source for supplying the modulated power to the valve motor of the expansion refrigerator and the valve motor. Because of the interposition, the intrusion of high-frequency noise from the power source into the refrigerator can be cut by an inexpensive simple noise filter, and noise that is not cut by the simple filter, such as sudden noise, can be cut by an insulating transformer. Further, transmission noise returning from the refrigerator side via the ground can be cut by the insulating transformer. Therefore, the refrigerating capacity of the refrigerator can be steplessly controlled with electric power with further reduced noise, and a low-noise, high-performance cryogenic refrigerator can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a cryogenic refrigeration apparatus of the present invention.

FIG. 2 is a configuration diagram of a cryogenic refrigeration apparatus different from FIG.

[Explanation of symbols]

10, 35 ... refrigerator, 13, 38 ... shield, 15, 40 ... compressor unit, 16, 41
... compressor, 17, 42 ... inverter, 18,
43: noise filter, 45: simple filter,
46 ... Insulation transformer.

Claims (2)

[Claims] A refrigerator (10) that switches and connects a refrigerant gas expansion chamber to a high pressure side and a low pressure side of a compressor (16) by a valve.
A cryogenic refrigeration apparatus having: a valve motor for driving the valve; and a power source (1) for supplying modulated power to the valve motor.
7) and a noise filter (18) provided between the power source (17) and the valve motor. 2. A refrigerator (35) for switching a refrigerant gas expansion chamber between a high pressure side and a low pressure side of a compressor (41) by a valve.
A cryogenic refrigeration system comprising: a valve motor for driving the valve; and a power source (4) for supplying modulated power to the valve motor.
(2) A cryogenic refrigeration apparatus comprising: a simple noise filter (45) and an insulating transformer (46) interposed between the power source (42) and the valve motor.