Magnetic measuring apparatus with sensor guide device and method for installing sensors therein

Apparatus for measuring weak magnetic fields includes a cryogenic vessel CR having a domed bottom D for accepting a human head, a plurality of magnetic sensor units 10 mounted upright on the inner surface of the bottom D of the cryogenic vessel CR, an interface device 20 for receiving output signals of the magnetic sensor units 10 through respective lead lines 4, a data processor device 30 for analyzing the output signals of the magnetic sensor units 10 to specify magnetic fields spread in the ambient space about the human head and calculating the activity of a brain B from the magnetic fields, and a display device 40 for displaying the brain activity. Each of the magnetic sensor units 10 is fed along its guide line G through a small opening OP of the cryogenic vessel CR and mounted upright on the bottom D. As the opening OP of the cryogenic vessel CR is relatively small, the evaporation loss of a coolant in the cryogenic vessel CR is minimized and the running cost of the apparatus will be decreased.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic measuring apparatus and more 
specifically, to a magnetic measuring apparatus appropriate for measuring 
magnetic fields spread in an ambient space about a head (brain), a chest 
(heart, stomach), an abdomen (liver), a fetus, and so on. 
FIG. 33 shows a prior art (U.S. Pat. No. 5,475,306) magnetic measuring 
apparatus for measuring magnetic fields spread in the ambient space about 
a human bead. 
The magnetic measuring apparatus 500 comprises a cryogenic vessel CR' 
composed of an inner vessel CRI' and an outer vessel CRO having a domed 
bottom D for accepting the human head, a lid LD' for closing an opening 
OP' provided in the top of the cryogenic vessel CR', a multiplicity of 
magnetic sensor units 50 suspended by pipes PP respectively from the lid 
LD' so as to be seated directly on the upper surface of the domed bottom 
D, signal lines 4 for transmission of output signals from their respective 
magnetic sensor units 50, an interface device 20 connected to the signal 
lines 4, a data processor device 30 for analyzing the output signals of 
the magnetic sensor units 50 to specify magnetic fields spread in the 
ambient space about the head and calculating activity data of a brain B 
from the magnetic fields, and a display device 40 for displaying the 
calculated activity data. 
The space between the inner vessel CSI' and the outer vessel CRO is filled 
with a thermal insulating material Dn and air is evacuated therefrom. 
Denoted by PA is a packing made of e.g. rubber. 
A coolant feed/exhaust double tube ST is provided for feeding to and 
exhausting a coolant from the cryogenic vessel CR'. The coolant may be a 
liquid helium (4.2K). 
As the prior art magnetic measuring apparatus 500 shown in FIG. 33 has the 
magnetic sensor units 50 mounted in a suspended arrangement, the opening 
OP' is formed substantially equal in size to the cross section of a human 
head. 
But when the opening OP' is considerably large (over 10 cm in diameter), it 
causes a problem of passing of much heat thus increasing the evaporation 
loss of the coolant and the cost of running. 
In addition, there is another problem that the cryogenic vessel CR' cannot 
have an overhand reducing the opening OP' because the magnetic sensor 
units 50 are vertically suspended from the lid LD'. 
Furthermore, there is the other problem that the domed bottom D of the 
magnetic measuring apparatus 500 accepts the head of one single test 
object at a time, thus throughput cannot be increased. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a magnetic 
measuring apparatus which can reduce the evaporation loss of a coolant and 
allows a cryogenic vessel to have an overhang configuration where the 
magnetic sensors are mounted beneath the overhang. 
It is a secondary object of the present invention to provide a magnetic 
measuring apparatus capable of accepting a plurality of test objects at a 
time and increasing the throughput. 
For embodying a first feature of the present invention, a measuring 
apparatus having a plurality of magnetic sensors installed in a cryogenic 
vessel, signal lines of the magnetic sensors arranged extending out from 
an opening provided in the top of the cryogenic vessel, a coolant filled 
in the cryogenic vessel, and a lid closing the opening is provided 
comprising magnetic sensor holders mounted on a bottom or side of the 
cryogenic vessel for accepting and holding their respective magnetic 
sensors, and guide lines joined at a first end to the magnetic sensor 
holders respectively or their proximities and having a second end 
extending out from the opening of the cryogenic vessel so that the 
magnetic sensor is fed and moved from the opening to the corresponding 
magnetic sensor holder along the guide line. 
The bottom or side of the cryogenic vessel may be flat shaped but is 
preferably formed to an arcuate configuration for matching the shape of a 
test object. More specifically, the arcuate configuration is a helmet-like 
shape for accepting a human head or a body-like shape for a human body. 
The magnetic measuring apparatus according to the first feature of the 
present invention permits the magnetic sensors to be fed and moved along 
their respective guide lines from the opening to the corresponding 
magnetic sensor holders for installation on the bottom or side of the 
cryogenic vessel. Hence, the opening of the cryogenic vessel is minimized 
in size (having a diameter of less than 5 cm) to pass one magnetic sensor 
together with the signal lines and the evaporation loss of the coolant 
will significantly be decreased. Also, it is possible to form an undercut 
portion beneath an overhand of the cryogenic vessel where the magnetic 
sensors are installed without difficulty. 
For embodying a second feature of the present invention, a magnetic 
measuring apparatus having a plurality of magnetic sensors installed in a 
cryogenic vessel, signal lines of the magnetic sensors arranged extending 
out from an opening provided in the top of the cryogenic vessel, a coolant 
filled in the cryogenic vessel, and a lid closing the opening is provided 
comprising magnetic sensor holders mounted on a bottom or side of the 
cryogenic vessel for accepting and holding their respective magnetic 
sensors, and guide lines joined at first end to the magnetic sensor 
holders respectively or their proximities and having a second end 
extending out or enabled to be withdrawn from the opening of the cryogenic 
vessel so that the magnetic sensor is fed and moved from the opening to 
the corresponding magnetic sensor holder along the guide line and 
withdrawn from the corresponding magnetic sensor holder to the opening 
along the same. 
Similarly, the magnetic measuring apparatus according to the second feature 
of the present invention permits the magnetic sensors to be fed and moved 
along their respective guide lines from the opening to the corresponding 
magnetic sensor holders for installation on the bottom or side of the 
cryogenic vessel. Hence, the opening of the cryogenic vessel is minimized 
in size (having a diameter of less than 5 cm) to pass one magnetic sensor 
together with the signal lines and the evaporation loss of the coolant 
will significantly be decreased. Also, it is possible to form an undercut 
portion beneath an overhang of the cryogenic vessel where the magnetic 
sensors are installed without difficulty. 
In addition, any of the magnetic sensors can be withdrawn from the opening 
along the corresponding guide line which has been pulled out with its 
second end. As the result, replacement or repair of the magnetic sensors 
will be carried out with much ease. 
For embodying a third feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the 
magnetic sensor is integrated with a pipe body having a through hole 
through which the guide line is passed. 
The magnetic measuring apparatus according to the third feature of the 
present invention allows the magnetic sensor to be fed and moved from the 
opening to the corresponding magnetic sensor holder along the guide line 
which passes through the through hole of the pipe body of the magnetic 
sensor. This will facilitate the installation of the magnetic sensors on 
the domed or arcuate region of the cryogenic vessel and even on an 
undercut portion formed beneath an overhang defining the opening. 
For embodying a fourth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the 
magnetic sensor holder comprises a support base secured to the bottom or 
side of the cryogenic vessel for holding the corresponding magnetic sensor 
as fitted into the through hole of the pipe body, and a flexible guide 
member extending from the support base. 
The magnetic measuring apparatus according to the fourth feature of the 
present invention allows the pipe body of each magnetic sensor to be fed 
along the flexible guide member without jerky movement and fitted onto the 
magnetic sensor support securely. As their pipe bodies are smoothly moved 
to the corresponding magnetic sensor supports, the magnetic sensors are 
accurately located on the bottom or side of the cryogenic vessel and even 
on an undercut portion of an overhang defining the opening. 
For embodying a fifth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the 
support base of the magnetic sensor holder comprises a first support base 
secured to the bottom or side of the cryogenic vessel and a second support 
base pivotably mounted to the first support base. 
The magnetic measuring apparatus according to the fifth feature of the 
present invention permits the second support base to be pivoted on the 
first support base. Hence, the pipe body of the magnetic sensor is readily 
fitted onto the support base without jerky movement. 
For embodying a sixth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the guide 
line is an elastic tube arranged for expansion and retraction in radial 
directions so that the first end of the tube guide line is fitted onto the 
guide member of the magnetic sensor holder. 
The magnetic measuring apparatus according to the sixth feature of the 
present invention allows the first end of the guide line made of the 
elastic tube to be elastically fitted onto the guide member of the 
magnetic sensor holder. Hence the joining of the guide lines to their 
respective magnetic sensor holders will be conducted at a higher 
efficiency. 
For embodying a seventh feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which each 
magnetic sensor is substantially joined to a first end of a pullup line 
which has a second end extending out or enabled to be withdrawn from the 
opening of the cryogenic vessel. 
The magnetic measuring apparatus according to the seventh feature of the 
present invention allows the second end of the pullup line to be withdrawn 
from the opening so that when the pullup line is pulled, its joined 
magnetic sensor is withdrawn, hence contributing to the ease of 
replacement or repair of any of the magnetic sensors. 
For embodying an eighth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the 
magnetic sensor is integrated with a pipe body having a through hole 
through which the guide line is passed and joined to the first end of the 
pullup line. 
The magnetic measuring apparatus according to the eighth feature of the 
present invention permits the magnetic sensor to be fed and moved along 
the guide line from the opening to the corresponding magnetic sensor 
holder with the through hole of its pipe body engaged with the guide line. 
Hence, the installation of the magnetic sensors on the bottom or side of 
the cryogenic vessel will be facilitated. Also, when the second end of the 
pullup line is pulled up, its joined magnetic sensor will readily be 
removed. As the result, replacement or repair of any of the magnetic 
sensors will be conducted at a higher efficiency. 
For embodying a ninth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the pipe 
body of the magnetic sensor is arranged so that it is split and removed 
from the magnetic sensor holder when the pullup line is pulled. 
The magnetic measuring apparatus according to the ninth feature of the 
present invention allows the pipe body of the magnetic sensor to be split 
upon being pulled, hence facilitating the removal of the magnetic sensor 
from its magnetic sensor holder. 
For embodying a tenth feature of the present invention, a magnetic 
measuring apparatus of the prescribed type is provided in which the bottom 
or side of the cryogenic vessel is formed to have two or more groups of 
the magnetic sensor holders at plural measuring areas so that plural test 
objects can simultaneously be placed in the measuring areas of the 
magnetic sensors of the groups of the magnetic sensor holders. 
The magnetic measuring apparatus according to the tenth feature of the 
present invention allows the plural test objects to be simultaneously 
located in the measuring areas of the magnetic sensors of the groups, thus 
increasing the throughput. When a domed or arcuate region is formed on the 
side of the cryogenic vessel, it includes an undercut beneath an overhang 
at defining the opening of the cryogenic vessel. The magnetic sensors arc 
mounted on the undercut portion without difficulty. 
For embodying an eleventh feature of the present invention, a magnetic 
measuring apparatus having a plurality of magnetic sensors installed in a 
cryogenic vessel, signal lines of the magnetic sensors arranged extending 
out from an opening provided in the top of the cryogenic vessel, a coolant 
filled in the cryogenic vessel, and a lid closing the opening is provided 
further comprising two or more groups of magnetic sensor holders mounted 
on a bottom or side of the cryogenic vessel at plural measuring areas for 
allowing plural test objects to be simultaneously taken in the measuring 
areas of the magnetic sensors of the groups of the magnetic sensor 
holders. 
The measuring apparatus according to the eleventh feature of the present 
invention allows the plural test objects to be simultaneously located in 
the measuring areas of the magnetic sensors of the groups, thus increasing 
the throughput.

DETAILED DESCRIPTION OF THE INVENTION 
The embodiments of the present invention will be described in more details 
referring to the accompanying drawings. Although the following description 
involves measurement of magnetic fields spread in the ambient space about 
a human head, the same about a chest, an abdomen, a fetus, or any other 
like object can be measured with equal success. 
FIG. 1 is a schematic view of a magnetic measuring apparatus showing a 
first embodiment of the present invention. 
The magnetic measuring apparatus 100 comprises a cryogenic Dewar vessel CR 
composed of an inner vessel CRI and an outer vessel CRO having a domed 
bottom D for accepting a human head, a multiplicity of magnetic sensor 
units 10 mounted upright on an inner surface of the domed bottom D of the 
cryogenic vessel CR, an interface device 20 for receiving output signals 
from respective magnetic sensor units 10 through signal lines 4, a data 
processor device 30 for analyzing the output signals of the magnetic 
sensor units 10 to specify magnetic fields spread in the ambient space 
about the head and calculating activity data of a brain B from the 
magnetic fields, and a display device 40 for displaying the calculated 
activity data. 
The space between the inner vessel CRI and the outer vessel CRO is filled 
with a thermal insulating material Dn and air is evacuated therefrom. 
There are also provided guide lines G, pullup lines P, a ring R1 for 
bundling the guide lines G and the pullup lines P, a master cable M, and 
another ring R2 connected to one end of the master cable M. 
The cryogenic vessel CR has a relatively small opening OP provided in a top 
thereof which overhangs the magnetic sensor units 10. Through the opening 
OP, the magnetic sensor units 10 are inserted and mounted upright on the 
inner surface of the domed bottom D of the inner vessel CRI. The opening 
OP also allows the signal lines 4 and the master cable M from the magnetic 
sensor units 10 to extend to the outside therethrough. The opening OP is 
closed with a combination of a lid LD and a packing PA. A coolant 
feed/exhaust double tube ST is provided through the lid LD for feeding a 
coolant to the cryogenic vessel CR. For replacement or repair, the 
magnetic sensor units 10 can be dismounted and mounted through the opening 
OP. 
The packing PA may be made of a rubber material and the coolant may be a 
liquid helium (4.2K). 
A procedure of manufacturing the magnetic measurement apparatus 100 will be 
explained referring to FIG. 2 to FIG. 12. 
The procedure starts with forming a bottom part CRIb of the inner vessel 
CRI as shown in FIG. 2. A given number (for example, 16 to 150) of 
magnetic sensor holders H are mounted on an arcuate region of the domed 
bottom D. The magnetic sensor holder H comprises a support base SB mounted 
upright on the bottom D and a flexible guide GB extending upwardly from 
the support base SB. 
As shown in FIG. 3, the support base SB is made of preferably a nylon 
material having a cylindrical shape of 95 mm in length and 8 mm in 
diameter. A bulged region BB, of which a diameter is preferably 10.5 mm, 
is formed near a base end of the support base SB. 
The guide GB is made of preferably a nylon material having a whisker-like 
shape of 50 mm in length and 3 mm in diameter and arranged to curve 
upwardly. 
Each of guide lines G is then joined at one end to the corresponding 
magnetic sensor holder H, as shown in FIG. 4. The guide line G is 
preferably a flexible tube fabricated by knitting nylon yarns so that its 
diameter can vary from 1 mm to 15 mm. A first tube end of the guide line G 
is fitted over the guide GB and an upper portion of the support base SB. 
This is followed by forming a side Q of the inner vessel CRI, as shown in 
FIG. 5. As the result, the entirety of the inner vessel CRI is completed 
with the relatively small opening OP in the top thereof. Simultaneously, 
the second end of the guide line G, of which the first end is joined to 
the magnetic sensor holder H, is withdrawn through the opening OP. 
The diameter of the small opening OP is preferably 3 cm to 5 cm. A neck 
region NK of the inner vessel CRI has a same diameter as the opening OP 
and a depth of about 30 cm to 50 cm. 
Then, the thermal insulating material Dn is installed around the inner 
vessel CRI and the outer vessel CRO is mounted to complete the cryogenic 
vessel CR with the small opening OP, as shown in FIG. 6. 
This is followed by preparing the magnetic sensor units 10, one of which 
being shown in FIG. 7. 
The magnetic sensor unit 10 is fabricated by mounting a magnetic sensor 
(not shown), such as a superconductive quantum interference device, and an 
electronic circuit 3 to a pipe member 1 having a through hole 2 therein 
and joining the signal line 4 to the electronic circuit 3 and the pullup 
line P to the pipe member 1. 
The pipe member 1 is preferably an epoxy resin tubing having a length of 
100 mm, an outer diameter of 20 mm, and an inner diameter of 10 mm. 
The pullup line P is preferably a nylon string. 
As shown in FIGS. 8 and 9, each of the guide lines G is passed through the 
through hole 2 of the corresponding magnetic sensor unit 10. 
The magnetic sensor unit 10 is then lowered and fitted on to the support 
base SB of the magnetic sensor holder H by means of a pressing jig R such 
as a coil spring as shown in FIGS. 10 and 11 or plastic tube. As the 
through hole 2 of the magnetic sensor unit 10 is 10 mm in diameter and the 
bulged portion BB of the support base SB is 10.5 mm in outer diameter, the 
magnetic sensor unit 10 is securely anchored to the support base SB. The 
pressing jig R is then removed out as shown in FIG. 12. 
This is followed by placing the guide lines G and the pullup lines P in the 
ring R1 and connecting the ring R1 to one end of the master cable M as 
shown in FIG. 1. The ring R1 is then dropped from the small opening OP 
into the cryogenic vessel CR and the other end of the master cable M is 
joined to the ring R2 which is held outside the cryogenic vessel CR. 
Finally, the opening OP is closed with the lid LD and the packing PA and 
the coolant is supplied via the coolant feed/exhaust double tube ST to 
fill the cryogenic vessel CR. 
For replacement or repairing any of the magnetic sensor units 10, the ring 
R2 is pulled upwardly to withdraw the ring R1 joined to the master cable 
M. When the guide line G and the pullup line P of the target magnetic 
sensor unit 10 are selected, the magnetic sensor unit 10 is removed out 
through the opening OP by pulling the pullup line P. 
Accordingly, the magnetic measuring apparatus 100 has the relatively small 
opening OP which allows the entering of a minimum of heat and thus 
minimizes the evaporation loss of the coolant in the cryogenic vessel CR 
contributing to the lower running cost. 
The present invention provides a second embodiment where the magnetic 
sensor unit 10 is replaced by another magnetic sensor unit 10a illustrated 
in FIG. 13. 
The magnetic sensor unit 10a includes a pipe member 1a of a square tube 
configuration. 
The present invention provides a third embodiment where the magnetic sensor 
unit 10 is replaced by a further magnetic sensor unit 10b shown in FIG. 
14. 
The magnetic sensor unit 10b includes a block member 1b provided with a 
pipe 6 through which the guide line G is passed. 
FIG. 15 is a schematic view of a magnetic measuring apparatus showing a 
fourth embodiment of the present invention. 
The magnetic measuring apparatus 200 has a bottom D' of an inner vessel CRI 
and a bottom of an outer vessel CRO of a cryogenic vessel CR formed for 
accepting a human head up to its rear lower end. The other components and 
their arrangement are the same as those of the magnetic measuring 
apparatus 100 of the first embodiment. 
A rear lower end region of the bottom D' is shaped into an undercut where a 
magnetic sensor unit 10' is allocated to a region tilted below the 
horizontal line. However, due to respective guide line G, the magnetic 
sensor unit 10' can readily be installed with ease. For replacement or 
repair, the magnetic sensor unit 10' is easily removed. 
FIG. 16 is a schematic view of a magnetic measuring apparatus showing a 
fifth embodiment of the present invention. 
The magnetic measuring apparatus 300 has a cryogenic vessel CR composed of 
an inner vessel CRI and an outer vessel CRO having two domed regions S1 
and S2 at opposite sides for accepting human heads respectively. Groups of 
the magnetic sensor units 10 and 10' are mounted upright on the inner 
surfaces of the domed regions S1 and S2. The other components and their 
arrangement are identical to those of the magnetic measuring apparatus 100 
of the first embodiment. 
As shown, the magnetic sensor units 10' are mounted nearly upside down. 
However, due to their respective guide lines G, the magnetic sensor units 
10' can readily be installed without difficulty. For replacement or 
repair, the magnetic sensor units 10' are removed with ease. 
A data processor device 30 is provided for parallel processing the output 
signals from the magnetic sensor units 10 of one group on the domed region 
S1 and of the other group on the domed region S2. This allows two test 
objects to be simultaneously measured for the magnetic fields. 
If desired, three or more of the domed regions may be provided. 
The present invention provides a sixth embodiment where the magnetic sensor 
holder H is replaces by another magnetic sensor holder H1 shown in FIG. 
17(a) and (b). 
As apparent from FIG. 17(a), the magnetic sensor holder H1 comprises a 
first support base SB1 having a ball holding pit BH therein and mounted 
upright to the domed bottom D, a second support base SB2 having a ball BL 
thereof accommodated in the ball holding pit BH, and a flexible guide GB 
extending outwardly from the second support base SB2. 
The second support base SB2 is hence pivotable on the ball BL as shown in 
FIG. 17(b). 
As shown in FIG. 18, the magnetic sensor holder H1 is joined to a first end 
of the guide line G. The first end of the guide line G is fitted over the 
flexible guide GB onto the first support base SB1. 
As its second support base SB2 of the magnetic sensor holder H1 is 
pivotable, the magnetic sensor unit H1 allows the corresponding magnetic 
sensor unit 10 or 10' to be smoothly fitted thereonto without jerking 
movements on the way. 
The present invention provides a seventh embodiment where the magnetic 
sensor unit 10 is replaced by a still further magnetic sensor unit 10c 
illustrated in FIG. 19(a) and (b). 
As best shown in FIG. 19(a), the magnetic sensor unit 10c includes a pipe 
member 1c having slits CK therein. Two branches of the pullup line P are 
joined to both segments of the pipe member 1c defined by the slits CK. 
In action, when the pullup line P is pulled in the direction denoted by the 
arrow "a" of FIG. 19(b), the pipe member 1c is separated into the two 
segments 1d and 1e along the slits CK so that the magnetic sensor unit 10c 
is easily removed from the corresponding magnetic sensor holder H. 
FIG. 20 is a schematic view of a magnetic measuring apparatus showing an 
eighth embodiment of the present invention. 
The magnetic measuring apparatus 400 includes guide line mounts GT mounted 
adjacent to their respective sensor units 10 upright on the bottom D of 
the inner vessel CRI of the cryogenic vessel CR. The guide line mount GT 
is joined to a first end of the guide line G. No pullup line is joined to 
the magnetic sensor unit 10. The other components and their arrangement 
are identical to those of the magnetic measuring apparatus 100 of the 
first embodiment. 
A procedure of fabricating the magnetic measuring apparatus 400 will now be 
explained referring to FIG. 21 to FIG. 32. 
The procedure starts with forming a bottom part CRIb of the inner vessel 
CRI and mounting a plurality of magnetic sensor holders H2 on a domed 
region of the bottom D, as shown in FIG. 21. The guide line mounts GT are 
then installed adjacent to their respective magnetic sensor holders H2. 
The magnetic sensor holder H2 may be a nylon cylinder of 95 mm in length 
and 8 mm in diameter, configured as shown in FIG. 22. The magnetic sensor 
holder H2 has a bulged region BB near a base end thereof having diameter 
that is preferably 10.5 mm. 
The guide line mount GT is preferably a nylon cylinder of 25 mm in length 
and 4 mm in diameter. 
As shown in FIG. 23, the first end of the guide line G is joined to the 
guide line mount GT. The guide line G is preferably a tube made by 
knitting nylon yarns so that its diameter can vary from 1 mm to 15 mm. The 
first end of the tube guide line G is fitted onto the corresponding guide 
line mount GT. 
This is followed by adding a side Q of the inner vessel CRI thus to form 
the entirety of the inner vessel CRI having a relatively small opening OP 
on the top, as shown in FIG. 24. At that time, the second ends of the 
guide lines G, connected at their first ends to the corresponding magnetic 
sensor holders H2, are exposed out through the opening OP. 
The relatively small opening OP is preferably 3 cm to 5 cm in diameter. A 
neck region NK of the inner vessel CRI is provided of which an inner 
diameter is identical to that of the opening OP and extends downwardly 
about 30 cm to 50 cm. 
Then, a thermal insulating material Dn is positioned as shown and an outer 
vessel CRO is added thus forming the cryogenic vessel CR with the opening 
OP, as shown in FIG. 25. 
This is followed by preparing a sensor mounting jig 60 shown in FIG. 26. 
The sensor mounting jig 60 comprises a tube 61 having a through hole 61a 
therein, a tube holding handle 62 joined to a first end of the tube 61, a 
plurality of rings 63 mounted on an outer periphery of the tube 61, a wire 
64 joined at a first end to a handle 66 and extending through the through 
hole 61a of the tube 61, and a gripper 65 joined to a second end of the 
wire 64. 
When the tube holding handle 62 is pulled relative to the handle 66 being 
held stationary, the gripper 65 is exposed out from the through hole 61a 
and opens. 
When the tube holding handle 62 is pushed in the direction denoted by the 
arrow b in FIG. 27 relative to the handle 66 being held stationary, the 
gripper 65 is retracted into the through hole 61a and closes. 
This closing and opening action allows the gripper 65 to hold and release 
the magnetic sensor unit 10. 
The guide line G is then passed through the rings 63 of the sensor mounting 
jig 60 as shown in FIG. 28 while the gripper 65 of the sensor mounting jig 
60 holds the magnetic sensor unit 10. 
As the tube holding handle 62 and the handle 66 are moved forward, the 
magnetic sensor unit 10 held by the gripper 65 travels along the guide 
line G towards the magnetic sensor holder H2 as shown in FIG. 29. 
When the tube holding handle 62 and the handle 66 have been pressed down, 
the magnetic sensor unit 10 held by the gripper 65 is fitted onto the 
magnetic sensor holder H2 as shown in FIG. 30. Because the diameter of a 
through hole 2 of the magnetic sensor unit 10 is 10 mm and the bulged 
region BB of the magnetic sensor holder H2 is 10.5 mm, the magnetic sensor 
unit 10 is tightly secured to the magnetic sensor holder H2. 
This action may preferably be carried out using a fiber scope. 
Then, the magnetic sensor unit 10 is released from the gripper 65 as shown 
in FIG. 31. 
The sensor mounting jig 60 is removed from the guide line G by pulling the 
tube holding handle 62 and the handle 66, as shown in FIG. 32. 
Similarly, the other magnetic sensor units 10 are mounted to their 
corresponding magnetic sensor holders H2. 
This is followed by bundling all the guide lines G with a ring R1, joining 
the ring R1 to the first end of a master cable M, dropping the ring R1 
through the opening OP into the interior of the cryogenic vessel CR, 
joining the second end of the master cable M to a ring R2, and holding the 
ring R2 outside the cryogenic vessel CR. 
Finally, the opening OP is closed with a lid LD and a packing PA and the 
cryogenic vessel CR is filled with a coolant supplied via a coolant 
feed/exhaust double tube ST. 
For replacement or repair of any of the magnetic sensor units 10, the ring 
R2 is pulled to withdraw the ring R1 joined to the first end of the master 
cable M allowing the corresponding guide line G joined to the required 
magnetic sensor unit 10 to be selected. The guide line G is passed through 
the rings 63 of the sensor mounting jig 60. As the sensor mounting jig 60 
has been moved in, its gripper 65 holds and withdraws the magnetic sensor 
unit 10. 
Accordingly the magnetic measuring apparatus 400 has the relatively small 
opening OP hence allowing the entry of minimum amounts of heat and 
reducing the evaporation loss of the coolant in the cryogenic vessel CR 
and thus contributing to the lower running cost. 
The magnetic measuring apparatus of the present invention allows the 
magnetic sensors to be readily installed in the cryogenic vessel through 
its relatively small opening and any of them to be dismounted for 
replacement or repair without difficulty. As the relatively small opening 
permits the passing of a minimum amount of heat and decreases the 
evaporation loss of a coolant, the running cost will considerably be 
reduced. Since the magnetic sensors are mounted to any configuration, an 
undercut portion of the cryogenic vessel is applicable for matching the 
shape of a test object. This also permits a specific construction for 
accepting two or more test objects and will thus contribute to the higher 
throughput of the magnetic measuring apparatus.