Measuring fixture

An accurately formed straight edge member serves as a track for a carriage movable along the length of an elongated component. Distance measuring devices supported by the carriage engage the adjacent surface of the component by which flatness, bow and twist of the component can be determined.

BACKGROUND 
There are numerous components in industrial and utility installations which 
require on-site, pre-service inspection and/or periodic in-service 
inspection to verify continued serviceability. Such inspection frequently 
includes dimensional measurements. A notable example is the on-site 
inspection of components of a nuclear reactor, especially replaceable 
components such as control rods, fuel elements and fuel channels. 
For example, a typical fuel assembly having a removable and reusable flow 
channel is shown in U.S. Pat. No. 3,689,358. Such an elongated square 
tubular fuel channel may be in the order of 13 cm in transverse cross 
section dimensions and in the order of 4 m in length. It is necessary to 
assure that the four major surfaces of such channels are sufficiently flat 
so as not to interfere with the insertion of control rods between fuel 
assemblies during operation in the nuclear reactor core. Dimensional 
tolerances over the length of such a channel may be in the order of 0.127 
mm. To perform the necessary flatness measurement of such a component, an 
elongated accurate and stable measuring fixture is required. 
Since flow channels, and other reactor components, which have been 
subjected to reactor service are radioactive, it is necessary that the 
measuring device be remotely operable under water to protect the equipment 
operators from radiation. It is desirable that the measuring device be 
sufficiently portable for repositioning within a water pool, for movement 
from one pool to another, and for removal to dry storage when not in use. 
Thus an object of the invention is a portable device or fixture for 
accurate dimensional measurement of radioactive components. 
SUMMARY 
The dimension measuring fixture of the invention comprises a vertically 
oriented, elongated, accurately formed straight edge member which serves 
as a plane of reference and as a track for an instrument bearing carriage. 
The straight edge member is rectangular in transverse cross section and, 
as a feature of the invention, it is formed with a series of relatively 
large holes along its longitudinal axis for enhanced heat distribution to 
minimize thermal deformation and to provide a high stiffness-to-weight 
ratio. 
The straight edge is supported by an elongated support beam such as an I 
beam, the straight edge being attached thereto by pivot pins at one end 
and a sliding spherical bearing at the other end whereby transmission of 
deforming loads is minimized. 
The flow channel, or component to be measured, is supported adjacent the 
straight edge by a bearing mounted support at the bottom end and an 
adjustable clamp arrangement at the top end. 
As the carriage is moved along the straight edge, measurement devices 
engage the channel, the measurement direction being such that thermal 
patterns are symmetrical to reduce thermally-induced-bow measurement 
errors and in the direction of maximum straight edge stiffness.

DESCRIPTION 
A measuring fixture 11 according to the invention is illustrated in FIG. 1 
as mounted in operating position along a wall 12 in a pool by water 13. 
The main frame of the fixture is an elongated support beam 14 shown herein 
as an H beam. 
An upper bracket 16, attached to the beam 14 near its upper end, includes a 
pair of rearwardly extending arms 17 formed to hook over a ledge 18 of the 
pool wall 12 to thereby support the fixture 11 in suspension along the 
wall 12. Adjustable pads 15 provide verticality adjustment. 
A lower bracket 19, attached to the beam 14 at its lower end, includes a 
pair of side plates 21. Rearward extensions 22 abut the wall 12 to 
position the beam 14 substantially parallel with the wall 12. Forward 
extensions 23 and a cross plate 24 provide support for other components of 
the fixture as described hereinafter. 
Supported between lower bracket 19 and an intermediate bracket 26 is a 
straight edge member 27 which serves as an accurate measurement plane of 
reference and as a track for an instrument bearing carriage 28. 
As best shown in FIG. 2, straight edge 27 is supported at its lower end by 
lower bracket 21 with a pair of pivot pins 29, and it is held in position 
at its upper end by intermediate bracket 26 with a center pin 31 carrying 
a sliding, spherical bearing journalled in a flange 32 of bracket 26. This 
mounting arrangement allows the straight edge 27 freedom of thermal 
expansion and contraction and aids in preventing transmission thereto of 
deforming loads from other portions of the fixture. To further minimize 
thermal deformation, the straight edge 27 is formed with a series of 
relatively large, equally spaced holes 33 along its length. 
To minimize torsional distortion of the support beam 14 that would affect 
the straight edge 27, the portion of beam 14 between intermediate bracket 
26 and the lower end of the beam is "boxed in" by a back plate 34 secured, 
as by welding, to the rear edges thereof. The part of the beam 14 above 
the intermediate bracket 26 is left unboxed. 
Thus any twisting of beam 14, as might occur for example from unevenness of 
the pool wall 12, takes place in the part of the beam above the 
intermediate bracket 26 whereby transmission of such deformation to the 
straight edge 27 is avoided. 
The component to be measured, shown in FIG. 1 in phantom view by dashed 
lines as a fuel assembly flow channel 36 is removably secured in a 
position generally parallel to the straight edge 27. The channel 36 is 
supported at its bottom end by a channel support member 37 and is 
positioned at its top end by a clamp arrangement 38 secured to the top end 
of straight edge 27. 
The clamp arrangement 38 includes a fixed arm 39 and a swinging arm 41, the 
swinging arm 41 being remotely operable by a hydraulic or pneumatic 
cylinder 40 in well-known manner. The fixed arm 39 is fitted with a pair 
of jack screws 42 for adjustment of the alignment of the top end of the 
channel with the plane of the tips of the measuring devices on carriage 
28. The channel contacting faces of the swinging arm 41 and the jack 
screws may be fitted with material such as nylon to prevent scratching of 
the channel. 
The channel is supported at its bottom end by channel support member 37, in 
a manner which does not restrain the channel from rotational motion about 
is longitudinal axis. This is necessary for measurement of channel twist. 
As shown in FIG. 3, this feature is provided by a support socket 43 which 
is journalled to allow rotational motion thereof by an annular ball 
bearing 44 carried by a bearing plate 46 secured to a spacing sleeve 47 
which, in turn, is secured to the cross plate 24 of the lower bracket 19. 
The subject measuring fixture is adapted to accommodate and measure empty 
channels or flow channels which are still mounted on fuel assemblies (as 
shown in previously mentioned U.S. Pat. No. 3,689,358). Therefore, the 
upper end of the bore of support socket 43 is appropriately shaped, as at 
48, to receive and mate with the nose pieces of the fuel assemblies to be 
accommodated. 
To accommodate empty flow channels, an empty channel adapter 49 is 
provided. The lower end 51 of the channel adapter has the shape of a fuel 
assembly nose piece for fitting into the support socket 43. The upper end 
52 of the channel adapter has a pyramid shape, or the like, for ease of 
fitting the square end of the empty channel thereover and the adapter is 
sized at 53 near the base of the pyramid portion to fix the position of 
the channel 36 on the channel adapter. 
It is noted that, as shown in FIG. 3, the cross plate 24 and the bearing 
plate 46 are formed with large holes 45 and 50, respectively, and the 
support socket 43 and the adapter 49 are formed with large through bores. 
This provides for water circulation through the component being measured 
which allows water that has become radioactive in the component to drain 
away thus reducing user exposure. It also provides a convection path to 
convey heat away from the measuring devices. 
Empty channels or fuel assemblies, as the case may be, can be placed in 
position or removed from the measuring fixture by any suitable lifting and 
maneuvering device such as an overhead or boom mounted hoist (not shown) 
which is typically available as an adjunct to a nuclear fuel storage pool. 
Such hoist arrangements are shown, for example, in copending patent 
application Ser. No. 747,824 filed Dec. 6, 1976, now U.S. Pat. No. 
4,172,760. 
Attention is now directed to the instrument carriage 28 shown in FIG. 1 and 
with greater clarity in FIG. 4. As illustrated herein the carriage 28 
which is mounted on the straight edge 27 by a system of rollers or wheels 
includes a T-shaped front plate 54 which serves as the main frame of the 
carriage. The front plate 54 is positioned with respect to and guided 
along the straight edge 27 by a plurality of guide rollers. These guide 
rollers include a first pair of spaced rollers 56(1) and 56(2) journalled 
to the T portion of plate 54 for engagement with the right-front face 
portion of straight edge 27, a second pair of spaced rollers 57 likewise 
journalled to the T portion of plate 54 but for engagement with the right 
side of straight edge 27, and a single roller 58 journalled near the left 
hand end of plate 54 for engagement with the left-front face portion of 
straight edge 27. A plurality of rollers 59 journalled in a stud-mounted, 
spring-loaded back plate 61 and a pair of rollers 62 journalled in a 
stud-mounted, spring-loaded side plate 63 provide pressure on the guide 
rollers and assure their engagement with straight edge 27. 
Secured to the right hand end of plate 54 is an arm 64 suitable for 
supporting a plurality of distance detectors or other measuring devices 
66(1)-66(3) in appropriate position for engagement with the flow channel 
36 to be measured. The devices 66(1)-66(3) may be, for example, linear 
variable differential transformers. Briefly, such a device comprises a 
linearly movable spring loaded plunger 67 extending from a housing. 
Movement of the plunger 67 changes the mutual inductance of a pair of 
coils within the housing. Thus the mutual inductance of the pair of coils 
can be measured and interpreted as a function of the linear position of 
the plunger. The plunger 67 is fitted at its outer end with a rounded, 
smooth-faced nose piece 69 for sliding engagement with the outer surface 
of the channel 36 to be measured. 
Suitable such distance detectors are available from Schaevitz Engineering, 
U.S. Route 130 and Union Avenue, Pennsauken, New Jersey as catalog item 
No. GCA-121-500-0624. 
The signals from detectors 66(1)-66(3) are transmitted via a cable 71 to a 
signal processing recording and display device 72 (FIG. 1). A suitable 
device 72 is available from Schaevitz Engineering as catalog item No. 
CAS-0653. 
To be noted is that the detectors 66(1)-66(3) are supported such that the 
direction of measurement is in the direction of the major cross section 
dimension of straight edge 27 and hence in the direction of maximum 
straight edge stiffness. 
As illustrated herein, the carriage 28 is manually movable along the length 
of straight edge 27 as follows: A roller chain 73 attached to the carriage 
28 is engaged by a lower idler sprocket wheel 74 and by an upper driven 
sprocket wheel 76. Wheel 76 is driven from a hand wheel 77 through 
suitable shafting and a pair of right-angle gear boxes 78(1) and 78(2). A 
counter 79 registers the rotations of the hand wheel 76 and can be 
designed to indicate the position of the carriage 28 along the straight 
edge 27 in convenient units. Also, a toothed wheel 82 engaged by a 
spring-loaded ball detent can be keyed to the shaft of hand wheel 77 to 
provide incremental carriage positioning and prevent carriage drift. 
It is noted that the chain 73 is attached to the carriage 28 as nearly as 
feasible to the center of gravity thereof to minimize twisting forces on 
the carriage due to the lifting force. Also, a counterweight 80 may be 
fitted to chain 73 to balance the weight of the carriage 28. 
To provide reference readings to the processing device and to check 
linearity of the detectors, a calibration block 81 is secured to the 
bearing plate 46 of support member 37 as shown in FIG. 3. The block 81 is 
stepped to provide three reference planes for engagement with the distance 
detectors 66(1)-66(3). The center step can be, for example, a zero 
reference plane, the lower step a positive reference plane and the upper 
step a negative reference plane. 
Operation of the measuring fixture is as follows: A flow channel to be 
measured is placed on the support socket 43 and clamped in position by 
clamp arrangement 38 as previously described. Operation of handwheel 77 
moves the carriage 28 along straight edge 27 and the detectors 66(1)-66(3) 
provide signals indicative of the profile of the center and outer tracks 
of their engagement with the adjacent side of the channel. From these 
profile traces, flatness, bow and twist of that side of the channel can be 
determined. The other sides of the channel similarly can be measured by 
release of clamp 38, rotation of the channel by ninety degrees and 
reengagement of the clamp. 
In an embodiment of the measuring fixture the straight edge 27 is about 2 
inches (5.1 cm) thick, 8" (20.3 cm) wide and 14 feet (43 m) long. It is 
formed of carbon steel for machineability, accurately ground and 
electroless nickel plated for corrosion resistance. The holes 33 are about 
5.5 inches (14 cm) diameter spaced about 7.5 (19.1 cm) center-to-center. 
The support beam 14 is an 8 inch (20.3 cm) H beam. This and other 
structural members of the fixture are preferably formed of aluminum to 
minimize the weight of the fixture for ease of portability.