Note: Descriptions are shown in the official language in which they were submitted.
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COMPACT MOVING COIL METER
This invention relates to a compact moving coil
meter employing the D'Arsonval principle. The improved
-;; meter mechanism according to this invention has particular
utility in the environment of an edge-wise compact meter.
BACKGROUND OF THE INVENTION
~` Thin flat meters typically on the order of
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~ one-half inch thick in the direction of the axis of the
-~ meter movement are known in the art. Such shallow meters
are frequently referred to as "compact". A typical
mechanism for such meters is disclosed in U.S. Patent
No. 3,621,393, issued November 16, 1971.
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In the mechanism of the above-mentioned patent,
~ cements and epoxies are used to secure the parts of the ~
-~; rotor or moving element together, and cement is also used
to secure the permanent magnet to a first magnetically
permeable plate of the mechanism. A second magnetically
permeable plate parallel to the first plate, is magneti-
cally connected to the first plate by spacers and screws,
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to provide an arcuate gap to accommodate the moving coil
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for movement along the first plate and magnet.
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~hile the construction disclosed in this afore-
mentioned pa~ent provides a meter of good accuracy which
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can be assembled on a mass production basis, the meter is
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somewhat expensive, because of the number of parts which
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I must be separately manufactured and aligned during assembly.
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SUMMARY OF THE INVENTION
The present invention is directed to an eccentric coil meterincluding a base, a rotor assembly mounted on the base for pivotal move-
ment about an axis, a magnetic circuit at one side of the axis, said
rotor assembly comprising a unitary balance cross of electrically con-
ducting material, a coil supported by the balance cross and radially
disposed on the same side of the pivot axis as the magnetic circuit, a
pointer supported by the balance cross and on the opposite side of the
axis from the magnetic circuit, and a terminal supported by the balance
cross and electrically insulated therefrom, said balance cross including
a leg generally parallel with the axis and on the same side of the axis
as the magnetic circuit, and a body portion including a pointer support
portion the opposite side of the axis from the magnetic circuit, means
for securing said coil to the balance cross leg and comprising oppositely
opening notches in said leg, and tabs on said coil assembly and bendable
across said leg to secure said coil assembly to the leg, means for secur-
ing said pointer to the pointer support portion of said balance cross and
comprising locating edges on pointer support portion and tabs on said
pointer engaging said locating edges and bendable across said body portion
to secure the pointer to the balance cross, means securing said terminal
to said balance cross and comprising terminal locating edges on said
balance cross, and tabs projecting in the same direction from said terminal
and bendable across said body portion to secure the terminal to the
balance cross, means between the balance cross and terminal for insulating
the terminal from the balance cross, a second terminal carried by the
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s balance cross, said coil assembly including a winding having one end
, thereof electrically connected to said first mentioned :~
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terminal and the other end thereof electrically connected to ~aid ~econd
- terminal, and means secured to said balance cross ~or pivotally mounting said
rotor assembly on the ba~e.
Numerou~ other ~eature~, objects and advantages of the meter
construction o~ thiq invention will become apparent with reference to the
accompanying drawings.
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~RIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an exploded pictorial view showing a meter mechanism and
¢asing;
Fig. 2 is an exploded pictorial view of the meter mechanism o~ Fig. l;
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Fig. 3 is a bottom plan view of the meter mechanism bridge with the
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magnet shown in dotted lines;
- Fig. 4 is an exploded pictorial view of the rotor of this invention;
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j Fi~. 5 is an enlarged front elevational view in partial section oP
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the meter movement and casing~
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Fig. 6 is a rear elevational view of the meter mechanism with a
: magnet o~ a ~irst thickness; and
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Fig. 7 i3 a view corresponding to Fig. 6 and showing the mechanism
; with a magnet o~ dif~erent thickness.
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~ 20 DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
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Referring to Fig. 1, there is shown a meter which includes a meter
movement 10 having a casing 12 including a cover 14 and a transparsnt lens
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16. A suitable qcale 18 is ~ixed to the front of caqing 12, ~or example, with
a pressure sensitive adhesive ~trip 19. There is a space beSween scale 18 and
len~ 16 to accommodate pointer tip 20. Meter movement 10 is secured in casing
12 with ~crews that mount the meter movement on posts 22 of the casing, and
which have their upper ends elevated with respect to ~he ~loor or bottom wall
24 of the casing.
Offset toward the rear o~ the casing 12 is a recess 26 with a flat
upper surface on which a zero adJu~t arm 28 can slide arcuately. An opening
29 in the zero adjust arm ~eat~ on a shallow post 30 in rece~s 26 to mount the
arm for pivotal movement. A zero ad~ust knob 32 enter~ through opening 34 in
the rear wall of the casing and has its eccentric tip 36 disposed in slot 38
o~ the upright leg of the zero adjust arm. Knob 32 is held in position in the
ca3ing by a downwardly projecting tab 40 at the rear of the cover, the tab
having an opening to expose the end of the knob for adjustment with a screw
drlver. Cover 14 is a slide fit on casing 12 and lens 16 is a snap fit into
the cover and càsing.
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Referring to Fig. 2, meter movement 10 includes a moveable assembly
or rotor 44, and a stationary assembly. The stationary assembly includes a
unitary base or bridge 46 which can be a die cast metal or molded plastic and
is of non-magnetic material. Base 46 has a pair oP mounting arms 48 which
project forwardly from body portion 50 and
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diverge with respect to each other. A pair of magnetic circuit supportlegs 52 project rearwardly from body portion 50 and also diverge with
respect to each other.
The magnetic circuit includes a generally arcuate magnet 54,
a magnet support 56 of magnetically permeable material, and a clamp plate
58, also of magnetically permeable material. Clamp plate 58 and support
56 secure magnet 54 to base 46 when the magnetic circuit is assembled to
the base.
Body 50 of the base 46 has a generally rectangular opening 60
to receive rotor 44. An upper terminal 62 is mounted on the under side of
an upper cross leg 64 of the body, in electrically insulated relation to the
body, and for limited pivotal movement. A lower terminal and zero adjust
member 66 is mounted on the under side of lower cross leg 68, for limited
pivotal movement. Hubs 70 and 72 are internally threaded to receive
jeweled pivot bearings 71 and 73 for pivotally supporting the rotor on
the base.
Projecting arcuately toward each other from the ends of the
magnet support legs 52 are ears 74, each having an arcuate opening 76 to
receive a coil stop 78. The coil stops are preferably formed from an
insulating material such as a plastic or a molded ceramic. These stops 78
` limit the extent of pivotal movement of the rotor assembly.
Formed in the top face of each magnet support leg 52 are spaced
apart support ribs 80, 81 which provide a seat for clamp plate 58. Clamp
`' plate 58 is of uniform thickness throughout its active portion 83 between
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bends 84 and 86 which provide offset ends 88 and 90, the upper and lower
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surfaces of which are essentially flat and parallel. The ends 88 and 90
are offset upwardly with respect to the plane of active portion 83, when
the clamp plate is in the position shown at Fig. 2. Edges 92 and 94 of
~` the respective ends 88 and 90 are essentially flat to engaga and locate
against flat locating surfaces 96 and 98 respectively of the base.
Magnet support plate 56 is generally U-shaped, having a flat
body portion 99 of uniform thickness and upright legs 100 and 102
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terminating at outwardly turned ends la4 and 106. The upper su~faces of
ends 104 and l06 are flat and coplanar to provide s~lbstantial surface
engagement with the flat coplanar surfaces of ends 88 and 90 of clamp
plate 58. Such flatness and substantial surface engàgement between the
ends of the support 56 and clamp plate 58 minimize reluctance of the
magnetic circuit. The inner edge of support plate 56 has locating faces
108, 110, 112 and 114, at each side, which engage the rear of body 50 to
precisely locate the clamp plate with respect to the body of base 46.
~- As shown at Fig. 3, the lower portion of the base includes a continuation
; 10 of the surfaces 96 and 98. Locating faces 108, 110, and 112 of support
plate 56 engage and locate against face 96 at one side of the base and
face 98 at the other side of the base. Faces 112 and 114 engage at the
corner between surfaces 98 and a rear surface 116 of the body portion 50
of the base.
Fig. 3, which is a bottom view of the base without its terminals,
shows the locating surfaces of the base 46 which cooperate with the magnet
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to precisely position the magnet with respect to the base. Such surfaces
include a horizontal surface 120 on one leg, and a coplanar horizontal
surface 122 on the other leg. Projecting perpendicularly from surface
~- 20 120 is a surface 124, and projecting perpendicularly from surface 122 is a
,, surface 126. Ears 74 each have locating surfaces 128 and 130 respectively.
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` Magnet 54 is shown in phantom lines in position between the surfaces 124,
126, 128 and 130. Correspondingly, it is apparent that side faces 132, 134
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i of the magnet (Fig. 2) locate precisely against surfaces 124 and 126
(Fig. 3) respectively, and the arcuate outer surface 136 of the magnet
locates against surfaces 128 and 130 of the base. In addition, the flat
top face 138 of the magnet locates near its ends on surfaces 120 and 122
~` of the base. As a result, the locating surfaces of the base precisely
position the magnet with respect to the base. Magnet 54 is of a
permanent magnet material such as Alnico, has its top face 138 parallel
with its lower surface 140, and is magnetized in a direction perpendicular
to faces 138 and 140. By virtue of the locating surfaces on clamp plate
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58, magnet 54, and magnet support 56J and the locating surfaces on the base,
the magnetic circuit is precisely located on the base by the simple expedient
of positioning these elements on the base and securing the clamp plate to the
magnet support with hollow rivets 142.
Fig. 4 shows rotor 44 of the meter of this invention. A unitary
balance cross 150, formed from sheet metal, has an elongated flat body
portion 151 with a generally centrally formed opening 152 to receive a
pivot 154 which is pressed into the opening to secure the pivot to the
balance cross. A tail 156 is bent at a right angle to the plane of body
151, this tail having a pair of outwardly opening notches 158 and a wire
receiving terminal 160. A coil assembly includes a coil form 162 and a
coil 164 wound on the form. The coil form is of sheet metal and has
securing tabs 166 spaced apart to enter the notches 158 of upright leg
156. Tabs 166 are each tapered, and are a close fit in notches 158 so
the coil assembly is precisely located with respect to the plane of body
151 of the balance cross. Coplanar edges 168 of the coil form, above and
below each tab 166, abut the rear face 170 of leg 156 above and below each
notch 158 so the coil assembly extends perpendicular to leg 156 and is
precisely parallel to the plane of body 151. Such precise positioning is
i 20 obtained by merely moving the tabs 166 through notches 158 until edges 168
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~- abut the leg, and then bending the tabs inwardly to the position shown at
; Fig. 2, to secure the coil to the leg.
Formed in body 151 slightly inwardly of rear leg 156 is a
rectangular opening 172. Side edges 174 of the body between this opening
and a hub portion 176 of the balance cross are essentially straight and
parallel to each other.
A pair of balance weight receiving arms 178 project diametrically
outwardly from hub 176. Formed in the forward portion of balance cross 150,
near hub 176 is a spring connecting arm 180. Arm 180 is preferably
parallel with the axis of pivot assembly 154.
The forward portion of balance cross 150 includes edges 182,
a pair of notches 184 and a second pair of notches 186, open at their
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forward ends to define rectangular lugs 188 between these notches.
Balance cross 150 also has a forwardly extending stem 190 which is bent
to slope upwardly, and which receives a balance weight 192 at its end
Pointer 194 is of sheet metal and includes the down turned
pointer tip 20 at one end, and pairs of pointer securing tabs 196, 198,
and 200 at its other end. The body of the pointer between the ends is
offset so the forward portion 202 of the pointer is in a plane above and
parallel with inner end portion 204. The distance between the pairs of
tabs 196, 198, and 200 is the same as the distance between the edges of
the respective notches 186, lugs 188, and notches 184. Correspondingly, ``
pointer 194 is accurately positioned and secured to the forward portion
of balance cross 150 by simply moving the pointer upwardly as shown at
Fig. 4 until tabs 196 and 200 locate in notches 186 and 184 respectively,
whereupon tabs 196, 198, and 200 are bent over, to the position shown at
Fig. 2, to clamp the pointer to the balance cross.
One end 206 of winding 164 is secured to terminal tab 160 of
upright leg 156. The other end 208 of the winding is connected to a
terminal element 210. Terminal element 210 has an arm 212 to which wire
208 is secured. The terminal element has a hub 214 with an opening through
2Q which pivot assembly 154 extends. At one side of the hub are a pair of
parallel tabs 216 and an end tab 218. At the other side of the hub are
~- parallel tabs 220. Projecting downwardly from the front of the hub is a
return spring connecting tab 222.
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` Positioned between terminal 210 and balance cross 150 is a
sheet material insulator 224 of a configuration conforming with the
configuration of terminal 210. It will be observed from Fig. 4 that
insulator 224 has tabs 226 and 228 at one side of its hub, and tabs 230
at the other side of its hub. The insulator fits against terminal 210 with
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its tabs inside the corresponding tabs of the terminal. Terminal 210 is
~?,` 30 secured to balance cross 150 by first positioning insulator 224 on the
balance cross and by then positioning the terminal on the balance cross
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and bending the respective tabs 216, 218, and 220 across the balance cross
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to secure the terrninal in position. Tab 218 is smaller than the rectangular
opening 172 and insulating tab 228 of the insulator, so tab 2l8 is
electrically insulated from the balance cross. Similarly, tabs 216 and
220 of the terminal are smaller than insulator tabs 226 and 230. When the
several tabs of terminal 210 are bent across the balance cross, the
terminal is secured to but insulated from the balance cross. The inner end
232 of lower return spring 234 is secured to spring arm 222. The terrninal
is so dimens;oned that there is a space between its front edge 236 and rear
edge 238 of pointer 194, to avoid grounding the terminal through the metal
of the pointer. Securing the inner end of spring 240 to spring connecting
arm 18Q completes the assembly of the rotor.
The various parts of the meter mechanism shown at Fig. 2 are
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assembled in the following manner to provide the meter mechanism 10, shown
, at Figs. 1 and 5. Referring to Fig. 2, after the rotor assembly 44 is
`~ assembled, as described above with reference to Fig. 4, the entire rotor
assembly 44 is inserted through opening 60 of base 46, with the coil 164
between magnet support legs 52, and with pivot assembly 154 generally
aligned with the axis of hubs 70 and 72. Next, stops 78 are inserted
i~ into openings 76 in rear legs 74. Clamp plate 58, is then threaded
through opening 242 in the coil assembly. With the parts so positioned,
-~ jeweled pivot bearings 71 and 73 are threaded into the hubs to mount
~- rotor assembly 44 for pivotal movement. It will be seen from Fig. 5,
that with the meter rnovement disposed horizontally in its normal operating
position, pivot assembly 154 is vertical, and the rotor is mounted to
rotate about a vertical axis.
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Fig. 5 also shows in greater detail, a staked or swaged insert
i 246 which mounts terminal 66 for limited pivotal movement, and a staked
or swaged insert 248 which mounts terminal 62 via an intermediary insulating
bushing 250.
Magnet 54 is then seated against the base in the manner previously
described with reference to Fig. 3. Then, magnet support plate 56 is
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placed beneath the magnet, and hollow rivets 142 are inserted through the
openings in clamp plate 58 and magnet support 56. Plates 58 and 56 are
then pushed inwardly toward hub 70 so edges 92 and 94 abut locating
surfaces 96 and 98 of the base, and surfaces 108, 110, 112 and 114 abut
the respective locating surfaces 98 and 116 of the base. A clamping
pressure is then applied between ends 88 and 104 and between ends 90
and lQ6 of the clamp and magnet support plates. While this clamping
pressure is maintained, hollow rivets 142 are upset to rivet the plates
together to secure the plates and magnet 54 to the base. Correspondingly,
by the simple expedient of positioning the magnet against the locating
surfaces of the base, and positioning clamp plate 58 and magnet support
plate 56 against the locating surfaces on the base, it is assured that
these parts of the magnetic circuit are in a predetermined position with
respect to the rotor assembly. Such predetermined positioning, in
successively assembled meters, provides repeatable accuracy with minimal
calibration. By virtue of the flat engaging faces of the ends of clamp
` plate 58 and magnet support plate 56, a closed loop magnetic circuit of
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minimal reluctance between the plates is provided.
As shown at Fig. 5, there is an air gap 252 between clamp plate
58 and magnet 54. Lower leg 254 of the coil assembly extends through
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this gap. As previously mentioned, magnet 54 is magnetized in a direction
~- parallel to the axis of rotation of the rotor, and correspondingly, when
the coil is energized, a magnetic force is created which causes the coil
and rotor to pi~ot about the meter axis.
With the rotor 44 in position and the magnetic circuit
; assembled, the outer ends of return springs 234 and 240 are secured
` respectively to base terminal 62 and base terminal 66. As shown atFig. 5, terminal 62 has a downwardly projecting tab 260 to which the
outer end of spring 240 is secured as by welding. Similarly, terminal
` 30 66 has an upwardly projecting tab 262 to which the outer end of lower
. spring 234 is secured by welding. The limited pivotal movement of
terminals 62 and 66 provides for adjusting the zero point of the rotor.
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Wires 262 and 264 are connected respectively to terminals 62 and 66.
These wires extend to the rear of the casing 12 and are connected to terminal
screws ~not shown), via which external connections are made to the meter.
With reference to Figs. 1, 2, 4 and 5 it will be apparent that
the coil 164 is electrically connected in series between terminal wires
262 and 264, the electrical path including wire 262, terminal 62, return
spring 240, arm 180 of the balance cross, the balance cross body 151,
terminal 160 of the balance cross, wire 206 of the coil, coil 164, wire
208 of the coil, terminal arm 212 of terminal 210, spring 234, terminal
66 and wire 264.
Figs. 6 and 7 show a distinct advantage of meter mechanism 10
including clamp plate 58 with offset ends 88 and 90. Fig. 6 is a rear
view of the embodiment of Figs. 1-5 where clamp plate 58 is secured to
magnet support plate 56 with the ends 88 and 90 of the clamp plate
projecting upwardly with respect to the plane of the active portion or
; body 83 of the clamp plate. In order to locate and hold the magnet 54
`~ in position against any movement, even if the meter movement is dropped
or otherwise abused, the magnet 54 has a thickness such that a clamping
pressure is required to initially bring the ends of the clamp plate and
magnet support plate into engagement. Correspondingly, with reference
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to Fig. 6, the thickness or height of magnet 54 plus the thickness of
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that portion of a magnet support leg 52 between its lower surface 120,
and the top of its ribs 80 is very slightly greater than the distance
between upper surface 272 of magnet support 56 and lower surface 274 of
m~ clamp plate 58. In the meter of Figs. 1-6, the flux density produced in
air gap 252 by magnet 54 is sufficient to provide a meter movement of good
sensitivity, on the order of 50 microamps. Where a far more sensitive
meter is required, the construction of Fig. 7 can be used, this construction
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requiring only a thicker magnet to obtain a more sensitive meter movement.
Referring to Fig. 7, a clamp plate 58 identical to clamp plate 58
of Fig. 6, but inverted, secures magnet support 56 and a magnet 275 in
position on the base. Magnet 275 has a thickness which is greater than
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the tl~ickness of magnet 54 by an amount equal to twice the offset 276 of
ends 88 and 90 of the clamp plate 58 with respect to its body 83. As
shown at Fig. 7, coil 164 is in precisely the same position with respect
to the base 46 as the coil is in the embodiment of Fig. 6. The same support
plate 56 is used in the Fig. 7 embodiment. Since body portion 83 of clamp
plate 58 is flat and parallel, the ribs 80 position this body in the same
plane with respect to the coil and base, as in the Fig. 6 embodiment.
Correspondingly, a more sensitive meter is obtained merely by substituting
the thicker magnet 275 for the magnet 54, and inverting clamp plate 58.
The meter movement of Fig. 7 has a height greater than the meter
of Fig. 6, by an amount equal to the greater thickness of magnet 275.
Casing 12 of Fig. 1 can be used with the thicker or higher meter movement
of Fig. 7 by the simple expedient of providing spacing washers 266 (Fig 1),
between the mounting legs 48 and support posts Z2 of the casing. Such
- washers elevate the meter mechanism slightly with respect to the base and ?
recess 26, so the bottom face of magnet support 56 will clear projection
30 at recess 26 of the base.
~- Correspondingly, by virtue of the unique clamping arrangement
. of the magnetic circuit of the meter of this invention, only one additional
, 20 part, namely a thicker magnet, is required to obtain substantially greater
;~ sensitivity, all other parts remaining essentially the same..~ Of course, where magnets of a tliickness different from magnet
54 or magnet 275 are required in order to construct meter movements of a
desired sensitivity, clamp plate 58 can be flat, and a magnet support 56
of the required depth to clamp the magnet to the legs 52 can be used.
This magnet support can have a depth either greater or shallower than
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the magnet support 56. Alternatively, a clamp plate with ends 88 and
9a offset either more or less than those of the clamp plate 58 can be
, used with the magnet support plate 56 to accommodate magnets of a thick-
ness different from magnets 54 and 275.
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Since the plane of the active portion 83 of clamp plate 58 is
determined by the engagement of plate 58 with the ribs 8~ on legs 52 of
the bridge, and since the coil 164 extends around clamp plate 58 and not
around the magnet and magnet support plate, the same bridge and rotor can
be used to construct meters of different sensitivity by the simple
expedient of substituting a magnet of the required thickness, and using
either the clamp plate and magnet support plate shown at Figs. 6 or 7,
or using the modifieid clamp plate and magnet support plate mentioned
above. Such construction is possible since the rotor and bridge are so
constructed and arranged that there is no obstruction in the region
occupied by the magnet and magnet support plate which prevents the use
of either a thicker magnet or a support of greater height than the one
shown at Figs. 6 and 7.
While preferred embodiments of a meter assembly including the
unique meter mechanism of this invention are shown and described herein,
it will be appreciated that changes can be made without departing from
the scope of the invention as mentioned herein and defined in the appended
clai~s.
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