Rotating disc multielement polyphase meter

A single disc multielement polyphase watthour meter having first and second electromagnetic assemblies which apply torque to the disc, the electromagnetic assemblies being mounted with the longitudinal axes thereof located respectively in spaced parallel planes extending parallel to a baseplate of the meter. The meter register includes only decade gearing and the input drive member thereof is coupled to a shaft which mounts the disc over a coupling gear box which includes ratio gearing which adapts a given register for use in registering power consumption in power systems of different current and power ratings.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to electrical meter devices, and more particularly 
to two-element, single disc polyphase watthour meters. 
2. Description of the Prior Art 
Multi-element, single disc polyphase watthour meters have been employed for 
metering polyphase systems for a long time. In recent years, manufacturers 
have directed their efforts toward producing multielement meters which 
provide more accurate readings, are simpler to adjust and which are more 
compact and of lower cost. 
A major problem in single-disc multi-element polyphase meters is the 
interference between the two elements of such meters. As indicated in AIEE 
Transaction Paper, No. 55-483, by W. I. Schmidt, which is entitled "The 
Design of a New 2-Element, Single-Disc Polyphase Meter," made available 
for printing on June 1, 1955, the interference arises from interactions 
between eddy currents in the disc and fluxes from the electromagnetic 
poles of the two electromagnetic elements. The interactions include 
voltage interference, current interference, and voltage-current 
interference. 
Voltage interference and current interference has been substantially 
eliminated by arranging the two electromagnetic elements symmetrically 
with respect to the center of the disc. Generally the elements are mounted 
on a frame secured to a baseplate so as to be positioned in a pair of 
parallel spaced planes extending between front and rear areas of the meter 
and thus perpendicular to the baseplate. The problem of voltage-current 
interference has been more difficult to eliminate. As proposed in the 
Transaction Paper referenced above, one solution to the problem of 
voltage-current interference is obtained through the use of compensating 
windings on the voltage poles. However, the addition of such compensating 
windings increases the cost of the meter. 
The use of a second electromagnetic element in polyphase meters also 
complicates the light load and phase balance adjustments required to 
obtain accurate indications of power usage. The presence of two 
electromagnetic elements operating on a common disc results in 
interactions not experienced in single element meters. Thus, efforts have 
been made to simplify the design of light load and phase balance 
adjusters. 
As indicated above, in known multi-element meters, the two elements are 
mounted perpendicular to the baseplate. While such mounting arrangement 
does not necessarily require an increase in the size of the meter, it does 
generally preclude reduction in the size of the meter which would provide 
a more compact unit. Also, such mounting arrangement necessitates the use 
of a mounting plate and frame which are different from the ones used for 
single element meters, for example. Accordingly, the production costs for 
multi-element polyphase meters, which are relatively low volume units as 
compared to single element meters, are higher than those for single 
element meters, particularly due to the need for two or more castings and 
the use of non-standard parts, that is, parts not used in single element 
meters. 
A further consideration is that the electrical power systems in which 
watthour meters are used may have a number of ratings, and the watthour 
meters, which may be either single or multi-element meters, are required 
to register power usage in systems where the voltage may be 120 VAC or 240 
VAC, and the nominal current may be 2.5, 15 or 30 amps. This requires 
production of five different registers, having different gear trains, to 
permit the dial indicators to provide the correct reading for a given 
rating. 
It would be desireable to have a multi-element polyphase watthour meter in 
which voltage-current interference is minimized without the need for an 
additional compensating winding. It would also be desireable to have a 
polyphase watthour meter having improved accuracy and simplified balance 
adjustments, and which is more compact and of lower cost than known 
multi-element meters. It would further be desireable to have a watthour 
meter which is readily adaptable for use in measuring power usage for 
power systems of different power ratings. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a two-element polyphase 
watthour meter which minimizes voltage-current interference between the 
two elements. 
A further object of the invention is to provide a multi-element polyphase 
watthour meter of improved accuracy and having simplified balance 
adjustments. 
Another object of the invention is to reduce the size and manufacturing 
cost for a multi-element polyphase watthour meter. 
Yet another object of the invention is to provide a watthour meter which is 
readily adaptable for use in measuring power uage in power systems having 
different ratings. 
The present invention has provided a single-disc multielement polyphase 
watthour meter for measuring power consumption of an electrical circuit. 
The meter includes first and second electromagnetic element means each 
including potential and current magnetic structures and winding means 
effective when energized for establishing a shifting magnetic field for 
operating on a common electroconductive disc. The disc is mounted for 
rotation about a vertical axis under the influence of torques generated by 
the electromagnetic element means as a function of power consumption by an 
electrical circuit. The disc is coupled to a register means which provides 
a visual indication of such energy consumption. 
In accordance with the present invention, the meter includes a mounting 
frame which mounts the first and second electromagnetic element means at 
diametrically opposed positions relative to the disc so as to minimize 
voltage interference and current interference between the potential and 
current magnetic structures of the two electromagnetic element means. In 
addition, the first and second electromagnetic element means are mounted 
on the frame with longitudinal axes thereof respectively located in planes 
which extend parallel to a base plate of the meter to which the frame is 
secured. 
It has been found that such parallel mounting of the electromagnetic 
element means minimizes voltage-current interference between the two 
element means without the need for a compensating winding or the like, 
which adds cost to the meter. 
In order to control the influence of the electromagnetic element means on 
the disc, the meter includes balance adjust means and light load adjust 
means. The balance adjust means, which is associated with the potential 
magnetic structure of the first electromagnetic element means permits 
balancing of the torques provided by the two electromagnetic element means 
to provide substantially identical torques for identical operating 
conditions for the two element means. Only one balance adjust means is 
required. 
A counter compensation means, embodied as a shorted coil on the current 
magnetic structures of the two element means, provides compensation for 
phase angle error resulting from overcompensation by the phasing band on 
the potential coil, as well as for temperature affects. 
The light load adjust means, which is associated with the potential 
magnetic structure of the second electromagnetic element means, is 
provided to control the response of the meter to light load conditions of 
the electrical circuit. 
In accordance with a feature of the invention, interference between the two 
electromagnetic element means is further reduced through the use of a 
bridging strip member which extends between the potential magnetic 
structures of the two electromagnetic element means to reduce the 
interaction of stray fields in remote regions of the disc. 
The mounting of the two electromagnetic element means to lie in planes 
extending parallel to the base plate permits the rear electromagnetic 
element means to be located in a cavity formed by the rear surface of the 
frame and an inner surface of the base plate, so that in effect, no 
additional room is needed in the forward portion of the meter for mounting 
the additional element required for multielement meters. This permits a 
reduction in size in order of 25 to 33% for the meter, providing a 
smaller, more attractive meter. Also, the mounting frame is a unitary 
structure having the necessary mounting extensions to permit mounting of 
the parts of the multielement meter in operative relationships. Thus, only 
one casting is required as opposed to the need for two or more castings 
employed in most known multielement polyphase meters. 
Moreover, multielement meters at present are low production items when 
compared with single element meters, for example. The multielement meter 
of the present invention uses many parts which are used in single element 
meters, resulting in substantial cost savings. For example, the rear 
potential element, the light load adjuster, the full load adjuster, and 
the disc and associated upper and lower bearings are the same as those 
used in a single element meter. Also, the current magnetic structures are 
similar, and the base plate is conventional with the addition of an extra 
terminal for the potential windings. All other parts are simple variations 
of those used in existing single phase components. 
In accordance with a further feature of the invention, the register means 
of the meter includes only decade gearing, and an input drive member of 
the decade gearing is coupled to the shaft which mounts the disc, by way 
of a coupling gear assembly means which includes ratio gearing which 
adapts the register for use in electrical circuits of different voltage 
and current ratings. Generally, meters may be employed in circuits having 
voltage ratings of either 120 VAC or 240 VAC, and nominal current ratings 
of 2.5 Amps, 15 Amps or 30 Amps, requiring a manufacturer to stock five 
different registers in order to provide a meter capable of registering 
power consumption on any one of the circuit installations. By way of 
example, the coupling gear assembly means may be provided in five 
different reduction ratings, permitting the use of a given register in a 
number of different applications.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings, there is illustrated in FIG. 1 a multielement 
polyphase watthour meter 20 provided by the present invention. The 
watthour meter 20 which may be used for measuring the energy of a 
three-wire circuit (not shown) includes a multidial register 22 which 
provides a visual indication of energy consumed by an associated load (not 
shown). The register 22 is mechanically coupled to a suitable 
electroconductive armature 24 which in turn is driven by torque applied to 
the armature 24 by a pair of electromagnetic driving element assemblies 30 
and 32, shown best in FIG. 2. 
As illustrated in FIG. 2, the meter 20 is in the form of a detachable meter 
adapted for detachable engagement with a suitable socket receptacle (not 
shown) in a manner known in the art. The meter 20 includes a cover 26 
preferably formed of a transparent material, such as glass, which is 
positioned to surround the operating parts of the meter 20. The cover 26 
is secured to the base plate 28 in a suitable manner, such as by means of 
a rim structure 29. 
As illustrated in FIGS. 2 and 5, each of the electromagnetic driving 
assemblies 30 and 32 is arranged to influence the electroconductive 
armature 24, illustrated in the form of a disc. The disc 24 may be 
constructed of any suitable electroconductive material, such as aluminum, 
and is mounted for rotation relative to the elements 30 and 32 about an 
axis by means of a shaft 36. The shaft 36 includes a worm gear portion 38 
(FIG. 11) positioned to engage a suitable gear 40 forming part of a 
coupling gear box 42 which couples the shaft 36 to the register 22 in a 
manner to be described in more detail hereinafter. 
As illustrated in FIGS. 2 and 3, the assembly 30 includes a voltage coil 50 
and a current coil 51. The voltage coil 50 includes a generally E-shaped 
magnetic structure 52 preferably formed of a plurality of identical 
magnetic laminations 54 each having the configuration illustrated in FIG. 
6. The current coil 51 includes a C-shaped magnetic structure 55 
preferably formed of a plurality of identical magnetic laminations 56 
having the configuration illustrated in FIG. 3. The laminations 54 and 56 
are preferably formed of a low-loss magnetic material, such as silicon 
steel. The structure 52 has a center leg 161 and two side legs 162 and 
163, the ends of which define voltage magnetic poles 164-166, shown in 
FIG. 6. The magnetic structure 55 includes a pair of spaced current 
magnetic poles 64 and 66 having respective pole faces 65 and 67. The poles 
65 and 67 are located in a common plane which is spaced from and parallel 
to the plane defined by the poles 164-166 to define an air gap 68. A 
suitable magnetic shunt 69 may be positioned between the current poles 64 
and 66 to provide overload compensation as is understood in the art. 
The assembly 32 is generally similar to assembly 30 and accordingly, in the 
drawings, similar components of the assemblies 30 and 32 are represented 
by the same reference numerals but with a prime notation added for the 
components of assembly 32. 
In order to permit energization of the magnetic structures 50 and 51, the 
assembly 30 further includes a suitable voltage winding 70 which surrounds 
the center leg 161. The voltage winding 70 is preferably formed of a large 
number of turns of small cross-section conductor. The assembly 30 also 
includes a current winding 72 positioned to surround the current poles 64 
and 66 to produce when energized magnetomotive forces for the poles 64 and 
66 acting in opposing directions. The current winding 72 is preferably 
formed of a relatively few turns of a large cross-section conductor as 
compared to the voltage winding 70. 
As shown best in FIG. 2, the ends 72a and 72b of winding 72 are welded to 
support blades 34 and 35, which extend through a pair of slots, 34a and 
35a, in the base plate 28 (FIG. 3A), to facilitate connection to the load 
by way of a socket receptacle (not shown). The current winding 72' of the 
other driving assembly 32 also has ends connected to a pair of support 
blades, 34' and 35', which extend through a further pair of slots, 34a' 
and 35a', in the base plate 28. 
The ends 70a and 70b of the voltage winding 70 extend through holes 95 and 
95' in the frame to the rear portion of the meter 20. One of the ends 70a 
is connected over a test link 99' to one of the support blades, such as 
support blade 34, and the other end 70b, together with one end 70b' of the 
winding 70' shown in FIG. 2, associated with the rear potential element 
50', may be connected to a pair of tapped stud members extending through 
the base plate 28 and which mount a terminal 99 on the rear surface of the 
base plate 28 as shown in FIG. 3A. The other end 70a' of winding 70' may 
be connected to support blade 34' for the current winding 72'. 
In order to mount the operating parts of the meter 20 to the base plate 28 
of the meter 20 in operative positions a suitable mounting frame 80 is 
provided. The frame 80 may be constructed of a non-magnetic, 
electroconductive die casting material, such as aluminum die casting 
alloy. Such material being electroconductive, offers shielding against 
external magnetic fields. 
The single casting has suitable mounting portions to permit mounting of the 
operative parts of the meter 20 in operative relationships, and also 
affords simpler assembly of the parts on the frame 80, resulting in lower 
assembly costs for the meter 20. 
As shown in FIGS. 2 and 3, the frame 80 is of unitary structure 
construction, and is secured to the base plate 28 by way of a pair of 
mounting bolts 81 which thread apertures (not shown) in the base plate 28. 
The frame 80 is spaced apart from the base plate 28 by way of spacers 85 
which are formed integrally on the peripheral edge 87 of the base plate. 
The frame 80 mounts the magnetic assemblies 30 and 32 with the longitudinal 
axes thereof located in respective parallel spaced planes which extend 
parallel to the base plate 28 in front and rear areas of the meter 20. The 
front magnetic assembly 30 is mounted intermediate the register 22 and the 
frame 80. The rear magnetic assembly 32 is mounted in a cavity 91 defined 
by the rear surface 83 of the frame 80 and a concave inner surface 28' of 
the base plate 28. 
The front potential element assembly 50, and the front current element 
assembly 51 are mounted on the front surface 82 of the frame 80, and the 
rear potential element assembly 50' and the rear current element assembly 
51' are mounted on the rear surface 83 of the frame 80. The front 
potential element assembly 50 is mounted above the disc 24 with its poles 
164-166 disposed adjacent the upper surface of the disc 24. The frame 80 
has a pair of leg portions, such as leg portion 84 shown in FIG. 5, which 
extend perpendicular to the front surface 82 of the frame 80 and have 
tapped holes, such as hole 78, to receive mounting screw 79, which secures 
the potential assembly 50 to the mounting legs 84 in a spaced relationship 
with the front surface 82 of the frame 80. 
The current element assembly 51 is mounted below the disc 24 with its pole 
faces 65 and 67 disposed adjacent to the lower surface of the disc 24. The 
pole faces 65 and 67 are spaced apart from the poles 164-166 of the 
voltage element 50 defining an air gap 68 in which the disc is located. 
The frame 80 has a further pair of mounting legs 86 (FIG. 4) which extend 
perpendicular to the front surface 82 of the frame 80 a parallel spaced 
relation and to which is secured the current element assembly 51 by way of 
screws 87, which thread tapped holes 88 in the legs 86. The frame 80 has 
cutout portions, such as cutout portion 96 shown in FIG. 4, which permit 
the current leads, such as leads 72a and 72b to be extended to the contact 
blades 34 and provide support for the leads. 
Similarly, the rear potential element assembly 50' is mounted to the rear 
surface 83 of the frame 80 by way of raised portion 90 thereof (FIG. 2) 
and is secured to the raised portion 90 by way of mounting screws, such as 
screw 91 which threads a tapped hole 92 is the mounting portion 90 as 
shown in FIG. 5. 
The rear current element assembly 51' is secured to the frame 80 by way of 
extension portions 93 shown in FIG. 4 and is secured to the extension 
portion 93 by way of screws, such as screw 94, which threads a tapped 
aperture 95 in the extension portion 93 as shown in FIG. 5. 
As shown in FIG. 2, the magnetic element 30, including the front potential 
element 50 and the front current element 51, are mounted on the frame 80 
to lie in a plane extending parallel to the frame 80, and thus parallel to 
the base plate 28. The magnetic assembly 32, including the rear potential 
element 50' and the rear current element 51', are mounted to lie in a 
plane which extends parallel to the frame 80 and to the base plate 28. 
It has been found that when the magnetic elements 30 and 32 are mounted to 
extend parallel to the frame and the base plate 28, as in accordance with 
the present invention, the voltage-current interference, generally 
encountered in multielement polyphase watthour meters, is minimized. 
The frame 80 also mounts the register 22 and the shaft 36 mounts the disc 
for rotational movement past the electromagnetic elements 30 and 32. 
Referring to FIG. 5, in order to mount the shaft 36 and the disc 24 for 
rotation relative to the magnetic structures 30 and 32, the frame 80 is 
provided with a pair of projections 100 and 101 which extend from the 
front surface 82 of the frame 80. Suitable upper and lower bearing 
assemblies 102 and 103 are supported respectively, by the projections 100 
and 101 to mount the shaft 36 for rotation about a vertical axis extending 
midway between the two magnetic elements 30 and 32. The disc 24 is secured 
to the shaft 36 in a suitable manner, and is positioned to extend through 
the gaps 68 and 68' provided by the magnetic structures 30 and 32. As 
shown in FIG. 3, the frame 80 has a slot 104 which permits the disc 24 to 
extend through the frame 80. The gaps 68 and 68' are aligned to lie in a 
plane extending transverse to the planes in which the assemblies 30 and 32 
are mounted. 
In accordance with the present invention, the register 22 includes only 
decade gearing, and the coupling gear box assembly 42, which drives the 
register 22, includes ratio gearing related to the current and voltage 
ratings for the circuit to enable the register 22 to be driven to provide 
an indication of power consumption by the circuit. The register 22 and the 
coupling gear assembly 42, which couples the shaft 36 to the register 22 
are also mounted on the frame 80. Referring to FIG. 11, the coupling gear 
assembly 42 includes a reduction gear train 110 the individual gears and 
pinions 110' of which are shaft mounted between front and rear plates 111 
and 112, respectively, and staked at each end. The coupling gear assembly 
42 is mounted to permit a take-off gear 40 to engage the worm gear portion 
38 of the disc shaft 36. Referring to FIG. 3, the coupling gear assembly 
42 is removably secured to the front surface 82 of the frame 80 by way of 
a mounting ear 114, formed integrally with the rear plate 112, and which 
has an aperture 115 through which extends a screw 116 which is received in 
threaded engagement in a tapped hole in the front surface 82 of the frame 
80. 
Referring again to FIG. 11, the output of the coupling gear assembly 42 is 
taken from the output gear 118 by way of a shaft 119, which extends 
through an aperture 120 in the front plate 111, and is coupled to an input 
shaft 124 of the register drive train 125 by way of a coupling link, 
including a spider member 121 carried by the end of the shaft 119 and a 
drive dog 123 carried by the input shaft 124 of the register drive train 
125. A generally U-shaped support member 127 (FIG 2), formed integrally 
with the front plate 111 provides support for the shaft 119 adjacent the 
spider member 121. 
Referring to FIG. 1, the register 22 includes a dial plate 130 over which a 
plurality of digit indicators 131 pass in response to actuation thereof by 
the decade gearing 125. The gear train 125 is actuated in turn from the 
shaft 36 by the intermediate coupling gear assembly 42. The register 22 is 
detachably secured to the frame 80 by way of screws 132 which are received 
in threaded apertures formed in the pillars, such as pillar 133 (FIG. 2) 
which are formed integrally with the front surface 82 of the frame 80. A 
cylindrical spacer 134, interposed between the front plate 135 of the 
register 22 and the tapped surface 136 of the pillar 133, maintains the 
register 22 in the forward portion of the meter 20. 
The coupling gear box 42 may be provided with five different reduction 
ratios to permit application of a given register 22 in circuits which have 
voltage ratings of either 120 VAC or 240 VAC, and current ratings of 
either 2 Amps, 15 Amps or 30 Amps, for example. By way of example, the 
coupling gear box 42 for use in a 120 VAC application may have either one 
of the following reduction gear ratios: 166 2/3; 27 7/9; or 13 8/9 for 
current ratings of 2.5, 15, or 30 amps, respectively. For 240 VAC 
applications, units having the following reduction ratios may be provided: 
83 1/3; 13 8/9; or 6 17/18 for 2.5, 15, or 30 Amp ratings, respectively. 
It is pointed out that while the meter register 22 and associated coupling 
gear assembly 42 are described with reference to an application in a 
polyphase watthour meter, such arrangement may also be used in a single 
element watthour meter or other types of apparatus which employ a 
multidigit register. 
Thus, the ratio gearing is in effect part of the meter, and the register 22 
includes only decade gearing as required to drive the digit indicators 
131. The register 22 is detachably secured to the frame 80, permitting 
substitution of registers having different numbers of dials in a given 
meter. As indicated above, no ratio gearing is used in the register 22, 
and different types of registers -- cyclometers, two rate, demand -- can 
be stocked by a manufacturer in only one ratio-free embodiment for use in 
many different meters, regardless of voltage and current ratings for the 
current with which the meter is used. 
For the purpose of damping rotation of the disc 24 a magnetic damping 
assembly is positioned to influence the disc 24. As illustrated in FIG. 3, 
the damping assembly 140 includes a pair of permanent magnets (not shown) 
enclosed within a generally rectangular shell 142, shown best in FIG. 4, 
which is formed integrally with the front surface 82 of the frame 80 and 
is centered about the slot 104 in the frame 80 through which passes the 
disc 24. The magnets are disposed in a parallel spaced configuration with 
magnetically opposed poles having pole faces 145 and 146 defining gap 147 
in which extends the peripheral edge of the disc 24. 
The magnets may be constructed of any suitable magnetic material, 
preferably a high coercive material, such as high cobalt permanent magnet 
steel. The frame is die-cast around the magnet. The magnet is effectively 
shielded against external magnetic fields by means of the frame 80. 
Magnetic flux of the magnet crosses the gap 147 from pole face 145 to pole 
face 146. A portion of the disc 24 traverses the gap 147 to intercept flux 
from the magnet. For the purpose of adjusting the amount of damping of the 
disc 24, there is provided a damping adjust assembly in the form of an 
adjustable screw 148 and a generally U-shaped mounting bracket 150, both 
of a magnetic permeable material. The bracket 150 is secured to the shell 
142 by way of a screw 152 and has an offset leg portion 153 (FIG. 4) in 
which is received the adjustment screw 148 in threaded engagement. 
The damping adjustment assembly provides a low reluctance path for flux of 
the magnet. The screw 148 is adjustable to increase or decrease the flux 
in the gap 147, and thus the amount of flux passing through the disc 24. A 
retainer spring 151 is provided to hold the screw 148 in any position to 
which it may be adjusted. 
The damping screw 148 is actuable from the front of the meter 20, the 
slotted head of which is accessible through a cutout 154 in a front plate 
135' of the meter register 22 as shown in FIG. 1. 
In order to cause the magnetic elements 30 and 32 to apply substantially 
equal torques to the disc 24 for identical conditions of energization of 
the elements 30 and 32, suitable balance adjusting apparatus 160, shown in 
FIGS. 3, 6, and 9, is provided for adjusting the torque applied by element 
30. As illustrated in FIG. 3, the balance adjust apparatus 160, which is 
associated with the front potential magnetic structure 50, is operable to 
vary the basic torque of the front potential element 50 to permit the 
torques to be equalized at a common load point, typically 100% rated load. 
Referring to the simplified representation of the front potential magnetic 
structure 50, shown in FIG. 6, the magnetic structure 52 is comprised of a 
plurality of E-shaped laminations 54, having a center leg 161 and two 
outer legs 162 and 163. The poles 164, 165 and 166 of the legs of the 
E-shaped core 52 adjacent the disc 24 are spaced apart to provide leakage 
gaps 167 therebetween. It will be understood that the flux which is 
effective in applying torque to the disc 24 is that portion of the flux 
which flows from the outer legs 162 and 163 to the inner leg 161 and 
through the disc 24. By adjusting the amount of flux flowing between these 
legs, it is possible to adjust the torque that is applied for driving the 
disc 24. Most of the flux goes through the gap 167, and only a small 
portion, say 15 to 30% goes through the disc 24. 
The conventional lag loop 168 is provided around the middle leg 161 in 
order to provide the desired flux relationships as will be readily 
understood. 
In order to adjust the flux that threads the disc 24 for varying the torque 
of the element, a magnetic shunt member 170 in the form of a strip of high 
permeability magnetic material is bent in the form shown in FIG. 9, and 
secured to the core 50 by rivets 171 that extend through transverse 
apertures 172 therein. The magnetic shunt member 170 is non-adjustably 
mounted to the core 52. A suitable frame member 172' is secured to the 
core 52 on the side of the core 55 opposite the magnetic shunt member 170 
by way of the rivets 171. 
Intermediate the ends of the magnetic shunt member 170, a threaded aperture 
176 is provided for threadably mounting an adjustment screw 178 that is 
formed of a magnetic material having relatively high permeability. One end 
of the screw 178 is provided with a cylindrical end portion 179 that is 
arranged to move longitudinally in a transverse aperture 180 that extends 
through the middle leg 161 of the core 52. At its other end, the screw 178 
is provided with an adjust wheel 182. A retainer spring 184 is disposed 
between the magnetic shunt member 170 and the adjust wheel 182 in order to 
hold the screw 178 in any position to which it may be adjusted. 
If it is desired to increase the torque that assembly 30 applies to the 
disc 24, the screw 178 may be turned in such direction as to withdraw the 
cylindrical end portion 179 thereof from the aperture 180. The adjustment 
causes less flux to be shunted around the disc 24 and more flux to thread 
the disc 24, thereby increasing the torque applied to the disc 24. The 
torque is decreased by turning the screw 178 in the opposite direction, 
causing less flux to thread the disc 24. The gap 167 can be varied to 
change the torque by approximately 15%. 
When adjusting the phase balance, one tends to over compensate, and as a 
result, there may be a phase angle error in the other direction, that is 
the line voltage is now more than 90.degree. from the output flux. 
Accordingly, current element 51 is provided with a counter compensation 
winding 188 for current element 51, shown in FIG. 3. The winding 188 
comprises two or three turns of copperwire which are wound on the current 
magnetic core 55, and have ends of nickel wire twisted together and 
soldered, forming a shorting loop. The meter 20 is calibrated to work at 
low power factor, and the nickel wire, having a high change in resistance 
with temperature increase provides a convenient way of obtaining Class II 
temperature compensation. 
Referring to FIGS. 3 and 10, for the purpose of providing compensation for 
current damping of the disc 24 at high loads, each of the current elements 
51 and 51' include an overload bridge assembly, such as overload bridge 
assembly 69 for current core 51. The overload bridge assembly 69 includes 
a generally T-shaped bridge member 190 of iron, having a leg portion 191 
which extends through the gap 192 between the current poles 65 and 67, and 
a spacer member 196 of brass, for example, which encircles the part of the 
portion 191 which lies between the poles 65 and 67. 
When the bridge member 190 is unsaturated, flux is shunted away from the 
disc 24. However, the bridge member 190 becomes saturated at higher loads, 
permitting more flux to pass through the disc 24, increasing the torque on 
the disc 24 at higher loads. 
A suitable light load adjuster 200 is provided to control the response of 
the meter 20 to light load conditions of the circuit (not shown). The 
adjuster 200 is associated with the rear potential magnetic structure 51'. 
As shown in FIGS. 7 and 8, the light load adjuster 200 includes an 
electroconductive member 202 which is positioned beneath the voltage poles 
of the magnetic structure 52' in the path of the voltage flux to intercept 
a portion of the voltage flux traversing the gaps between the poles of the 
potential magnetic structure 52'. The structure 52' comprises a plurality 
of E-shaped laminations 54' which are similar to those of the front 
potential core 52 (FIG. 6). The electroconductive member 202 is shown in 
the form of a closed loop effective to lag a portion of the voltage flux 
to develop a torque which is applied to the disc 24. For the purpose of 
providing a variable torque, the member 202 is mounted for adjustment 
relative to the voltage poles, including voltage pole 164' for the center 
leg, and voltage poles 165' and 166' for the outer legs of the E-shaped 
core 52', to intercept a portion of the flux. 
To this end, a suitable actuating mechanism 204 is provided which is 
actuable to effect movement of the member 202 relative to the voltage 
poles along an axis extending parallel to the plane of the magnetic 
structure 52'. As shown best in FIG. 7, the member 202 is carried by a 
U-shaped member 210 having vertically extending end portions 211 and 212. 
A mounting bracket 214 of magnetic material is provided for mounting the 
member 210 by way of an adjustment screw 216 which extends through 
apertures 217 and 219 in respective end portions 218 and 220 of the 
mounting bracket 214, and also through apertures 221 and 222 in the member 
210, aperture 221 being threaded to receive a threaded shank portion 224 
of the screw 216, permitting controlled movement of the member 210 and 
thus of the electroconductive member 202 carried thereby relative to the 
voltage poles 164', 165' and 166'. The mounting bracket 214 is secured to 
the core 52' by way of rivets 226 which extend through transverse 
apertures 227 therein. A suitable frame member 228 is also secured to the 
core on the side opposite the actuating mechanism 204 by way of the rivets 
226. 
A retainer spring 229 is positioned around the shank of the screw 216 
between the end portion 211 of the member 210 and end portion 220 of the 
bracket 214 to maintain the screw 216 in any position to which it may be 
adjusted. 
The customary lag loop 230 is provided around the middle leg of the core 
52' in order to provide the desired flux relationships as is known in the 
art. 
The light load adjuster 200 is adjustable from the front area of the meter 
20 by way of an adjust wheel 231 shown in FIG. 1, which is secured to the 
end of the adjustment screw 216. Movement of the wheel 231 effects 
movement of the electroconductive member 202 relative to the voltage 
poles. The member 202 is positioned so that the compensation torque 
produced by the member 202 tends to rotate the disc 24 in the direction in 
which the disc 24 normally rotates. Since a certain portion of the voltage 
flux is continuously linked by the member 202, the compensation torque 
includes a constant portion which supplies compensation for light load 
error. 
For the purpose of reducing stray fields in the remote regions of the disc 
24, there is provided a bridging strip 240, shown in FIGS. 5 and 12, which 
is positioned with ends 241 and 242 engaging the transverse apertures 
formed in the magnetic structures 52 and 52' of the front and rear 
potential elements 50 and 50'. The strip 240 is generally rectangular in 
shape and has tapered ends 241 and 242 to permit the ends to be inserted 
into the apertures, such as aperture 180 (FIG. 9) for the magnetic core 
structures 52 and 52'. The portion 244 of the strip 240, which is 
intermediate ends 241 and 242, is bowed upwardly and is cut out to fit 
around the shaft 36 which carries the disc 24. 
The bridging member 240 is formed preferably of high permeability material 
in order to provide the desired neutralizing effect. Its width throughout 
its entire length is sufficient to prevent components of the stray 
magnetic field of either magnetic element 50 and 50' from reacting with 
components of eddy currents from the other magnetic structure and 
producing an undesireable torque in the disc 24.