9
Repairs (cont.)
4.
Screw the adjustable plunger into the
backplate of the new electrical assembly.
Place the coil over the plunger and slide the
assembly, with the power cord at the bottom,
into the feeder body (see Figure 7).
5.
Replace the four bolts in the backplate, tune
the feeder as described in “Tuning by Plunger
Adjustment” and tighten down the locking
hex nut.
FIGURE 7
THE Hl-VI MAGNETIC DRIVE
CIRCUIT
Old-style electromagnetic equipment has an
inefficient attract-release type operation, where
a mass mounted on springs is attracted by a DC
electromagnet and returned to its original position
solely by the springs. The new Hi-Vi method
incorporates a lifetime permanent ceramic
magnet and is operated directly from an
alternating current line.
In the Hi-Vi method, the spring-mounted mass is
alternately both attracted and repelled by an AC
electromagnet assisted by the springs.
N
S
N
N
S
AC
POWER
SUPPLY
POTENTIOMETER
ELECTRO-MAGNET
ARMATURE CONNECTED
TO SPRINGS AND
MOVING MASS
PERMANENT
MAGNET
FIGURE 8
Intermeshing a fixed polarity permanent magnet
with an alternating polarity AC electromagnet
eliminates the rectifier since you would have an
alternating attracting and repelling force as the
polarity of the electromagnet alternated.
It will be noted that the pole pieces of the permanent
magnet are intermeshed in the air gaps of an
electromagnet. The polarity of the permanent
magnet is fixed; the polarity of the electromagnet
alternates at the line frequency. We have shown
the polarity of the electromagnet as it would exist
on one side of the sine wave. Note that both poles
of the permanent magnet are being attracted
toward the unlike electromagnet poles. They are
also being repelled in the same direction by the
like electromagnet poles. This results in four forces
accumulating to drive the armature in the same
direction. It also results in closing the magnetic
circuit through the electromagnet providing a
magnetizing effect on the permanent magnet on
each side of the sine wave. The demagnetizing
force is very minor for the attracting force and the
magnetic lines of flux would much prefer to be
attracted than repelled. This always tends to place
the permanent magnet in a magnetizing circuit
regardless of where the AC current is on the sine
wave. As the polarity of the electromagnet changes,
all of the forces are reversed and the permanent
magnet armature is driven in the opposite direction.