Zenith Z-100 PC series Service Manual page 342

The read, write head is a ring with a gap and a coil wound some point on the ring. When current flows through the
coil. the flux induced in the ring fringes at the gap. As the diskette recording surface passes by the gap. the f r i n g e , . ,
flux magnetizes the surface in a longitudinal direction. See figure
4 - 2 . ,
FRINGE
~ ~
CURRENT
OXIDE
RECORDING
SURFACE
FLUX
\Y~-
/
I
..
MYLAR' BASE
DISKETTE MOTION
39211-18
FIGURE 4·2. BASIC READ/WRITE HEAD
The drive WrItes two frequencies:
IF 62.5 k Hz and 2F 125 k Hz. During a write operation. a bit is recorded
when the flux direction in the ring is reversed by rapidly reversing the current in the coil. The fringe flux is reversed
in the gap and hence the porllon of the flux flowing through the oxide recording surface is reversed. If the flux
reversal is instantaneous in comparison to the motion of the diskette.
it
can be seen that the portion of the diskette
surface that just passed under the gap is magnetized one direction while the portion under the gap is magnetzied in
the opposite direction. This flux reversal represents a bit. See figure 4-3.
CURRENT
~CURRENT
RECORDED BIT DISKETTE MOTION
39211·19
FIGURE 4·3. RECORDED BIT
During a read operation. a bit is read when the flux direction in the ring is reversed as a result of a flux reversal on
the diskette surface. The gap first passes over an area that is magnetized in one direction and a constant flux flows
through the ring and coil. The coil registers no output voltage at this point. When a recorded bit passes under the
gap. the flux flowing through the ring and coil will make a 180
0
reversal. This means that the flux reversal in the coii
will cause a voltage output pulse See figure 4-4.
CC)
VOLTAGE PULSE
(FLUX REVERSAL IN GAP)
(\
\
O
/'0)
~
~~
-~----..-----..--------------1:1~
-
r---.:-. -. --.
--------~--~----~----:--!--~------~--~~~~~~.~------------~
RECORDED BIT
DISKETTE MOTION
39211·20
FIGURE 4·4. READING A BIT
These flux reversals produce an FM waveform which transmits data to and from the diskette. See figure 4-5.
IIII~
4-2