Sony BVU-950 - Page 30

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Wheel
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Edited
Video
2
Framing Servo only with % Servo
Chart-7
So what do we do?
This is where the Phi Square Servo comes in! The name refers to the
fact that U-Matic editors have two phase error loops which are
electronically multiplied, rather than simply added to each other.
Ergo, Phi (phase) Square. Chart-8 shows the addition to the normal
phase error loop to which the Phi square circuit refers. The PG coil
picks up one pulse per revolution of the drum motor (Figure-C). The
digital mono-multi is precisely controlled by the phase error of the
External Video (Input Video) and Reproduced Video (PB Video.) If the
phase of the PB Video is delayed from the Input Video, the digital
counter will count upward how many steps (1 step = 1.1 uSec) are
required to match the phase, and if the PB Video is advanced the
counter will count downward. The result is that the vertical phase
drift is corrected so that the + 1/2 H tolerance is greatly improved,
preventing flagging. We issue specs for + 5.5 uSec tolerance,
compared with the normal 30 uSec of other VTR's.
4-14