IBM 727, Руководство по инструкции

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13.0 SOURCES OF TROUBLE
13.1 SIGNAL DROP OUT
The nomenclature of this term indicates that the voltage amplitude of the signal
was decreased to such a value that it could not be correctly interpreted by the detect­
ing equipment as a one. In general, there are two main causes for this phenomenon.
1. An irregularity on the tape surface may physically lift the tape away from the
reading head at the point where the one is being recorded on the tape. This event
markedly reduces the resulting voltage amplitude obtained when reading. Surface
imperfections can be caused by magnetic oxide clumps, or acetate particles.
2. The lack of magnetic coating caused by wear at the point where a pulse is
supposed to be recorded is another source of signal drop out.
Dirt is one of the major causes of e rro rs in a tape system, whether on the tape
itself or on any of the surfaces which the tape travels over. The slightest lifting of
the tape from the reading head, when reading a one, has a marked effect on the signal
output wave form and amplitude resulting in a signal drop out.
13.2 NOISE PULSES
The difference between signal drop outs and noise is that drop outs are usually
caused by the magnitude of the distance between tape and head or the magnitude of
the discontinuity, while noise is generally a function of the rate of change of the m ove­
ment between tape and head or the rate of change of the discontinuity. Similarly,
noise e rro rs arise from discontinuties in the magnetic coating on the tape surface.
Surface irregularities also contribute to noise.
Other sources of noise or signal drop outs are metal chips that may change the
reluctance of the magnetic path of the flux. Oxide clumps push the tape away from
the head and also change the magnetic reluctance of the flux path.
To eliminate any erro rs originating from the above causes, inspect the tape drive
and associated areas once per shift for any accumulations of dirt, oxide clumps, or
foreign material. Set up and follow a periodic maintenance schedule. The storage of
reels of tape in a hard plastic container has proven to be a great benefit in the control
of dirt affecting the tape.
13.3 SKEW
In a computer system where large amounts of information are stored on tape, it
is desirable to maintain such flexibility that a tape written on any tape unit can beread
on any other tape unit. To attain this interchangeability, it is necessary that tape should
be guided and aligned as perfectly as possible over every read-w rite head. This general
consideration might be termed tape registration. Imperfect tape registration combined
with imperfections of the head geometry (head registration) and variations of the e le c­
trical characteristics of each track give rise to the related problem s of skew and tracking.
Skew is the name given to the phenomenon in which bits composing a character,
though written at the same instant of tim e, are not read at the same instant of time.
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