IBM 727, Руководство по инструкции

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4.12 FILE PROTECTION
A device is provided to prevent writing on a reel of tape if so desired. This
device consists of a groove cut in the rear side of the file reel and an associated
ring which fits into the groove. If the ring is not placed in the groove, writing is
suppressed but reading is allowed. If the ring is placed in the groove, both reading
and writing may occur.
To sense the presence or absence of the ring, a pin protrudes from the upper
main plate. The pin is connected to the armature of a duo relay mounted directly
behind the upper main plate. If a ring is in the groove of the file reel, the pin is
pushed to the rear, causing the relay armature to be sealed. This action transfers
the relay contacts to energize the relay and also allow writing to occu r. If the groove
in the reel is empty, the pin is not actuated and the relay is not energized; normal
writing is prevented.
4.13 POWER CONSIDERATIONS
All external power is brought into the tape unit through a male Cannon plug lo ­
cated at the lower rear right-hand corner of the tape unit. Power may be jumpered to
other tape units by connecting the female Cannon outlet located beside the male inlet
plug. Drive motor operation requires 30 , 208v, AC power. One phase of the 30
supply is used to operate the 48v DC supply located within the tape unit. The 48 volts
is necessary for relay operation.
The +270v, +140v, -60v, -130v, -270v, and +40v are brought from external’
supplies. The 40v is used only to light a thermal light in the event that the tempera­
ture within the unit becom es excessive.
4.14 MACHINE REEL SENSING ARM
The sensing arm rides on the surface of the tape on the machine reel, and has an
associated contact. When more than a half inch of tape is on the machine reel, the
contact is open; when less than one-half inch of tape is on the machine reel, the con­
tact is closed.
The purpose of this arm and contact is discussed under "High-Speed Rewind" in
section 10. 0.