Glossary
AC Alternating current.
AC Contactor An alternating current (AC) contactor is designed for the specific purpose of estab-
lishing or interrupting an AC power circuit.
Ambient Temperature Ambient temperature is the temperature of air, water, or a surrounding medium
where equipment is operated or stored.
American Wire Gauge A standard system used for designing the size of electrical conductors. Gauge
(AWG) numbers have an inverse relationship to size; larger numbers have a smaller cross
sectional area. However, a single-strand conductor has a larger cross-sectional
area than a multi-strand conductor of the same gauge so that they have the same
current-carrying specification.
Block Transfer Block Transfer is the method used by a PLC to transfer data that does not require
continuous updates. To perform this function, the module provides a status word to
the PLC during normal discrete transfer scan. This status word occupies the first
module group in the PLC I/O image table for the designated rack. The status word
is then used by the PLC program to control the BTW and BTR functions of the
PLC.
BTR A PLC Block Transfer Read instruction.
BTW A PLC Block Transfer Write instruction.
Buffer 1. In software terms, a register or group of registers used for temporary storage of
data to compensate for transmission rate differences between the transmitter
and receiving device.
2. In hardware terms, an isolating circuit used to avoid the reaction of one circuit
with another.
Contactor, Reversing A method of reversing motor rotation by the use of two separate contactors, one of
which produces rotation in one direction and the other produces rotation in the op-
posite direction. The contactors are electrically (and mechanically) interlocked so
that both cannot be energized at the same time.
COP This instruction copies data from one location into another. It uses no status bits. If
you need an enable bit, program a parallel output using a storage address.
Cursor The intensified or blinking element in a video display. A means for indication
where data entry or editing occurs.
Cycle 1. A sequence of operations that is repeated regularly.
2. The time it takes for one sequence of operations to occur.
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