Rockwell Automation SA3100 AutoMax Distributed Power System - Manual (Page 47)

Glossary A-3
buffer (fiber-optic communications): the protective coating over an optical fiber.
buffer (software): a temporary data storage location.
burst (thyristor or gate control): in IEEE usage, a waveform composed of a pulse train.
bus: a conductor, or pair of conductors, used as a path over which information or
signals are exchanged.
cascaded loops: a multiple series of nested control loops.
CCLK: the constant clock signal on the AutoMax rack backplane that provides a timing
source for modules in the rack. This signal must be driven by only one module in the
rack. The constant clock signal on the AutoMax rack backplane is used to synchronize
hardware interrupts to AutoMax Processors. This signal is required for the UDC
module to be able to execute its tasks.
CEMF: abbreviation for “counter electromotive force,” which is the product of a motor
armature rotating in a magnetic field. This generating action takes place whenever a
motor is rotating. Under stable motoring conditions, this generated voltage (CEMF) is
equal to the voltage supplied to the motor minus IR drop. The polarity of the CEMF is
opposite to that of the power being supplied to the armature.
channel, fiber-optic: consists of two ports and a transmit cable and a receive cable.
The UDC module and PMI provide two channels of fiber-optic communication: COMM
A and COMM B.
cladding (fiber-optic cabling): the material that surrounds the fiber-optic cable’s core.
The cladding has a lower refractive index than the core which optically isolates the
core during data transmissions.
closed loop: refers to a control algorithm in which the actual value of the controlled
variable (e.g., speed) is sensed and a feedback signal proportional to this value is
compared with a reference signal. The difference between these signals (signal error)
causes the actual value to change in the direction that will reduce the difference in
signals to zero.
CML: see loop.
coast to stop: interrupting power and control to the drive, resulting in the drive
slowing to a stop due to windage and load friction.
COMMON (variable): a variable that is defined in the rack configuration and is
therefore accessible to all AutoMax application tasks in the rack. UDC tasks cannot
automatically access common variables. UDC tasks can access only their own dual
port memory.
constant HP range: the range of speeds within which a motor produces constant
horsepower. In this range, torque is inversely proportional to speed.
constant torque range: the range of speeds within which a motor can maintain rated
torque. Horsepower varies directly with speed.
contactor: a two-state (on-off) device for establishing and interrupting an electrical
power circuit. Interruption is obtained by introducing a gap or a very large impedance.