National Instruments NI 9512 User Manual - page 67
Glossary
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N
noise
An undesirable electrical signal—Noise comes from external sources
such as the AC power line, motors, generators, transformers,
fluorescent lights, soldering irons, CRT displays, computers, electrical
storms, welders, radio transmitters, and internal sources such as
semiconductors, resistors, and capacitors. Noise corrupts signals you
are trying to send or receive.
O
off
An input or output is off when current is not flowing through the input
or output circuit.
on
An input or output is on when current is flowing through the input or
output circuit.
open-loop
A control system where no external sensors (feedback devices) are
used to achieve control of the system.
P
p-command
A command mode used for certain types of servo motor drives that
accept step and direction (CW/CCW) information to drive a servo
motor.
PID control loop
proportional-integral-derivative control loop—A control method in
which the controller output is proportional to the error, the sum of all
previous errors, and the rate at which the error is changing. The error
is the difference between the observed and the commanded values of
the device that is being controlled.
PIVff control loop
proportional-integral-velocity feed forward control loop—A control
method in which the controller output is proportional to the error, the
sum of all previous errors, and the future trajectory velocity. The error
is the difference between the observed and the commanded values of
the device that is being controlled.
position capture input
Record position based on an external event.
position compare
output
When the encoder reaches a user-specified position, the associated
position compare output performs the user-specified action.