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Glossary
NI 951x User Manual
G-4
ni.com
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.