Rockwell Automation 1746-NI8 SLC 500 Analog Input Modules User Manual - Manual (Page 84)

Publication 1746Ć6.8 - April 1997
Glossary
The following terms and abbreviations are used throughout this
manual. For definitions of terms not listed here refer to
Allen-Bradley’s Industrial Automation Glossary, Publication AG-7.1.
A/D - Refers to the analog to digital converter inherent to the
module. The converter produces a digital value whose magnitude is
proportional to the instantaneous magnitude of an analog input
signal.
analog input module - An I/O module that contains circuits that
convert analog dc input signals to digital values that can be
manipulated by the processor.
attenuation - The reduction in the magnitude of a signal as it passes
through a system.
backplane - A printed circuit board, at the back of the chassis, that
provides electrical interconnection between the modules inserted into
the chassis.
channel - Refers to one of eight, small-signal analog input interfaces
available on the module’s terminal block. Each channel is
configured for connection to a voltage or current source input device,
and has its own data and diagnostic status words.
channel update time - The time required for the module to sample
and convert the input signals of one enabled input channel and
update the channel data word.
chassis - A hardware assembly that houses devices such as I/O
modules, adapter modules, processor modules, and power supplies.
common mode rejection ratio - The ratio of a device’s differential
voltage gain to common mode voltage gain. Expressed in dB,
CMRR is a comparative measure of a device’s ability to reject
interference caused by a voltage common to its input terminals
relative to ground. CMRR=20 Log
10
(V1/V2)
common mode voltage - A voltage that appears in common at both
input terminals of a differential analog input with respect to ground.
configuration word - Contains the channel configuration
information needed by the module to configure and operate each
channel. Information is written to the configuration word through
the logic supplied in your ladder program.