Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 121)

1 Publication 1746-UM007C-EN-P - July 2004
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 NT4
thermocouple input module. The converter produces a digital value
whose magnitude is proportional to the instantaneous magnitude of
an analog input signal.
attenuation - The reduction in the magnitude of a signal as it passes
through a system. The opposite of gain.
channel - Refers to one of four, small-signal analog input interfaces
available on the module’s terminal block. Each channel is configured
for connection to a thermocouple or DC millivolt (mV) input device,
and has its own diagnostic status word.
chassis - A hardware assembly that houses devices such as I/O
modules, adapter modules, processor modules, and power supplies.
CJC (Cold Junction Compensation) - The means by which the module
compensates for the offset voltage error introduced by the
temperature at the junction between the thermocouple lead wire and
the input terminal block (the cold junction).
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 Log10 (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.
cutoff frequency - The frequency at which the input signal is
attenuated 3 dB by the digital filter. Frequency components of the
input signal below the cut-off frequency are passed with under 3dB of
attenuation.
dB (decibel) - A logarithmic measure of the ratio of two signal levels.