Rockwell Automation 1790P-4R0 CompactBlock LDX I/O RTD/Resistance Input Module - Manual (Page 67)

1 Publication 1790-UM002A-EN-P
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 Converter– Refers to the analog to digital converter inherent to the
module. The converter produces a digital value whose magnitude is
proportional to the magnitude of an analog input signal.
attenuation – The reduction in the magnitude of a signal as it passes
through a system.
channel – Refers to input interfaces available on the module’s terminal
block. Each channel is configured for connection to a thermocouple or
millivolt 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.
common mode rejection – For analog inputs, the maximum level to
which a common mode input voltage appears in the numerical value read
by the processor, expressed in dB.
common mode rejection ratio (CMMR) – 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 – The voltage difference between the negative
terminal and analog common during normal differential operation.
common mode voltage range – The largest voltage difference allowed
between either the positive or negative terminal and analog common
during normal differential operation.
cut-off frequency – The frequency at which the input signal is
attenuated 3 dB by a digital filter. Frequency components of the input
signal that are below the cut-off frequency are passed with under 3 dB of
attenuation for low-pass filters.
data word – A 16-bit integer that represents the value of the input
channel. The channel data word is valid only when the channel is
enabled and there are no channel errors. When the channel is disabled
the channel data word is cleared (0).
dB – (decibel) A logarithmic measure of the ratio of two signal levels.
digital filter – A low-pass filter incorporated into the A/D converter. The
digital filter provides very steep roll-off above it’s cut-off frequency, which
provides high frequency noise rejection.