Rockwell Automation 1762-IT4 Thermocouple/mV Input Module - Manual (Page 135)

1 Publication 1762-UM002A-EN-P - July 2002
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.
bus connector – A 16-pin male and female connector that provides
electrical interconnection between the modules.
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.
CJC – Cold junction compensation. CJC is the means by which the
module compensates for the offset voltage error introduced by the
temperature at the junction between a thermocouple lead wire and
the module terminal block (the cold junction).
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.
configuration word – Word containing the channel configuration
information needed by the module to configure and operate each
channel.