Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 157)

Rockwell Automation Publication 1769-UM004B-EN-P - March 2010 157
Glossary
The following terms and abbreviations are used throughout this manual.
For definitions of terms not listed here, refer to the Allen-Bradley 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 ration
(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 Log10 (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.
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).