Allen-Bradley SLC 500 1746-NR4, User Manual

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Preface
P–4
The following terms and abbreviations are specific to this product. For a
complete listing of Allen–Bradley terminology, refer to the Allen–Bradley
Industrial Automation Glossary, Publication Number AG–7.1.
A/D – Refers to the analog–to–digital converter inherent to the
RTD/Resistance 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.
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 an RTD or potentiometer 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.
common mode rejection ratio – The ratio of a device’s differential voltage
gain to common mode voltage gain, expressed in dB.
CMRR = 20 Log
10 (V1/V2)
common mode voltage – A voltage signal induced in conductors with
respect to ground (0 potential).
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.
cut–off frequency – The frequency at which the input signal is attenuated
3dB by the digital filter. Frequency components of the input signal below the
cut–off frequency are passed with under 3dB of attenuation.
data word – A 16–bit integer that represents the value of the analog 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 noise filter incorporated into the A/D converter.
In addition, the digital filter provides high–rejection notches at frequencies
that are integral multiples of the filter cut–off frequency. The notches are
used for rejecting AC power line noise and higher frequency noise.
excitation current – A user–selectable current (0.5 mA and 2.0 mA) that the
module sends through the RTD or resistive device to produce an analog
signal which the NR4 can process and convert to temperature or to ohms,
respectively.
Terms and Abbreviations
AB Spares