Rockwell Automation 1769-IR6 Compact I/O 1769-IR6 RTD/Resistance Input Module - Manual (Page 113)

Rockwell Automation Publication 1769-UM005B-EN-P - March 2012 113
Glossary
linearity error – Any deviation of the converted input or actual output from a
straight line of values representing the ideal analog input. An analog input is
composed of a series of input values corresponding to digital codes. For an
ideal analog input, the values lie in a straight line spaced by inputs
corresponding to 1 LSB. Linearity is expressed in percent full-scale input. See
the variation from the straight line due to linearity error (exaggerated) in the
example below.
LSB – Least significant bit. The LSB represents the smallest value within a
string of bits. For analog modules, 16-bit, two’s complement binary codes are
used in the I/O image. For analog inputs, the LSB is defined as the rightmost
bit of the 16-bit field (bit 0). The weight of the LSB value is defined as the
full-scale range divided by the resolution.
module scan time – same as module update time
module update time – The time required for the module to sample and
convert the input signals of all enabled input channels and make the resulting
data values available to the processor.
multiplexer – A switching system that lets several signals share a common
A/D converter.
normal mode rejection – (differential mode rejection) A logarithmic
measure, in dB, of a device’s ability to reject noise signals between or among
circuit signal conductors. The measurement does not apply to noise signals
between the equipment grounding conductor or signal reference structure and
the signal conductors.
number of significant bits – The power of two that represents the total
number of completely different digital codes to which an analog signal can be
converted or from which it can be generated.
overall accuracy – The worst-case deviation of the digital representation of
the input signal from the ideal over the full input range is the overall accuracy.
Overall accuracy is expressed in percent of full scale.
repeatability – The closeness of agreement among repeated measurements of
the same variable under the same conditions.
Ideal Transfer
Actual Transfer
Function