Rockwell Automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Module - Manual (Page 87)

Publication 1769-UM019A-EN-P - October 2008 87
Glossary
LSB – (Least Significant Bit) The bit that 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 in the card.
For analog inputs, the LSB is defined as the rightmost bit, bit 0, of the
16-bit field. For analog outputs, the three rightmost bits are not
significant, and the LSB is defined as the third bit from the right, bit 2,
of the 16-bit field.
linearity error – An analog input or output is composed of a series
of voltage or current values corresponding to digital codes. For an
ideal analog input or output, the values lie in a straight line spaced by
a voltage or current corresponding to 1 LSB. Any deviation of the
converted input or actual output from this line is the linearity error of
the input or output. The linearity is expressed in percent of full scale
input or output. See the variation from the straight line due to linearity
error (exaggerated) in the example below.
number of significant bits – The power of two that represents the
total number of completely different digital codes an analog signal can
be converted into or generated from.
module scan time – same as module update time
module update time – For inputs, 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 controller. If
output channels are enabled, a constant amount of time must be
added to the input update time to arrive at the total module update
time.
multiplexer – A switching system that allows several signals to share
a common A/D or D/A 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.
normal operating range – Input or output signals are within the
configured range.
Ideal Transfer
Actual Transfer
Function