Rockwell Automation 1769-OF4VI Compact I/O Isolated Analog Modules - Manual (Page 121)

Publication 1769-UM014B-EN-P - May 2010
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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 input modules, 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. For output modules, the
time required for the module to receive the digital code from the controller,
convert it to the analog output signal, and send it to the output channel.
multiplexer – An 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. See page 1-2 for a list of input and output types/ranges.
overall accuracy – The worst-case deviation of the output voltage or current
from the ideal over the full output range is the overall accuracy. For inputs, the
worst-case deviation of the digital representation of the input signal from the
Ideal Transfer
Actual Transfer
Function