Rockwell Automation 1769-OF4 Compact Analog Output Module - Manual (Page 68)

68 Publication 1769-UM020A-EN-P - December 2009
Glossary
full scale range – (FSR) The difference between the maximum and
minimum specified analog input values.
hold last state – A configuration selection that instructs the module to
keep the outputs at the last converted value prior to the condition that
caused the control system to enter the Fault or Program mode.
input image – The input from the module to the controller. The input
image contains the module data words and status bits.
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 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 output. The linearity is expressed in percent of full scale 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 – See module update time .
module update time – The time required for the module to receive,
convert, and drive all output data for the enabled output channels.
multiplexer – A switching system that allows several signals to share
a common A/D or D/A converter.
normal operating range – Input or output signals are within the
configured range.
Ideal Transfer
Actual Transfer
Function