SNAP Analog Input Modules
™
use PAC Manager software to calculate and set offset and
gain.
and below zero. An example of this is the SNAP-AIV module,
which has a range of -10 to +10 VDC.
Some modules are considered unipolar, which means the
range starts or ends at zero. For example, the SNAP-AIVRMS
module has a range of 0 to 250 VAC because AC current
cannot be negative.
Isolation
All SNAP analog input modules are isolated from all other
modules and from the SNAP I/O processor. The modules in
this data sheet do not have channel-to-channel isolation,
however. (If you need isolated analog modules, see Opto 22
form #1182.)
Nominal Range and Over-range Limits
All SNAP analog input modules have a nominal range for the
field signal and most support a 10% over-range limit. The
nominal range is the normal range of the field signal for the
module or point configuration. The over-range limit is the
maximum valid field signal the module or point configuration
can read outside of the nominal range. For example, the over-
range limits for the SNAP-AIV are -11 and +11 VDC, and for the
SNAP-AIVRMS, the over-range limit is 275 VAC.
Transformer isolation prevents ground loop currents from
flowing between field devices and causing noise that
produces erroneous readings. Ground loop currents are
caused when two grounded field devices share a connection,
and the ground potential at each device is different.
Isolation also protects sensitive control electronics from
industrial field signals.
Some modules or point configurations do not support field
signals outside of the nominal range. For example, points
configured as temperature inputs (thermocouple, RTD, ICTD)
do not support over-range readings.
IMPORTANT: Since these analog input modules provide
multiple single-ended input channels with a common
reference, the channels are not isolated from each other. (See
Opto 22 form #1182 for isolated modules.)
When the field signal is outside of the over-range limits of the
module, the brain will not be able to determine if the value is
too high or too low, so it will return an "out of range" value of -
32768.0
Bipolar and Unipolar Input Modules
Most SNAP analog input modules are considered to be
bipolar, which means the range extends equal amounts above
Over-range limits only apply to input modules. Output
modules are limited to their nominal ranges.
Opto 22 • 43044 Business Park Drive • Temecula, CA 92590-3614 • www.opto22.com
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© 2001–2014 Opto 22. All rights reserved. Dimensions and specifications are subject to change. Brand or product names used herein are trademarks or registered trademarks of their respective companies or organizations.
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