Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 170)

170 Publication 1756-UM009C-EN-P - December 2010
Chapter 8 Isolated Analog Output Modules (1756-OF6CI and 1756-OF6VI)
Clamping/Limiting
Clamping limits the output from the analog module to remain within a range
configured by the controller, even when the controller commands an output
outside that range. This safety feature sets a high clamp and a low clamp.
Once clamps are determined for a module, any data received from the
controller that exceeds those clamps sets an appropriate limit alarm and
transitions the output to that limit but not beyond the requested value.
For example, an application may set the high clamp on a module for 8V and
the low clamp for -8V. If a controller sends a value corresponding to 9V to the
module, the module will only apply 8V to its screw terminals.
Clamping alarms can be disabled or latched on a per channel basis.
To see how to set the clamping limits, see page 223 .
Clamp/Limit Alarms
This function works directly with clamping. When a module receives a data
value from the controller that exceeds clamping limits, it applies signal values
to the clamping limit but also sends a status bit to the controller notifying it
that the value sent exceeds the clamping limits.
Using the example above, if a module has clamping limits of 8V and -8V but
then receives data to apply 9V, only 8V is applied to the screw terminals and
the module sends a status bit back to the controller informing it that the 9V
value exceeds the module’s clamping limits.
To see how to enable all alarms, see page 223 .
IMPORTANT
Clamping is only available in floating point mode.
Clamp values are in engineering scaling units and are not
automatically updated when the engineering high and low
scaling units are changed. Failure to update the clamp values
may generate a very small output signal that could be
misinterpreted as a hardware problem.
IMPORTANT
Limit alarms are available only in floating point mode.