Rockwell Automation 1769-OF4VI Compact I/O Isolated Analog Modules - Manual (Page 62)

Publication 1769-UM014B-EN-P - May 2010
4-10 Module Data, Status, and Channel Configuration for the Output Modules
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 1769-OF4CI module
for 15 mA and the low clamp for 5 mA. If a controller sends a value
corresponding to 16 mA to the module, the module will only apply 15 mA to
its screw terminals.
Clamping is disabled on a per channel basis by entering a 0 value for both the
high and low clamps in the Configuration Data file. Interrupts are generated
on a high- or low-alarm by setting (1) the SIO bit (for high-clamp or
over-range alarm) or setting (1) the SIU bit (for low-clamp or under-range
alarm). Alarms caused by exceeding over-/under-range or clamp limits can be
latched by setting (1) a channel’s LA bit on a per channel basis.
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
at the clamping limit but also sends a status bit to the controller notifying it
that the value sent exceeds the clamping limits.
With reference to the example in the Clamping/Limiting section, if a
1769-OF4CI module has clamping limits of 15 mA and 5 mA but then
receives data to apply 16 mA, only 15 mA is applied to the screw terminals.
The module sends a status bit back to the controller informing it that the 16
mA value exceeds the module’s clamping limits.