Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 152)

152 Publication 1756-UM009C-EN-P - December 2010
Chapter 7 Non-isolated Analog Output Modules (1756-OF4 and 1756-OF8)
Open Wire Detection
This feature detects when current flow is not present at any channel. The
1756-OF4 and 1756-OF8 modules must be configured for 0…20 mA
operation to use this feature. At least 0.1 mA of current must be flowing from
the output for detection to occur.
When an open wire condition occurs at any channel, a status bit is set for
that channel.
For more information on the use of status bits, see page 159 .
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 .
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.