Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 151)

Publication 1756-UM009C-EN-P - December 2010 151
Non-isolated Analog Output Modules (1756-OF4 and 1756-OF8) Chapter 7
Ramping/Rate Limiting
Ramping limits the speed that an analog output signal can change. This
prevents fast transitions in the output from damaging the devices that an
output module controls. Ramping is also known as rate limiting.
The maximum rate of change in outputs is expressed in engineering units per
second and called the maximum ramp rate.
See page 223 for how to enable Run mode ramping and set the maximum
ramp rate.
Hold for Initialization
Hold for Initialization causes outputs to hold present state until the value
commanded by the controller matches the value at the output screw terminal
within 0.1% of full scale, providing a bumpless transfer.
If Hold for Initialization is selected, outputs hold if there is an occurrence of
any of these three conditions.
• Initial connection is established after power-up.
• A new connection is established after a communications fault occurs.
• There is a transition to Run mode from Program state.
The InHold bit for a channel indicates that the channel is holding.
To see how to enable the Hold for Initialization bit, see page 220 .
Types of Ramping
Ramping Type Description
Run mode ramping This type of ramping occurs when the module is in Run mode
and begins operation at the configured maximum ramp rate
when the module receives a new output level.
IMPORTANT: This is only available in floating point mode.
Ramp to Program mode This type of ramping occurs when the present output value
changes to the Program value after a Program command is
received from the controller.
Ramp to fault mode This type of ramping occurs when the present output value
changes to the Fault value after a communication
fault occurs.