User Manual

Rockwell Automation Publication 1756-UM005B-EN-P - January 2013 47
Module Features Chapter 3
Ramping/Rate Limiting
Ramping limits the speed at which 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. Ramping is possible in
the following situations:
•Run mode ramping—Occurs during Run mode and begins operation at
the configured maximum ramp rate when the module receives a new
output level.
•Ramp to Program mode—Occurs when the present output value
changes to the Program Value after a Program Command is received from
the controller.
•Ramp to Fault mode—Occurs when the present output value changes to
the Fault Value after a communication fault occurs.
The maximum rate of change in outputs is expressed in engineering units per
second and called the maximum ramp rate. To see how to enable ramping and
set the maximum ramp rate, see page 78
.
Hold for Initialization
Hold for Initialization causes outputs to hold their 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 when any of the three
conditions occur:
• Initial connection is established after powerup.
• A new connection is established after a communication fault occurs.
• There is a transition to Run mode from Program state.
To see how to set the Hold for Initialization, see page 77
.
Open Wire Detection—Current Mode Only
This feature detects when current flow is not present at any output channel. 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 49
.
IMPORTANT
This feature is only active with the 0…21 mA output range.