Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 81)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 81
1756-OF8H HART Analog Output Module Chapter 6
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.
Table 15 describes the types of ramping that are possible.
The maximum rate of change in outputs is expressed in engineering units per
second and called the maximum ramp rate.
For additional information about ramp rate, see Chapter 7 , Configuring the
Modules, which describes how you can set Ramp Rate on the output Limits
dialog box.
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 terminal within
0.1% of full scale, providing a bumpless transfer.
If Hold for Initialization is selected, outputs hold if any of these 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.
The ChxInHold bit for a channel indicates that the channel is holding.
Table 15 - Ramping Types
Ramping Types Description
Run mode ramping This type of ramping occurs when the module is in Run mode and limits
the rate at which the output changes from one commanded value
to another.
Ramp-to-Program mode This type of ramping occurs when the controller is placed in the
Program mode. The present output value changes to the Program Value.
If the connection to the module is inhibited, the Program mode value
and ramp rate are applied.
Ramp-to-Fault mode This type of ramping occurs when there is a communication or
controller fault. The output signal changes to the fault value after a
communication fault occurs.