User Manual Instruction Manual

Rockwell Automation Publication 2080-UM001D-EN-E - September 2012 105
IPID Function Block Appendix D
How to AutoTune
Before you continue, be sure that:
• the system must be a stable system
• the "Auto" input to the IPIDCONTROLLER is set to false
• AT_Param is set. The input Gain and DirectActing must be set according
to the process and DerivativeGain set, typically, to 0.1.
To auto tune, perform the following steps:
1. Set the "Initialize" input to "TRUE".
2. Set the "AutoTune" input to "TRUE".
3. Wait for the “Process” input to stabilize or go to steady state.
4. Change the "Initialize" input to "FALSE".
5. Wait until the "ATWarning" output value changes to"2".
6. Get the tuned value from "OutGains".
Step REAL Step value for AutoTune. Must be greater than noise band and less
than ½ load.
ATDynamSet REAL Auto Tune time. Set the time to wait for stabilization after the step
test (in seconds). Auto Tune process will be stopped when
ATDynamSet time expires.
ATReset BOOL Determines whether the output value is reset to zero after an
AutoTune sequence:
• True – Reset IPIDCONTROLLER output to zero after Auto tune
process.
• False – leaves output at load value
(1) The application engineer can estimate the value of ATParams.Deviation by observing the value of Proces input.
For example, in a project that involves the control of temperature, if the temperature stabilizes around 22 °C,
and a fluctuation of 21.7…22.5 °C is observed, the value of ATParams.Deviation will be (22.5-21.7)/2=0.4.
IMPORTANT
To finalize the tuning, some fine tuning may be needed depending on the
processes and needs. Autotune will provide suboptimal value of tuning. It
may be necessary to do fine tuning with the values, in close loop, to
achieve the user goal.
If ATWarning goes to -2 to indicate Auto Tune unsuccessful, you may
need to adjust the AT_Param and/or scan time.
AT_Param Data Type
Parameter Type Description