Allen-Bradley Micro800 General Instructions Manual page 577

Input parameters
Variable
AutoMode
Initialize
My_Gains
My_Gains.DirectActing
My_Gains.ProportionalGain
My_Gains.TimeIntegral
My_Gains.TimeDerivative
My_Gains.DerivativeGain
AutoTune
ATParameters
Load
Deviation
Step
ATDynaSet
ATReset
Output parameters
Parameter
AbsoluteError
Auto-tune parameters
The following table describes the variables that are used with each parameter in
the example to configure auto-tuning.
Parameter Description
Auto The operation mode of the PID controller:
TRUE - controller runs in normal mode.
FALSE – derivative term is ignored forcing the controller output to track the feedback within the
controller limits, and allowing the controller to switch back to auto without bumping the output
Initialize Initializes AutoTune sequence.
A change in value from TRUE to FALSE or FALSE to TRUE causes the controller to eliminate any
proportional gain during the cycle.
Gains Establishes the Gains PID for IPIDController.
DirectActing Defines the type of acting for the output.
TRUE - direct acting in which the output moves in the same direction as the error. That is, the actual
process value is greater than the SetPoint and the appropriate controller action is to increase the
output. For example, chilling.
FALSE - reverse acting in which the output moves in the opposite direction as the error. That is, the
actual process value is greater than the SetPoint and the appropriate controller action is to decrease
the output. For example: heating.
ProportionalGain Proportional gain for PID (>= 0.0001).
TimeIntegral Time integral value for PID (>= 0.0001).
The tendency for oscillation increases with a decrease in ti.
TimeDerivative Time derivative value for PID (> 0.0).
Damping increases with an increase in derivative time, but decreases if the derivative time value is too
large.
Derivative gain for PID (> 0.0).
When set to TRUE and Auto and Initialize are FALSE, the AutoTune sequence is started.
• Initial output value during auto-tuning.
• Allows the process value to stabilize at the load
• The standard deviation for a series of stabilized process values. For example, if the process value stabilized between 31.4 to 32.0,
then the deviation value would be (32.0-31.4)/2 = 0.3.
• Some process values, such as temperature, take a very long time to stabilize.
• The auto-tune process considers how the process value reacts to the changes in step value and derives the Gain parameters.
• Allocated time for the auto-tune to complete. It must be longer than what is required for the auto-tune process.
• A common value for many systems is 600 seconds, but some systems may require more time.
• If TRUE, the output will be reset to "0" after auto-tune completes.
• If FALSE, the output will remain at the load value after auto-tune completes.
Description
Absolute error (Process – SetPoint) from the controller.
Rockwell Automation Publication 2080-RM001D-EN-E - February 2015
Proportional Integral Derivative (PID) instruction
Chapter 20
577