The PID could be replaced with an adaptive Integral Action controller (AIA). To maintain stability even in the presence of parametric interceptions, adaptive integral control utilizes proportional-integral control and dynamic gains calculations. When delays in the controlled process cause integral windup, undershoot or overshoot leads to instability, this control works better than PID.
Figure 1: Aia Function Block |
Figure 2: Aia Property Sheet |
Figure 3: Aia Logic Diagram
Err = Sensor-Set Point.
The Err term is set to - Err if Direct or Reverse is set to reverse. The Function Block keeps track of the old proportional error from iteration to iteration. This is cleared when you power up or reset
Inputs
Input Name |
Description |
Controlled Value |
Input from the sensor present value (Temperature, Pressure etc.) |
Setpoint |
It is 32-Bit floating set point. Which used to maintain the controlled value. |
Throttling Range (In & Par) |
Its same as propotional band. Output Rate of change in value will be decided based on error and Throttling Range deviation. If the error value is equal to the throttling Value then rate of change in output will be the maximum value per sec. If the error value is 50% of the Throttling Value then the rate of change in output will be the mid value between the minimum and Maximum value per sec. |
Deadband (In & Par) |
Deadband is the absolute value that Error must be greater than before the output will change. EffErr = Err-deadband. If Err > 0, ErrSign = 1 else ErrSign =-1. If |Err| < dead band, then AbsErr = 0. Otherwise (|Err| > deadband), AbsErr = |Err|-deadband. Output = Output + ErrSign * [(maxAOchng - minAO) * (AbsErr / (ThrottlingRange - Deadband)) * 3 + MinAO)]. |
Max Chg Per Sec (In & Par) |
This is the maximum amount (%) that Output will change for a single cycle of the control. This is set to 100 % / (Actuator speed (second/full stroke))/ (DDC cycles per second). Example: 100%/150 sec/2=0.333% per sec. |
Derivation Gain (In & Par) |
It gives a controller additional control action when the error changes consistently. It also makes the loop more stable (up to a point) which allows using a higher controller gain and a faster integral. |
Min Chg Per Sec (In & Par) |
This is the minimum amount (%) that Output will change for a single cycle of the control, if the setpoint is not reached. |
Operation (In & Par) |
Direct: "0" = Direct If the CV >SP then the calculated output value will vary from 0-100%. Example: Cooling Reverse: "1" = Reverse If the CV <SP then the calculated output value will vary from 0-100%. Example: for heating and pressure application. Off "2": operations will stop |
Table 1: Inputs of Aia Function
Outputs
Output Name |
Description |
Out |
Output = Output + ErrSign * NonLin (AbsErr, ThrottlingRange, MaxAOchange, MinAOchange) |
Stop |
It is a boolean point. If it is set to "true", block will disable Aia function block. If it is set to "false", it enables Aia function block. |
Table 2: Outputs of Aia Function
Parameters
Parameter Name |
Description |
Throttling Range Par (In & Par) |
If Throttling Range is "null", Throttling Range Par is used as parameter. |
Deadband Par (In & Par) |
If Deadband is "null", Deadband Par is used as parameter. |
Max Chg Per Sec Par (In & Par) |
If Max Chg Per Sec is "null", Max Chg Per Sec Par is used as parameter. |
Derivative Gain Par (In & Par) |
If Derivative Gain is "null", Derivative Gain Par is used as parameter. |
Min Chg Per Sec Par (In & Par) |
If Min Chg Per Sec is "null", Min Chg Per Sec Par is used as parameter. |
Operation Par (In & Par) |
The operation specifies the direction of the controller, e.g. a different direction is necessary in heating mode than in cooling mode. There are three operations:
|
Out Save |
Master Sync Enabled : If you set it to "true" the last output will be set as output for one cycle after the controller restarts. The application can use it to return to the same state before the controller restart. Out: To enable or disable the Out Save feature. |
Table 3: Parameters of Aia Function
Examples
1. Aia with Direct operation:
Figure 4: Aia with Direct Operation
Figure 5: Aia with Direct Operation - Property Sheet
2. Aia with Reverse operation:
Figure 6: Aia with Direct Operation
Figure 7: Aia with Direct Operation - Property Sheet
Refer to General for general information about IRMN4 Function Blocks.