(STC=2,MAN→AUT) Auto-startup end
Tuning end MI signal
application
Block status “STUP” Waiting for settling
(30 seconds)
Figure 1.13.5-3 Example of the Auto-Startup Action in Astatic (Integral) System
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Abnormal Termination of Auto-Startup
The following section explains the abnormal termination of auto-startup.
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Causes of the Abnormal Termination of Auto-Startup
The auto-startup action is terminated abnormally if the following events occur: • Power failure
• Change in the self-tuning operating mode (STC operating mode)
• Change to a block mode other than automatic modes (AUT, CAS, RCAS). • Failure to create an estimated process model
• The measured signal change (ΔPV) remains under 0.5 % of the MV Impulse amplitude (MI) after the maximum observation time (90 minutes) elapsed.
• Insufficient information from step response.
• The data status of the manipulated output value (MV) changes to CLP or CND. • The alarm status changes to IOP+, IOP-, OOP or CNF.
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Self-Tuning PID Controller Block (PID-STC) upon Abnormal Termination of
Auto-Startup
When the auto-startup action is stopped, the following changes take place inside the Self-tun- ing PID controller block (PID-STC):
• The block changes to automatic (AUT) mode.
• The STC operating mode changes to PID parameter display (STC=0). • The block status changes to auto-startup abnormal termination (PVER).
The block status changes or set the STC operating mode operation stop (STC=-1) cancels the auto-startup abnormal termination status.
IMPORTANT
Do not use auto-startup for systems whose process dead-time is short. This is because an abnormal termination processing of the auto-startup may not be carried out if the process dead-time is 4 seconds or less. If an abnormal termination processing could not be carried out, the block status remains as STUP.
If an auto-startup has been used by mistake, change the block mode to MAN mode and inter- rupt the auto-startup.
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Setup Items for Auto-Startup
The following items must be set in the auto-startup mode: • Control target type (OS)
Specify the type of response waveform to be targeted by the self-tuning function (STC function)
Select a target suitable for the controlled plant • MV Impulse amplitude (MI)
Set a value that may trigger the process variable (PV)’s impulse response around 5 %. • Control method (P, I, D)
Specify a desired control method
Specify one of the following three types of control methods: I control : P=0
PI control : P≠0, D=0 PID control : P≠0, D≠0
Within the range allowed by the process, the bigger the impulse response from the process variable (PV) the more accurate estimation can be provided by the model.
When a control algorithm that uses derivative (D) action is selected, it may change to the con- trol method that does not use derivative (D) action if it is judged appropriate by the STC func- tion.
1.13.6
On-Demand Tuning
On-demand tuning is applied to tune PID parameters (P, I, D) when tuning request is given from the operator. On-demand tuning may be applied to the loops where the change of set- point values need to be avoided.
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Execution of On-Demand Tuning
For on-demand tuning, when a tuning demand is given from the operator, a step test signal is added to the manipulated output value (MV) in a closed loop. Then the self-tuning is per- formed based on the response waveform of the corresponding process variable (PV). The method of on-demand tuning is shown below. To execute on-demand tuning, the follow- ing conditions must be satisfied:
• The self-tuning operating mode (STC operating mode) is the PID parameter display or PID automatic updating mode
• The block mode is one of the automatic modes
IMPORTANT
Before changing to the on-demand tuning mode, confirm that the value of the MV Impulse amplitude (MI) is well within the safe range.
When the STC operating mode is changed to on-demand tuning in the above state, on-de- mand tuning may be executed.
During on-demand tuning, the following actions take place:
1. Step signal equivalent to the MV Impulse amplitude (MI) is added to the manipulated out- put (MV) in the direction of decreasing deviation.
If the process type is “astatic system (IP=1),” the pulse of TR/5 in time span will be add- ed.
2. After the step signals is added, the STC operating mode returns to “0” or “1” in the next control period.
3. The response waveform of a measured signal that corresponds to the step change is monitored.
4. PID control and self-tuning are started.
MV Set as “STC=3” (on-demand command) Time Tuning PV
Figure 1.13.6-1 Responses in the On-Demand Mode
If responses from the process are extremely monotonous, an estimated model may not be created. In this case, increase the MV Impulse amplitude (MI) and retry the self-tuning.
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Setup Item for On-Demand Tuning
MV Impulse amplitude (MI): Set a value that may trigger the process variable (PV)’s im- pulse response around 5 %.
Within the range allowed by the process, the bigger the impulse response from the process variable (PV) the more accurate estimation can be provided by the model.
1.13.7
Tuning Parameters of Self-Tuning PID Controller
Block (PID-STC)
This tuning parameters of PID-STC block consist of three types; Setting parameters that may be set on the tuning view; Parameters for indication and the parameters defined on the Func- tion Block Detail Builder.
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Tuning Parameters
The tuning parameters of the Self-Tuning PID Controller Block (PID-STC) include the follow- ing types:
• Parameters may be set on tuning view
These tuning parameters can be set on the tuning view during operation. • Parameters for indication
These parameters are displayed in the tuning view to indicate the operating status of the STC function. The values of the parameters are calculated automatically by the Self-tun- ing PID Controller Block (PID-STC).
• Parameters defined on the Function Block Detail Builder
These parameters are defined on the Function Block Detail Builder.
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Parameters Set from the Tuning View
The table below shows the parameters that are set from the tuning view:
Table 1.13.7-1 Parameters Set from the Tuning View
Symbol Name Entry en- able/ disa- ble(*1) Range Default
Setup items in each operating mode(*2)
-1 0 1 2 3
STC STC operatingmode selection
switch x -1, 0, 1, 2, 3 0 (*3) (*4)
TR Process 95 %response time x 1 to 10000 sec-onds 40 sec-onds - ● ● xx ● NB Noise band x 1.0 to 20.0 % ofthe PV value (*5) 1.0 %(*5) - ● ● xx ● OS Control targettype x 0, 1, 2, 3 2 - ● ● ● ● MI MV Impulseamplitude x 0.0 to 20.0 % ofthe MV value (*6) 5.0 %(*6) - - - ● ● P Proportionalband x 0.0 to 1000.0 % 100.0 % ● ● xx xx xx I Integral time x 0.1 to 10000.0seconds 20.0 sec-onds ● ● xx xx xx D Derivative time x 0.0 to 10000.0seconds 0.0 sec-ond ● ● xx xx xx PMAX Proportionalband high limit x 0.0 to 1000.0 % 1000.0% - ● ● xx ● PMIN Proportionalband low limit x 0.1 to 1000.0 % 0.1 % - ● ● xx ● IMAX Integral timehigh limit x 0.1 to 10000.0seconds 10000.0seconds - ● ● xx ● IMIN Integral timelow limit x 0.1 to 10000.0seconds 0.1 sec-onds - ● ● xx ●
Symbol Name Entry en- able/ disa- ble(*1) Range Default
Setup items in each operating mode(*2)
-1 0 1 2 3
DMAX Derivative timehigh limit x 0.0 to 10000.0seconds 2000.0seconds - ● ● xx ● PIDC PID update ra-tio coefficient x 0.00 to 1.00 1.00 - - ● - - *1: x: Can be entered from the tuning view at any time.
*2: ●: Setting required. -: Setting not required.
xx: Setting is done automatically, but can be entered from the tuning view, as well.
*3: The default values of the 11th and subsequent PID-STC controller blocks within the same control station will be -1. *4: A determining factor of the operating mode.
*5: A percentage value converted from the PV engineering unit data. *6: A percentage value converted from the MV engineering unit data.