EBSILON®Professional Online Documentation
EBSILON Professional Components / Components - General and Categories / Controllers / Component 12: Controller with external target value
In This Topic
    Component 12: Controller with external target value
    In This Topic

    Component 12: Controller with external set target value


    Specifications

    Line connections

    1

    Reference value - process value

    2

    Actual value

    3

    Correction value - controlled value

    The colour indicates the type of activation of the controller (depending upon the flag FACT):

    Dark purple:             controller starts immediately

    Red:                          delayed start after 20, 30, 40 or 50 iterations

    Pink:                         delayed start after 100 iterations

    White:                      controller is deactivated
     

    General       User Input Values       Characteristic Lines       Physics Used       Displays       Example 

    General

    Generally, the aim of a controller (component 12) is to modify an "actual / process value" by changing the "controlled value", until the "scheduled / target value / set point" is reached.

    Depending on the complexity of the controlling task, you can select between three types of controllers:

    For all controllers, you have to specify the type of the controlled value and the type of the process  value. The type of the controlled value must be a basic quantity (pressure, enthalpy or mass flow). The type of the process value can be a derived quantity, such as the temperature or the heat flow, or a fraction of a chemical composition. In the latter case, you must specify the substance, on which the controlling will be based.

    An important flag is the characteristic of the controller. It defines the direction, in which the correction value is to be modified:

    A start value has to be specified for the controlled value, either internally as the specification value or externally via the component 33 (start value).

    The start value should be at least in the order of magnitude of the expected value and not several powers of ten off. The recommended procedure is to get the model running without a controller first, then you will get suitable start values.

    Note that controllers often are critical to the convergence of your calculation, especially if there are several controllers that work against each other. There are certain flags to tune the convergence behaviour by damping or delayed activation of the controller.

    Controllers can be damped even more strongly as of Release 9 this, three more damping levels ("very very high”, "even higher”, ”extremely high") have been introduced.

    When you perform a data validation, you should avoid conflicts with controllers.


    With all controllers, a new mode of calculation with an improved integration of the control into the equation system has been implemented. In particular, problems occurring in the case of controls near the value 0 have been fixed. 
    The new mode of calculation is globally activated and deactivated, respectively, for all controllers in the model settings (simulationcontroller). In many cases it is possible to do without relaxations and dampings when using the new controller mode. 
    As in many cases controllers are the cause of convergence problems, controllers are often switched off first to analyze these problems. This had to be done individually for each controller. It is possible to carry out global settings for activating the controllers.

       - Activation of the controllers only from a certain iteration step on
       - Activation of the controllers only after reaching a certain degree of convergence 

    In any case, the activation of a controller will be effected only when this is also provided by the individual specifications at the controller. In particular, switched-off controllers will remain switched off.


    The sequence of the specification values in the input screen has been sorted. First are the specification values that relate to the reference value, and then the values that relate to the correction variable. Then follow general controller parameters like characteristic, activation, start value specification, and damping or limitation of change.

    Decoupling of turn-on/-off feature and delayed start 


    The flag FACT served both to turn a controller on and off, and to specify a delayed start. In order to be able to better expand the setting options, this feature has been distributed to the two flags FACT and FFU.
    The flag FACT is used to specify at which iteration step the controller is to start (at the earliest). FACT=0 means that the controller is to start as early as possible. The variants FACT=-1 and FACT=-2 for deactivating the controller with (-1) and without (-2) start value setting respectively have been marked as “deprecated“, but they are still operational for reasons of compatibility. However, it is recommended to use the new flag FFU for this purpose.
    The flag FFU offers various variants for activating and deactivating controllers in different load cases. There are e. g. the following setting options :

    • Controller active
       - always: FFU=1  
       - only in design case: FFU=4 or -4
       - only in off-design case: FFU=5 or -5
       - never: FFU=0 or -1

    • Controller not active (i.e. does not control) but sets its start value
       - always: FFU=0 
       - only in design case: FFU=5
       - only in off-design case: FFU=4

    • Controller not active, without start value setting
       - always: FFU=-1 
       - only in design case: FFU=-5
       - only in off-design case: FFU=-4

    As of release 11, there is an alternative start value L2STARTOFF (component 39) or L3STARTOFF (components 12 and 69), which is used when the controller is switched off but should set its start value.

    Alternative start value in the case of deactivated controller


    The start value one wants to set with deactivated controller is not always suitable as start value in the case of activated controller (e.g. 0 kg/s). You then had to set different starting values in the different profiles. As of release 11, there is an alternative start value L2STARTOFF (Component 39) and L3STARTOFF (Components 12 and 69) respectively for this. It is used when the controller is deactivated but is to set its start value. If no value is entered here, L2START and L3START respectively will be used also in the case of deactivated controller.

    Compliance with limits

    The limits L2MIN/L2MAX (Component 39) and L3MIN/L3MAX (Component 12, Component 69) respectively were not strictly adhered to, but only caused the controller to be deactivated when the respective limit was exceeded. This mainly served to prevent a drifting off in the course of the iteration. For the final result, however, this behaviour is unsatisfactory as the precise achieved value depends on the behaviour of the iteration.
    For this reason, from Release 11 the limits are strictly complied with. For reasons of compatibility, however, it is possible to switch back to the old behaviour via the flag FLIM. For this, FLIM has to be set to 0 (“Shut off controller after limit was exceeded“). The standard setting is FLIM=1 (“Stop at limit“).

     

    Functionality of the limits

    The limits L3MIN/L3MAX (Component 12, Component 69) and L2MIN/L2MAX (Component 39) only become effective if numerical values are specified for them.

    If that is the case, the flag FLIM checks according to the specification with
    FLIM=0: the controller is switched off after the limit L3MIN/L3MAX is fallen below / transgressed
    or with
    FLIM=1: the controller stops on the limit L3MIN/L3MAX.

    Examples of the functionality of L3MIN, L3MAX and FLIM see Controller component 39 (EBSILON®Professional,Online Help).

     

    Deactivation of warnings


    A warning is issued by default when the controller cannot achieve its target value. In some cases, however, this is unnecessary, e.g. when, in the case of an injection, the inlet temperature is already below the set point temperature. In such cases it is possible to shut off the warning with the flag FWARN.
    The flag FWARNOFF allows to activate or deactivate warnings for deactivated controllers. Here it is checked if the start value (in the case of component 69 also the off-value L3OFF) is within the range of validity.

     

    Start Value Transfer In controllers (FMODE)

     

    (Components 12, 39, and 69) it is possible to take over the result for the control variable as start value for the next calculation. As there is a certain analogy with respect to the transfer of the reference values for off-design calculations here, the flag for this has been named FMODE as well. The following settings exist:

    The transferred value is written onto the specification values L3START and L3STARTOFF. However, it only has an impact if FL3START is set to “internal start value specification“. Also, the transfer only takes place if a value was entered into L3START respectively before. If the field has been set to the “empty”, the field will remain empty. When adding new controllers, FMODE=1 will be set by default. In a good modeling, the final result should in fact not (or only slightly) depend on the start value, but a change of the start value may lead to convergence problems. An influence on the final result also arises from the interaction of controllers with threshold values and limit values if it depends on the convergence behaviour when a controller is activated and deactivated respectively.

    Flag FWARN

    In the controllers there is a flag FWARN that allows setting in which situations the controller is to output warnings. For this there is a new setting FWARN=3.
    With this setting, a warning is only output if the controller has not reached its target but the control variable has not reached its limit value either.

    This setting makes sense  if reaching the limit value represents a “normal” condition, like e.g. in the case of an injection where a certain temperature is to be set downstream
    of the injection. By the injection, however, only a reduction of the temperature can be effected. If the temperature is below this set point value, nothing needs to be injected.
    FWARN=3 allows to set that in this case no warning is to be effected. The control variable of the controller then equals the lower limit value of 0 kg/s, and no warning is output
    if the set point value of the temperature has not been reached.

    It is possible to output an error message instead of a warning with the setting FWARN=4.

    FWARN=5 allows to individually program in a Kernel expression EWARN under which circumstances a comment, a warning or an error message is to be output.

     

    Control Precision

    For the solution of an equation system, Ebsilon continues the iteration as long as the changes from one iteration step to the next are smaller than the specified iteration precision.
    Here the termination of the iteration is independent of to what extent the controllers have reached their set point value. Only a warning will be output if the deviation between
    actual value and set point value is too great.

    In the case of strongly damped controllers in particular, the change from one iteration step to the next is relatively small, so that the convergence criterion is already fulfilled although
    the control target has not been achieved yet. In these cases it would be desirable if the iteration were continued for another couple of steps in order to get closer to the specified target. Therefore in Release 12 the possibility to prevent a termination of the iteration in the case of too great a deviation from the set point value has been created.

    Inversely, there are also cases where the adjustment of an unimportant variable requires very many iteration steps and thus increases the computing time for the entire model. In such
    cases it is desirable to be able to carry out the control with a greater fuzziness.

    This option is available with the specification value TOL (for all controllers).

    The specification value TOL is used for setting the control precision in both cases. Which one of the two cases is desired is set via the flag FTOL:

    FTOL=1 (“TOL=lower bound“) serves to accelerate the control by means of a greater fuzziness. In this case, the controller terminates the control if the relative deviation between actual
    value and set point value falls below the bound TOL.

    FTOL=2 (“TOL=upper bound“) prevents the termination of the iteration as long as the relative deviation between actual value and set point value transgresses the bound TOL. However,
    this does not apply if the correction variable has reached its lower or upper bound. As the controller does not continue operating in this case, carrying out further iteration steps does
    not make sense.

    For analyzing the convergence behaviour, in the case FTOL=2 you can see in the result value ITNOTCONV up to which iteration step the controller has prevented a termination of the
    iteration. This allows to systematically find out the controllers that are responsible for a deterioration of the convergence behaviour and to improve their settings if necessary.

    FTOL=0 is the default setting.

    Zero point Shift

    As in the case of controllers in Ebsilon the change of the actuating variable is effected via a change factor, controllers previously could not be operated in such a way that the actuating variable was able to change its algebraic sign. To enable this, there is now a specification value CZP that serves to shift the zero point of the controller internally. Shifting is effected in positive direction. If e.g. “100“ is entered, -100 will be mapped onto 0 and it will also be possible to control beyond 0 in the range >-100.

    With great values of CZP, the internal actuating variable will become great accordingly so that this way, in the case of similar relative changes, the absolute change of the actuating variable will become very great too. This may lead to convergence problems. In this case, it is recommended to decrease the maximum change factor (CHL3 respectively), and that from the beginning ( ITCHL3 = 0 respectively).

    Kernel Expressions for Range Limits

    Previously, only fixed values could be entered as range limits for the actuating variable. Now it is possible to use a Kernel expression as the limit. To do so, the corresponding flag (FL3MIN and FL3MAX respectively for Components 12 and 69) has to be set to “Kernel expression“, and an EbsScript that calculates the corresponding limit has to be created in EL3MIN and EL3MAX respectively for Components 12 and 69.

    This feature was needed for the variation of the steam inlet pressure for a preheater in order to achieve a certain feed water outlet temperature. Without limitation, the controller decreased the pressure so far that the saturated water temperature dropped below the feed water inlet temperature and no condensation was possible anymore. A fixed limit, however, was not possible either as the feed water inlet temperature is not known in advance but only appears in the course of the calculation. For instance, the following Kernel expression allows to set the lower pressure limit to a reasonable value in each iteration step:

    function evalexpr:REAL;

    begin

        evalexpr:=waterSteamTable(1006, Feedwater.T, 0.0);

    end;
     

    Note - Setting a relative humidity of 100% or super saturation in air and flue gas lines   

    To a relative humidity of for example, to set 100% or super saturation, a controller is required.

    In the previous handling with the function "air humidity (rel.)", It could happen after iteration course that the air was supersaturated, i. Water contained in the liquid phase. The reason for this was that even with supersaturated air, the relative humidity remained at the value of 100% and the controller had thus reached its set point.

    In order to allow a regulation to the saturation point (100%) or the setting of a certain super saturation, there is a function "saturation factor".

     

    The saturation factor always refers to the maximum possible proportion of gaseous water. If the water content is higher, you get liquid water XH2OL. Humid air can only be considered approximately as an ideal gas. With increasing water content, the real proportion of gaseous water XH2OG decreases again. In the ideal approximation, the proportion of gaseous water would then simply remain constant, no matter how much liquid water would add to it. In reality, that's probably not the case and therefore with supersaturated air:                             

    XH2OG> X_SAT = f (p, t (air outlet line))

    For values up to 100%, the results of the "Saturation factor" function are the same as those of the "Humidity (rel.)" Function. 

    Definition Saturation factor for "saturated air" 0 - 100%: The result values agree with the results of the "relative humidity" function.

    Definition saturation factor for "supersaturated air"> 100% = corresponds to the ratio: total water content (XH2O) / maximum possible gaseous water content

    (Water vapour saturation concentration x_sat = f (p, t (air, port 2))

    Example: Application of saturation factor:

    See example "Saturation factor" in the chapter Component 39 "Controller  (internal set value)"  

     


    User Input Values 

    Controller Main Attributes

    FFU

    Flag for ON / OFF / SET-start-value

    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: OFF: No regulation, but initial value setting in all load cases
    =1: ON: Control active in all load cases
    =4: ON: Control active in the design, OFF (only starting value setting) in partial load
    =5: OFF (only starting value setting in the design, ON: control active in partial load
    = -1: OFF: Completely deactivated in all load cases
    =-4: ON: control active in the design, OFF: completely deactivated in partial load
    =-5: OFF: Completely deactivated in the design, ON: Control active in partial load
    =-6: OFF: initial value setting in the design; OFF: no start value setting in partial load
    =-7: OFF: start value setting in partial load; OFF: no initial value in the design

    NOTE on: -6 / -7: In both cases there is no regulation. Actually, the use of a controller is superfluous in this case, since the same effect could also be achieved with a measuring point (component 46) instead. However, it facilitates a uniform design of several circuits or the creation of generally usable macros if a control can be activated if necessary.

     

    FCHAR

    Flag for Controller characteristic   

    Like in Parent Profile (Sub Profile option only)

    Expression  

    =1:  Positive (i.e. an increase in the correction variable leads to an increase in the actual value)
    =-1: Negative (i.e. an increase in the correction value leads to a decrease in the actual value)

    Process Variable

    FL1L2

    Flag for Type of process variable (target and process value) 

    Like in Parent Profile (Sub Profile option only)

    Expression  

    =1: Pressure

    =2: Temperature

    =3: Enthalpy

    =4: Mass flow

    =5: Power/heat flow

    =6: Enthalpy of boiling liquid for given pressure

    =7: Enthalpy of saturated vapour for given pressure

    =8: Enthalpy of boiling liquid for given temperature

    =9: Enthalpy of saturated vapour for given temperature

    =10: Pressure of boiling liquid for given temperature


    =12: Steam content (X) of water/steam

    =13: Composition of the mass ratio (use with FSUBST)

    =14: Net calorific value

    =15: Composition as mole ratio (use of FSUBST) of all substances

    =16: Composition as mole ratio (use of FSUBST) of the dry part (without water/steam)

    =17: Entropy

    =18: Volume flow

    =19: Specific volume

    =20: Degrees sub cooling (with WD-lines this value refers to the boiling point, when humid air to the dew point temperature)

    =21: Degrees super heating (with WD-lines this value refers to the boiling point, when humid air to the dew point temperature)

    =22: Relative Pressure

    =23: Exergy, Note: Regarding the exergy, however, please be aware that the solution may not be unambiguous as the exergy does not
                         rise monotonously with  the temperature in all temperature ranges. Depending on the starting conditions and the set
                         characteristic, sometimes one and sometimes the other solution may be found.

    =24: Voltage
    =25: Current
    =26: Frequency              

     

    FSUBST

    Substance to be controlled (in combination with FL1L2 = composition)

    Like in Parent Profile (Sub Profile option only)
    Expression  

    =0:   nothing
    =-1: Humidity (rel.)
    =-2: Humidity (abs.)
    =1:   Nitrogen (N2)
    =2:   Oxygen (O2)
    =3:   Carbon dioxide (CO2)
    =4:   Water H2O
    =5:   Sulphur dioxide SO2
    =6:   Argon (Ar)
    =7:   Carbon monoxide CO
    =8:   Carbonyl sulfide (COS)
    =9:   Hydrogen (H2)
    =10: Hydrogen sulphide (H2S)
    =11: Methane (CH4)
    =12: Hydrogen chloride HCl
    =13: Ethane (C2H6)
    =14: Propane (C3H8)
    =15: Butane (C4H10)
    =16: n-Pentane  (CH3-CH2-CH2-CH2-CH3)
    =17: Hexane (C6H14)
    =18: Heptane (C7H16)
    =19: Acetylene (C2H2)
    =20: Benzene  (C6H6)
    =21: Elementary carbon (C)
    =22: Elementary hydrogen (H)
    =23: Elementary oxygen (O)
    =24: Elementary nitrogen (N)
    =25: Elementary Sulphur (S)
    =26: Elementary chlorine (Cl)
    =27: Ash
    =28: Calcium hydroxide (Ca(OH)2)
    =29: deprecated Water (liquid) (H2O)
    =30: Water bound (H2O)
    =31: Ash (gaseous)
    =32: Nitrogen monoxide (NO)
    =33: Nitrogen dioxide (NO2)
    =34: Ammonia NH3  
    =35: deprecated  Ammonia (liquid) (NH3)  
    =36: deprecated  Carbon dioxide  (liquid) (CO2)       
    =37: Methanol (Ca3OH)   
    =38: deprecated Water (H2O)             
    =39: Neon (Ne)
    =40: Dry Air

    further material properties No. 41 - No. 2400
    Further material values to be regulated for a composition can be found on the surface of the controller - default value "FSUBST"
    Obviously, or entering two to three significant letters of the desired material value is sufficient to obtain a targeted selection of material values.

     

    ADD

    Controller offset: <L2>=<L1>+ADD

    Controller Output

    FL3

    Controlled variable type

    Like in Parent Profile (Sub Profile option only)
    Expression 

    =1: Pressure
    =3: Enthalpy
    =4: Mass flow
    =5: Power
    =24:Voltage
    =26:Frequency

    FL3START

    Flag for the type of start value default                  

    Like in Parent Profile (Sub Profile option only)
    Expression 
          

    =0: internal default through specification value L3START

    =1: external default  (Stricter plausibility checks:, There will as of "Release 12" be error messages if 
                                      - FL3START respectively are set to “external start value specification“, 
                                        but no corresponding start value or measured value exists on the respective line.

                                      - a value is used as actuating variable that cannot be modified at all but is determined by other components. )

     

    L3START

    Start value for the controlled value (if FL3START=0)

    L3STARTOFF

    Alternative start value for controllers with FFU = 0 (optional)

    FLIM

    Handling of L3MIN and L3MAX
     Like in Parent Profile (Sub Profile option only)
    Expression 
         

    =0: Shut controller off after limit was exceeded

    =1: Stop at limit

    FL3MIN

    Source of minimum value of controlled variable

    Like in Parent Profile (Sub Profile option only)
    Expression 
          

    =0:Specification value L3MIN
    =2: Kernel expression EL3MIN

    L3MIN

    Minimum value for the controlled value :
    if while simulating the controlled value falls below L3MIN, then instead the value L3MIN is set and the simulation is continued.

    EL3MIN

    Function for  minimum value

    FL3MAX

    Source of maximum value of controlled variable

    L3MAX

    Maximum value for the controlled value :
    if while simulating the controlled value exceeds L3MAX, then instead the value L3MAX is set and the simulation is continued.

    EL3MAX

    Function for  maximum value

     

    Additional Attributes

    FACT

    Number of iterations after which the controller is activated 


    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: immediately

    =20: after 20 iterations

    =30: after 30 iterations

    =40: after 40 iterations

    =50: after 50 iterations

    =60: after 60 iterations

    =80: after 80 iterations

    =100: after 100 iterations

    =150: after 150 iterations

    =250: after 250 iterations

    =Deprecated: -1: controller deactivated, only setting the start value

    =Deprecated: -2: controller completely deactivated

    FDAMP

    Flag for strength of damping 

    Like in Parent Profile (Sub Profile option only)

    Expression

    =1: Without

    =2: Very little

    =3: Little

    =4: Medium

    =5: Medium high

    =6: High

    =7: Very high

    =8: Very very high

    =9: Even higher

    =10: Extremely high

    ITCHL3

    Number of iterations after which the change factor becomes active (default value: 100)

    CHL3

    Maximum change factor of corrected value

    (set as constant 0.15 till ITCHL3 is reached,

    after ITCHL3 according to the default between the limits: 0 < CHL3 <= 0.15)

    CZP

    Controller zero point

    STOPGRAD

    Stop controlling if gradient is less than

    ITSTEP

    Controller is active every n-th step (default value: 1)

    FSEQ

    Flag to define the position in calling sequence                 

    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: Parallel to other components

    =1: Late, after fluids are recalculated

    FSTOP

    Stop behaviour if controller has not started

    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: Do not stop iteration before controller has started
    =1: Stop in case of convergence even if controller has not started

    FTOL

    Flag for meaning of TOL 

    Like in Parent Profile (Sub Profile option only)

    Expression

    = 0: not used
    = 1: TOL= lower limit: controller is working only as long as relative deviation > TOL
    = 2: TOL= upper limit: relative deviation must be < TOL before iteration stops

    TOL

    Controller tolerance

    FMODE

    Flag for transfer of calculated value of controlled variable to start value

    Like in Parent Profile (Sub Profile option only)

    Expression

    =0 : After calculation in design mode

    =1 : No

    =-1: After each calculation

    Notification Options

                   

    FWARN

     

    Notification in case of missed target
    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: Not notification
    =1: Warning
    =3: Warning,  unless correction value is at limit
    =4: Error
    =5: Notification  according to EWARN
          FWARN=5 allows to individually program in a Kernel expression EWARN under which circumstances a comment, a warning or an error message is
          to be output.

    EWARN

    Function for notification

    function evalexpr:REAL;
    var
        target,actual,correction,errorlevel:real;
        diff:real;   
    begin
        target:=keGetInternal("TARGET");
        actual:=keGetInternal("ACTUAL");
        correction:=keGetInternal("CORRECTION");
        errorlevel:=keGetInternal("ERRORLEVEL");
       
        if (abs(target)>0) then
        begin //use relative deviation
         diff:=abs(actual-target)/target;
        end
        else
        begin  
         diff:=abs(actual-target);
        end;
       
        if (diff > errorlevel) then
        begin
         evalexpr := 3;  //Error
        end
        else if (diff > 0.1*errorlevel) then
        begin
         evalexpr := 2;  //Warning
        end
        else if (diff > 0.01*errorlevel) then
        begin
         evalexpr := 1;  //Comment
        end
        else
        begin
         evalexpr := 0;  //None
        end;
     end; 

    FWARNOFF

    Plausibility check in case of inactive controller
    Like in Parent Profile (Sub Profile option only)

    Expression

    =0: No warning if range (L2MIN to L2MAX) is exceeded

    =1: Warning if range (L2MIN to L2MAX) is  exceeded


     

    Generally, all inputs that are visible are required. But, often default values are provided.

    For more information on colour of the input fields and their descriptions see Edit Component\Specification values

    For more information on design vs. off-design and nominal values see General\Accept Nominal values

     

    Values for FL1L2

    Default value

    Actual value

    measured

    for comparison

    for comparison

    1

    2

    3

    4

    5

    Pressure

    Temperature

    Enthalpy

    Mass flow

    Heat flow

    Pressure

    Temperature

    Enthalpy

    Mass flow

    Heat flow

    Pressure

    Temperature

    Enthalpy

    Mass flow

    Heat flow

    6

    7

    8

    9

    10

    13

    14

    15

    16

    17

    18

    19

    20

    21

    Pressure

    Pressure

    Temperature

    Temperature

    Temperature

    Concentration (Mass)

    Net calorific value

    Mole fraction

    Mole fraction (mole, dry)

    Entropy

    Volume flow

    Specific volume

    Degrees sub cooling

    Degrees super heating

     

    Enthalpy'  (P)

    Enthalpy'' (P)

    Enthalpy'  (T)

    Enthalpy''  (T)

    Pressure' (T)

    Concentration (Mass)

    Net calorific value

    Mole fraction

    Mole fraction (mole, dry)

    Entropy

    Volume flow

    Specific volume

    TS=(P)

    TS=(P)

    Enthalpy

    Enthalpy

    Enthalpy

    Enthalpy

    Pressure

    Concentration (Mass)

    Net calorific value

    Mole fraction

    Mole fraction (mole, dry)

    Entropy

    Volume flow

    Specific volume

    No.20/21: In the case of water-/steam pipes this value refers to the boiling temperature, in the case of humid air to the dew temperature.

     

     

    Values for FDAMP

    Limits for the change gradient GRi

    lower limit

    for GRi

    upper limit for GRi

    CHL3

    for Iteration

    Damping behaviour

    <ITCHL3

    >=ITCHL3

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    0.3

    0.3

    0.3

    0.75

    0.2

    0.1

    0.05

    99999.0

    9999.0

    2.0

    1.25

    1.0

    0.6

    0.3

    0.15

    0.15

    0.15

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    Characteristic Lines

    CCHL3 - correction factor for CHL3

    This characteristic makes it possible to change the maximum possible change factor CHL3 continuously during the iteration (ITCHL3 enables an abrupt change in the iteration step ITCHL3). Normally one would be able to make the permissible deviation narrower at the end of iteration, in order to achieve a faster convergence.

    x-value: Iteration step

    y-value: correction factor (used CHL3 = default value CHL3 * y-value)


    Physics Used

    Equations

    Relative change

     

                 (scheduled value+ADD-actual value)  

    Si =     -----------------------------------------------------

                                 Scheduled value                

     

    Definition of the sensitivity

     

                            |     f- f(old)                  |

    CHL3    =       | ------------------------    |

                            |     f(old)                     |

     

    Relative change of the correction value f

     

                            Df       

    Ki=      ------------------------    

                              f                   

     

    During the iteration steps 1 to 10, GRi will be set as follows:

    from iteration 1 to  5: GRi = 0.95, and

    from iteration 6 to 10: GRi = 0.90  .

    The gradient GRi will be calculated after iteration 11 by the interpreting the previous controlling success.

    Change gradient

     

                Ki

    GRi = -----

                Si

     

    The controller has a "self-learning" characteristic i.e. the best possible change of the correction value for the next iteration is taken from the analysis of the controlling success of the last iteration step. For this, the change gradient is used, which is defined as follows: The change gradient is a measure of the relative change of the correction value as a function of the relative deviation. A change gradient of GRi=1.0 results in a relative change of, for instance, 5% to a change of the correction value of this 5% itself. The change gradient set to GRi=0.5 returns, for this change, the correction value of 2.5%.

    The value calculated in the last two steps is used to determine the new correction value in accordance with the following list.

    Correction value

     

    Df = f *  GRi * Si

    f(new)  = f(old) * (1.0 + Df) * FCHAR

     

     


    Component Displays

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    Example

    Click here >> Component 12 Demo << to load an example.

    See Also