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9
Behaviour description
BEHAVIOUR DESCRIPTION
The behaviour description for a component consists of a part that is executed once during
initialisation and a part that is carried out in every cyclic calculation step. The same
description syntax applies to both parts.
There are two different approaches to the behaviour description for a component:
•
Equation-oriented approach
The equation-oriented approach describes every new status value or output value as
an explicit function of the inputs, parameters and states. It is particularly suitable for
modelling physical contexts. This approach allows you to describe the change in
continuous state variables using common differential equations as well.
•
Instruction-oriented approach
The instruction-oriented approach describes the calculation of new state variables or
outputs in the form of programming instructions that are processed sequentially in the
specified order. This approach is particularly suitable for modelling technical
behaviour.
The two approaches can also be combined in a component type.
9.1
Conversion of the behaviour description to C# code
Regardless of which approach is used to define the behaviour of a component type, it is
ultimately converted into C# code in the simulation project for every component instance.
This conversion takes place automatically and cannot be seen by and is of no significance to
the user.
Not all syntax errors are detected before the code is generated, so the compiler may also
generate error messages. Please note that the information in such error messages relates to
the generated code that differs from the behaviour specified in the component type in terms
of both syntax and breakdown.
9.2
The equation-oriented approach
In the equation-oriented approach, the syntax in which you set out the behaviour of your
component type consists of relationships in the form of equations, rather than instructions.
These equations explicitly describe how a state variable or an output is calculated from other
variables, for example as follows:
Output = Parameter * Input;
Essentially:
•
Every equation contains the equals sign.
•
On the left of the equals sign is the variable that is being determined. On the right of
the equals sign are the variables that are read (explicit form of an equation).
•
At the end of every equation there is a semicolon.
•
Any variable may occur only once on the left of the equals sign, i.e. a variable may
only be determined once.
The following variables may appear on the left of the equals sign:
•
Outputs
Copyright  Siemens AG, 2013
Process Automation
SIMIT 7 – CTE
Page 49