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Signal flow is the movement of numbers between system components. These numbers might reflect physical quantities or not. In this example, they do not ...
Signals flowing in and out of components are modeled by ports typed by interface blocks that have flow properties typed by numbers.
In this example, ports are typed by RealSignalOutElement and RealSignalInElement from the signal flow library ... which both have a flow property rSig typed by Real, from SysML, as shown in Figure 49.
This value type has no unit, reflecting that the signals are not measurements of physical quantities and do not follow conservation laws.
The amplifier, filters (high-pass and low-pass), signal source, and signal sink have properties g, alpha and xi, amp, and scope, respectively.
The amp, alpha and g properties have the PhSConstant stereotype applied, specifying that their values are constant during each simulation run.
The xi and scope properties have the PhSVariable stereotype applied, specifying that their values might vary during simulation.
Equations define mathematical relationships between the values of numeric variables. Equations in SysML, are constraints in constraint blocks that use properties of the blocks (parameters) as variables.
In this example, a constraint block BinarySignalComponentConstraint defines the parameters for one input (ip) and one output (op), common to amplifiers, low-pass filters, and high-pass filters, as shown in Figure 51.
The amplifier, low-pass fil[t]er, and high-pass filter constraints show the input-output relationship of these components as the signal passes through them.
The amplifier changes the signal strength by a factor gain, the low-pass filter eliminates the high-frequency components of the incoming signal, and the high-pass filter eliminates the low-frequency components of the signal.
The mixer constraint specifies the relationship between its one output and the two inputs that come from the low-pass and high-pass filters. The constraint defines the output to be the average of the inputs.
The source constraint specifies a sine wave signal with the parameter amp as its amplitude. The sink constraint displays (scopes) the output signal from the signal processor.
Equations in constraint blocks are applied to components using binding connectors in component parametric diagrams.
Component parametric diagrams show properties typed by constraint blocks (constraint properties), as well as component and port simulation variables and constants.
Binding connectors link constraint parameters to simulation variables and constants, indicating their values must be the same.