Additional analysis of the use cases defines the structural
and behavioral composition of the control system. The two essential
systems are specified as SysML blocks–a ControlSystem block and a
SystemUnderControl block. Use an internal block diagram to create
the structural design.
The ControlSystem block and SystemUnderControl blocks form
the system context and are defined in the starting point External
Flows internal block diagram. The ControlSystem and SystemUnderControl
blocks, represented as parts (cs and s), are coupled together in a
closed loop control system.
Locating the External
Flow internal block diagramIn the browser, expand and double-click External Flows to
open the diagram.
You use this diagram to specify the connections between the
SystemUnderControl and the ControlSystem blocks and the flow of heat
and temperature between these two systems. SysML requires that such
connections be specified between block instances within a context,
so you can use the Context block to define the context and the parts
are the instances of the SystemUnderControl and the ControlSystem
blocks.
The starting point External Flows diagram has the input
side connection (heat) specified, but the connection for the output
side (temperature) is missing.
Connecting
blocks through flowports
To complete the closed loop
design in the External Flows internal block diagram:
The flow attribute name, output, and its type, degC are
displayed next to the flow arrow on the diagram.
Analyzing
behavior in an activity diagramTo open the starting
point activity diagram:
- In the browser, open the FunctionalAnalysisPkg.
- Double-click the OperateSystem activity. This opens the activity
diagram for the activity.
This activity begins by waiting for an evPower event.
Upon receipt of the event, flow of control splits concurrently along
two paths:
- a1, where the behavior alternates between two modes when it receives
the evMode event: normal, where heating is enabled, and standby, where
heating is disabled.
- a2, where the system attempts to maintain the temperature (the
temperature is not maintained while heating is disabled)
The interruptibleRegion defines the subset of behavior that can
be interrupted to power off the system, terminating the activity.
Adding
an action pin and parameter
To add a temperature
action pin and the associated parameter:
- Select the Action Pin tool
. Add an action pin to the Maintain temperature
action.
- Use the Features window for the new action pin to set its name
to "temperature," its type to degC selected from the valueTypes in
the TypesPkg, and its direction to In.
- Select the Activity Parameter tool
. Add an activity parameter to the activity
by adding it to the right side of the diagram frame near the heat
parameter.
- In the Features window for the new activity parameter, type temperature as
the name, select degC for type from the TypesPkg,
and set the direction to In. Click OK.
- In the diagram, expand the parameter symbol to fit around the
name.
- Select the ObjectFlow tool
and connect the temperature activity parameter
to the temperature action pin.
Your activity diagram should resemble this example.