levels
In the heating example that I used in the Control tutorial, I showed a diagram that used a thermostat to measure the temperature of a room. At the time, I was interested in showing the heat flow and was not much interested in exactly how the temperature was measured.
But now supposed I need to work with specific part of the system that measures the temperature of the room. Instead of drawing up a whole new diagram, I'll just specify that the thermostat is a sub-system of the main system and make it into a separate diagram.
To show that the thermostat has another diagram associated with it, so I color it red and add a line to link the two.
Notice that the new diagram is a self-contained system model of its own. It has a source and two sinks, a process, two decisions, and various relationships.
Here, I included the sub-system diagram on the same page as the main system. But I could easily have put it on a separate page. Very large systems designs may consist of thousands of such pages ... in which case it is vitally important to label the pages and their links correctly.
In the new diagram I have shown a thermometer/trigger mechanism that sends a signal if the temperature gets above or below the unit's settings. I don't show exactly how the triggers work, but if this was needed I could add yet another sub-system, linked to this one, to show the extra details.
Remember This
A systems diagram may be presented in levels. Each level should be a separate system itself. To guarantee future reference, the sub-system should be carefully named and linked to the main system.
The End
This completes the tutorial on systems diagramming. My goal was to show you some of the basic symbols and demonstrate how they can be used to illustrate various systems behaviors.
Systems designers constantly go back and forth between diagrams of the system's structure and graphs of the system's outputs. They compare these to their observations of the real world situation and continually fine tune the system model.
To study systems in depth you need to be able to do both.
Home - Diagramming Topics - This was the last one.