ITEM TOOLKIT

S 5 Primary Repaired X
Chapter 9 Markov 211
Furthermore, we assume that the system as a whole is unavailable when both the primary and standby components are
failed. While in principle any number of states can be marked as unavailable, here we will limit it.
20. Right-click the state corresponding to the ‘both components failed’ state. A popup menu appears.
21. In the popup menu, select the State Parameters… option. A dialog box opens.
22. In the dialog box, check the ‘Unavailable State’ option, and click OK.
23. Ensure that in the editor pane, the state is indicated as being an unavailable state of the system by a small circle (A)
appearing next to the state.
A
24. Next, we introduce into the model the transitions representing the failures as well as repairs of the components. By
inserting a transition originating in one state and leading to another, we model the possibility of an event-taking place
that would bring the system from one state to another. In our simple model, we will insert eight transitions, as listed in
the following Table.
From To Description Rate
Both Available Primary Failed Failure of primary component 0.001
Both Available Standby Failed Failure of standby component 0.0001
Primary Failed Both Available Repair of primary component 0.5
Primary Failed Both Failed Failure of standby while primary failed 0.001
Standby Failed Both Failed Failure of primary while standby failed 0.001
Both Failed Primary Repaired Repair of primary while standby still failed 0.5
Primary Repaired Both Available Repair of standby 0.5
Primary Repaired Both Failed Repair of primary while standby under repair 0.001
25. In the Markov toolbar, click the Arrow Link Button (B). This button is used to start the creation of new transitions.
B
26. Left click on the Both Available state. A line originating from the state becomes visible as the mouse is moved around
the Markov canvas.
27. Click on the Primary Failed state. An arrow appears between the two states. The arrow’s label indicates a rate of
occurrence R of 0 (C).
28. Right-click on the label. A popup menu appears.