A Fault Propagation Editor allows you to specify how faults propagate through an eXpress model. More specifically, this editor allows you to specify, for a selected failure mode,
1) which downstream failure modes will look like they have occurred when the selected failure mode occurs and
2) what upstream failure modes will, when they occur, look like the selected failure mode has occurred.
To open the Fault Propagation Editor use the path shown to th right
OR
This command can also be called from the Design Menu "Edit Fault Propagation"
Window Options
When invoked for a single failure mode, the Fault Propagation Editor will appear as follows:
Listed on the left is the selected failure mode. On the right are all failure modes that are associated with downstream functions. If the selected failure mode will never cause one of the downstream failure modes to look like it has occurred, then disable the checkbox beside the downstream failure mode. Here the non-electrical functions have been excluded when the Battery Charge is low.
We highly recommend that you use this dialog only under DSI’s guidance—not because you can mess up your model, but rather because you could waste a lot of time with this dialog making edits that will in no way impact your analysis in eXpress.
eXpress models are based on a combination of two causal models—a functional dependency model and an optional failure mode and effect model (often imported from a FMECA). To add a fault propagation model—a third model that may well require more effort than the other two models combined—is, needless to say, a risky endeavor. Truth be told, we at DSI do not believe that this level of effort should be required across an entire design (let alone for an entire system).
There is, however, one specific situation in which this feature will be very useful—it arises when failure modes are used as test coverage anchors. Experienced Analysts may also find the Fault Propagation Editor useful for identifying errors in the “Affected Functions” settings for various failure modes. At any rate, fault propagation editing should be thought of as a technique to be applied in certain, very specific instances—not as an alternative way of modeling your system.
If you believe that this editor will be useful for your model or system, contact DSI and let us walk you through its use.
