The 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.
The fault propagation controls in eXpress provides the Analyst with the capability to isolate unlike faults away from each other. For example many times when working with fluid systems the pressure, flow and the temperature of the system are propagating through the system together as separate functions. By defining an anchor on a failure mode that tests either the Temperature, flow or Pressure failures you can use the fault propagation capability to isolate the desired failure modes away from the other failure modes. By doing this you are not losing any capability of testing either pressure, flow or temperature but rather you are breaking the testing into smaller segments to improve visibility for the diagnostic Isolation, FMECA and Fault trees.
The Fault Propagation Editor will appear as shown to the right:Listed on the left is the selected failure mode. On the right are all failure modes that are associated with the downstream or upstream functions as selected in the window shown below. If the selected failure mode will never cause one of the downstream or upstream failure modes to look like it has occurred, then disable the checkbox beside the downstream failure mode.
Here we see the Downstream Failure modes turned off that apply to Flow or Pressure. The Temperature Failure modes remain with the testing unit (ECM)
When a test has an anchor, choosing the anchor and using the right hand mouse button as shown to the right will open the Fault Propagation editor shown above so the Analyst can edit the propagation of failure modes to change the failure mode coverage shown in the tests.
The Fault Propagation editor can also be opened from the main toolbar "Design/Failure modes" Menu. to open the window this way the desired failure mode of the object should be selected.
There is 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.
