Mtbf Calculation And Effects - NEC Express5800/320Ma Technical Reference Manual

Managing MTBF Statistics
device to test itself. If the device fails the test, the error is a hard error and the device
is taken out of service. If the device passes the test, the error is a soft error.
The system takes the device out of service and places it in the Broken state under
these circumstances:
•
The error is a hard error.
•
The error is a soft error, and the MTBF is less than the MTBF threshold for the
device.
If the error is a hard error and the MTBF is greater than the MTBF threshold, the system
attempts to enable the device and return it to service.

MTBF Calculation and Effects

The system does not calculate the MTBF until the total error count equals a minimum
number, and then it uses the recorded times of the last minimum number of errors to
calculate the MTBF. If the MTBF has not yet been calculated, the system considers the
MTBF value unreliable and acts as if the MTBF is greater than the threshold.
For each error that occurs, the system performs certain calculations. For each hard
error, the system records the time of the error and increments the total error count.
Then the system takes the device out of service and places it in the Broken state.
Finally, the system calculates the MTBF and compares it with the threshold. One of two
actions occurs:
•
If the MTBF is less than the threshold, the system leaves the device in the Broken
state.
•
If the MTBF is equal to or greater than the threshold, the system attempts to enable
the device and return it to the DeviceReady state.
2-4 Express5800/320Ma: Technical Reference Guide