Displaying Mtbf Information; Table 2-2. Example Mtbf Calculation - NEC Express5800/320Ma Technical Reference Manual

MTBF Calculation
The calculation of the new the MTBF is as follows:
MTBF =
For the MTBF to be below the threshold, the FailureCount must be equal to or greater
than 3, and the calculated the MTBF must be below the threshold. For example,
Table 2-2 shows the progression of failures causing recalculation of the MTBF. The
MTBF threshold in this example is 600, so the device is removed from service when
the new MTBF is less than 600, or 517 in the example.

Table 2-2. Example MTBF Calculation

Current MTBF
1000
833
700
600

Displaying MTBF Information

To display the current MTBF information for a device in the details pane, you can select
the device in the console tree of ftSMC. The following example shows the time of the
last fault, the MTBF Threshold, the number of faults, and the current MTBF value.
MTBF: Type
MTBF: TimeOfLastFault
MTBF: Threshold
MTBF: NumberOfFaults
MTBF: Current
An out-of-service hardware device remains out of service until you clear the MTBF or
change the MTBF threshold. Inserting a new device clears the MTBF.
A value of 0 (Unknown) for MTBF: Current indicates that the device has not failed
enough times to be able to calculate the MTBF.
CurrentMtbf * (FailureCount - 1) + TimeSinceLastFailure
Failure Count
3
4
5
6
FailureCount
Time Since Last Failure
500
300
200
100
Use Threshold
May 30, 2004 15:07:24
300 seconds
2
532220 seconds
Express5800/320Ma System Features
Managing MTBF Statistics
New MTBF
833
700
600
517
2-5