Teknor Industrial Computers PCI-993, Technical Reference Manual

Page: 182 / 204

TEK933 Specifications A-8
The MTBF is estimated using the prediction data from MIL-HDBK-217F, Reliability
Prediction of Electronic Equipment (Dec. 1991).
The TEK933 board is considered functioning in a Ground Fixed environment as
defined in MIL-HDBK-217F. The calculations are performed at 20
°
C with a
temperature rise of 10
°
C which is due to heat dissipated by active components.
It is assumed that only one failure at a time can occur and that the failure of any
component will result in the system becoming inoperative or, as a minimum, resulting
in a degraded mode of operation requiring repair action. All components are considered
as having an exponential distribution of time to failure, with a constant failure rate. A
failure rate is attributed to each component called in the parts list, according to the
stress levels it is submitted during normal operation.
The components with the highest calculated failure rate in the TEK933 reliability
prediction are: the Pentium

CPU, 33
Ω
resistors, the 16 bus drivers (74FCT16245)
and the Cache memory (256KB and 1MB).
The ball-bearing heatsink/fan assembly has been excluded from the reliability
calculations. However, based on manufacturer field data, the heatsink MTBF is equal to
115,000 hours and the mechanical part (fan) does not require any preventive
maintenance.