SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Tom Clark
Date posted: Thu Jul 11 14:46:20 US/Eastern 2002
Subject: RAC FIT Rates
We have received some test reports from a DC-DC converter vendor. They show an MTBF of 3547773 hours with a total failure rate for the assembly of .281867 The reports are labeled with PRISM v1.3 and RAC. The standard for FIT rate is failures in 10^9 hours, however the failure rate here only makes sense if it is out of 10^6 hours. Does RAC do things differently, or is there some other explanation for this dioscrepancy?
Subject: PRISM failure rate
Reply Posted by: B.W.Dudley
Date Posted: Thu Jul 11 14:11:18 US/Eastern 2002
All the RAC databases are in failures per million hours or million miles. You are correct in that FIT stands for failures per billion hours. If the FIT term is used with PRISM, one needs to change the DC/DC converter to 281.887 failures per billion hours.
Incidentally, failure per million hours has been in use for decades and all MIL-HDBK-217 data are in failures per million hours. This is the standard that we built the PRISM from, so the use of failures per million hours is the level that we have continued.