Hi all,

We would like to impliment MTBF & MTTR statistical figures, are there any standards or guidelines on this issue ?

Thanks in advance

Ronny

 

Ronny,

The most widely known and used reliability prediction is MIL-HDBK-217 Handbook and Bellcore TR-332.
Check http://www.t-cubed.com frequently asked question section.

 

Dear Ronny:
(1) MILITARY HANDBOOK 217F is the latest version, but the last time I looked the Department of Defense was NOT going to update the models for components in MIL-HDBK-217F. This means that predictions for MTBF will be growing more and more conservative and out of date as more and more new technology is produced. This is all for predictions which means counting each component
and adding up the failure rate for each component and summing all contributions for the overall module. A system is the sum of all the
modules.

(2) BELLCORE TR-332: is really directed at the telephone industry, not the process control industry. MTBF Predictions per BELLCORE will therefore be conservative when applied in process control.

(3) MTTR:depends more heavily on the end-users' policies. Many systems today have system monitoring capabilities, which announce failures (or conditions) and identify the item that needs to be addressed. The total MTTR, Mean Time To Repair, is therefore very small. The big time consuming items become the spares policy and the training policy of the end-user.
Spares on site? Personnel well trained? Then MTTR is Minimized.

(4) IEC 300: "Dependability Standard". Many companies will track their equipment in the field in order to meet the requirements of IEC 300. They will then be able to give you actual, real-life field numbers for MTBF. My old company, The Foxboro Company, did this until they laid me off in October 2000. Now, there are no longer any reliability engineers at The Foxboro Company (the European reliability engineer retired in May 2000), and the MTBF data will get stale rapidly, as time goes by.

So, if you want predictions for relative reasons, 217F may suffice. If you need actual field numbers, for IEC 61508 analyses, as an example,
then go directly to the company.
MTTR: determine by your policies.
If you would like to discuss further, feel free to contact me:
[email protected]
Sincerely,
John Peter Rooney
ASQ Certified Reliability Engineer #2425.

 

I had a Belcore program that had ESS as well as Burn-in as a multiplier to estimate improvements in the infant mortality of a box. Now looking at my belcore spec (issue 6, dec 1997) ESS is not mentioned.? Do I have an old spec? or what?