Abstract

Chris and Fred discuss what happens when you can’t avoid having the MTBF imposed upon you – even if it is your own organization and not the customer. Perhaps you are told that ‘our competitors quote the MTBF … so we have to as well!’ But you can (sneakily) tailor test data to get whatever MTBF you want. You can make life easy on yourself by not challenging this paradigm (noting that you will most likely get an unhappy customer). But it is almost impossible to apportion MTBF goals to individual designers that even allow the motivated ones to create a reliable system. So what do you do? Listen to this podcast to help you on your reliability journey.

Key Points

Join Chris and Fred as they discuss what you, as a reliability engineer, need to do when you are forced to be measured in terms of the MTBF and nothing else. The MTBF is usually imposed when the customer asks for it, or your organization is trying to conform with industry norms. But the problem with the MTBF is that it usually doesn’t practically mean anything for the customer … and it is difficult to assign accountability to designers.

Among other things, the MTBF (which is based on an assumption of the constant hazard rate) can’t incorporate any understanding of things that wear-in versus wear-out.

Topics include:

• Educating your boss (or your marketing team) to unveil the horrors of the MTBF. Simply demonstrating in a simple way that the MTBF is going be the point by which anywhere between 50 and 100 per cent of systems will have failed can be very enlightening.
• Educating the customer if they are simply asking for the MTBF. Customer relationships are a two way street. Engaging an ill-informed customer shows you care, and it also shows that you understand what they actually want. You can also use this conversation to demonstrate that competitors aren’t as advanced as you are if they insist on staying with the MTBF.
• … noting that most military customers are fixated on the MTBF. ‘MIL-HDBKs’ were written before we all had Microsoft Excel, meaning that the reliability tests they described had to be simple (… as in based on the MTBF). But these ‘MIL-HDBKs’ have been withdrawn and we (should) have moved on. So why do we keep using them?
• Generate a reliability requirement. If you have an idea of operational life, you should be able to convert an MTBF into a system level reliability goal.
• Don’t apportion MTBF. This doesn’t work.
• … but apportioning reliability does. This allows designers to focus on specific reliability characteristics. Which means that you allow them to be successful, and make your customers happy.

Enjoy an episode of Speaking of Reliability. Where you can join friends as they discuss reliability topics. Join us as we discuss topics ranging from design for reliability techniques, to field data analysis approaches.

SOR 422 What Do I Do When the MTBF is Imposed on Me?Christopher Jackson

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