This post is by Stuart Brown, Environmental Managing Director at TRaC.
Many people see reliability testing as a black art. Engineers create a test setup that replicates the stresses of years of normal use in a matter of hours - how can they know their testing correlates with use in the real world?
The two key elements of effective reliability testing are HALT and HASS. Understanding these methods is invaluable for any engineer developing reliable products (which hopefully is everyone who reads this post!) as is appreciating why traditional ESS techniques are often unable to meet today's demanding reliability requirements.
HALT (Highly Accelerated Life Test)
Many people see reliability testing as a black art. Engineers create a test setup that replicates the stresses of years of normal use in a matter of hours - how can they know their testing correlates with use in the real world?
The two key elements of effective reliability testing are HALT and HASS. Understanding these methods is invaluable for any engineer developing reliable products (which hopefully is everyone who reads this post!) as is appreciating why traditional ESS techniques are often unable to meet today's demanding reliability requirements.
HALT (Highly Accelerated Life Test)
HALT is a process applied during the development phase of a new product, to validate design robustness and is most commonly used to identify potential weaknesses in electrical and electronic assemblies.
Modifications can then be made so that volume manufacturing can begin with a mature product design, thus minimizing costly warranty issues and potentially disastrous product recalls.
The fundamental principle is to apply stepped applications of increasingly powerful environmental stresses until latent (i.e. hidden) defects are exposed. The most commonly applied stresses (but not exclusively) are thermal and broadband multi-axis random vibration. These are used individually and then in combination.
If a product has an intrinsic weakness, exposure to day-to-day operating conditions will eventually cause it to fail at that point of weakness. By careful application of increased stress levels in HALT, the time for that same failure to occur is dramatically reduced.
A benefit of HALT is that very few product samples are needed and the process can be completed very quickly. There is no Industry Standard for HALT but the following stresses are usually applied to one or more functionally monitored test specimens until they cease to function:
• Progressive reduction in temperature to determine the lower operational limit and then the lower destruct limit
• Progressive increase in temperature to determine the upper operational limit and then the upper destruct limit
• Progressively more stressful thermal cycling at high, linear, rates of change of temperature
• Broadband random vibration at increasing intensity levels
• A combination of thermal and random vibration stresses
At each stage when a failure occurs, root cause analysis is performed, corrective action is implemented and the process continues until the fundamental limit of the product technology is reached.
Part 2 will follow next Wednesday
Previous Certification & Test entries:
* Certification & Test: Flammable atmospheres - A change to the ATEX Standards for zone 2 equipment
* Certification & Test: How to make sure products comply with Noise at Work regulations
* Certification & Test: The impact of the Noise at Work Directive on your designs
* Certification & Test: How am I going to test that?
* Certification & Test: Electrical safety is still important!
* Certification & Test: Why bother with vibration testing?
* Certification & Test: Do I really need earthquake testing?
* Certification & Test: Differences between earthquake and vibration testing?
* Certification & Test: Safety - it's a complex business!
* Certification & Test: What's the point of a Notified Body?
* Certification & Test: The difference between Bluetooth and ZigBee testing?
* Certification & Test: Is above 1GHz the new Wild West?
* Certification & Test: Where have all the ZigBee products come from?
Modifications can then be made so that volume manufacturing can begin with a mature product design, thus minimizing costly warranty issues and potentially disastrous product recalls.
The fundamental principle is to apply stepped applications of increasingly powerful environmental stresses until latent (i.e. hidden) defects are exposed. The most commonly applied stresses (but not exclusively) are thermal and broadband multi-axis random vibration. These are used individually and then in combination.
If a product has an intrinsic weakness, exposure to day-to-day operating conditions will eventually cause it to fail at that point of weakness. By careful application of increased stress levels in HALT, the time for that same failure to occur is dramatically reduced.
A benefit of HALT is that very few product samples are needed and the process can be completed very quickly. There is no Industry Standard for HALT but the following stresses are usually applied to one or more functionally monitored test specimens until they cease to function:
• Progressive reduction in temperature to determine the lower operational limit and then the lower destruct limit
• Progressive increase in temperature to determine the upper operational limit and then the upper destruct limit
• Progressively more stressful thermal cycling at high, linear, rates of change of temperature
• Broadband random vibration at increasing intensity levels
• A combination of thermal and random vibration stresses
At each stage when a failure occurs, root cause analysis is performed, corrective action is implemented and the process continues until the fundamental limit of the product technology is reached.
Part 2 will follow next Wednesday
Previous Certification & Test entries:
* Certification & Test: Flammable atmospheres - A change to the ATEX Standards for zone 2 equipment
* Certification & Test: How to make sure products comply with Noise at Work regulations
* Certification & Test: The impact of the Noise at Work Directive on your designs
* Certification & Test: How am I going to test that?
* Certification & Test: Electrical safety is still important!
* Certification & Test: Why bother with vibration testing?
* Certification & Test: Do I really need earthquake testing?
* Certification & Test: Differences between earthquake and vibration testing?
* Certification & Test: Safety - it's a complex business!
* Certification & Test: What's the point of a Notified Body?
* Certification & Test: The difference between Bluetooth and ZigBee testing?
* Certification & Test: Is above 1GHz the new Wild West?
* Certification & Test: Where have all the ZigBee products come from?
After obtaining his Bachelor's degree in engineering, Jonathan worked for a number of engineering companies prior to obtaining a teaching role at the University of Hull (England). In 1995 he joined KTL, an internationally renowned test laboratory which then became TRaC, as part of the Digital Group specialising in regulatory requirements for digital telecommunications equipment. During his time at the company he has, among other things, been appointed as Senior Protocol Engineer, and Approvals and Homologation Group Manager. Jonathan has actively participated in various technical working groups for the ZigBee Allianceâ and is currently the ZigBee Qualification Group (ZQG) Lead Technical Editor. 
Steve is Managing Director for the EMC and Safety business of TRaC and has been involved in EMC and product approvals for 19 years. In addition to the day to day running of the business, Steve is actively involved in EMC standardisation both in commercial and defence areas. In addition to being the UK Principal expert on EMC standardisation of Industrial, Scientific and Medical (ISM) products he is also the convenor of CISPR/B/WG1 who has the responsibility of writing the International standard, CISPR 11. Steve wrote the CE marking annex to the UK's defence EMC standard as well as being co-convenor of CENELEC TC210/WG9, responsible for writing a guide on approval of military systems with commercial (CE Marking) requirements.
Joe Lomako MSc is the Business Development Manager of Telecoms and Radio at TRaC. He has been involved in the testing and compliance industry for over 15 years. Prior to joining TRaC Joe specialised in EMC, EMF Exposure and Radio compliance.
Appointed Test Manager in 2007, following three years as Projects Manager at TRaC, having previously worked as Head of Environmental Testing at another UKAS accredited test house. Over 20 years' experience of modelling, testing and measurement in the structural dynamics and seismic fields.
Chris has worked in electrical safety compliance for over 17 years. Having previously worked for BSI, he joined TRaC in 1996, progressing through a number of testing roles before becoming Safety Product Manager in 2006.
Appointed Commercial Manager - Analysis in November 2009. Prior to joining TRaC, he was the Business Development Manager at Onward Technologies, an engineering services company based in India. Graham has spent over 20 years working in the CAD / CAE domain selling both engineering services and engineering systems. 
Stephen Tait joined KTL, an internationally renowned test laboratory which then became TRaC, as part of the Telecom Group specialising in telecommunications product testing for worldwide approvals. Stephen is also responsible for the Telecoms commercial activities within the TRaC group.
Simon Barrowcliff is the Director of the ATEX Notified Body at TRaC. He set up TRaC's Lancashire-based, ATEX business in 2002 and has been heavily involved in EX testing and compliance since then. Simon also runs TRaC's certification schemes for electrical safety under the IECEE CB scheme. He is a chartered electrical engineer with more than 20 years experience of product compliance for electrical and mechanical equipment.
Appointed Managing Director in November 2007. Previously he was Test Facilities Manager for Flight Refuelling, part of the Cobham group, and spent his early career in the Environmental Engineering Department of British Aerospace at Stevenage.
Brendan was appointed Sales Director in August 2009. He joined the group in 2005 as Business Development Manager for environmental test services. Before joining TRaC he spent five years in Application Engineering and Technical Sales roles for automotive test equipment. He studied Mechanical and Manufacturing Engineering at Trinity College Dublin.
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