This post is by Chris Stone, Environmental Test Manager at TRaC.
What's the difference between earthquake and vibration testing?
When Engineers are told that their design will have to withstand seismic events and are faced with designing for and carrying out earthquake testing (see my previous post about how this is increasing), it is often their first experience of this test regime and at first glance, the complicated test specifications are a real cause for concern!
Most Engineers have some experience of vibration testing and understand acceleration levels and the frequency of vibration but Earthquake testing is commonly specified by Required Response Spectra (RRS) as the tests are typically simulating events that are over in 30 seconds but involve large displacements at low frequency.
What's the difference between earthquake and vibration testing?
When Engineers are told that their design will have to withstand seismic events and are faced with designing for and carrying out earthquake testing (see my previous post about how this is increasing), it is often their first experience of this test regime and at first glance, the complicated test specifications are a real cause for concern!
Most Engineers have some experience of vibration testing and understand acceleration levels and the frequency of vibration but Earthquake testing is commonly specified by Required Response Spectra (RRS) as the tests are typically simulating events that are over in 30 seconds but involve large displacements at low frequency.
I'm often asked how seismic testing differs from vibration testing - the main differences are:
Previous Certification & Test entries:
* 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?
- Earthquake testing is typically carried out from 0.1 to just 70Hz (although our table can reach 100Hz)
- Earthquake tests generally involve excitation in all three axes simultaneously, whereas with vibration testing the sinusoidal or random vibration is carried out in axis and then the equipment under test is remounted to test the other two axes in turn.
- Earthquake testing may comprise 6 degrees of freedom, with roll, pitch and yaw as well as the three translational axes of shaking. Vibration testing has just one linear degree of freedom.
- Earthquake testing involves excitation with a much bigger displacement (up to 300mm peak to peak). Vibration testing, using electrodynamic shakers, is typically limited to 50mm peak to peak.
- Earthquake testing is carried out to give confidence that equipment can survive and operate when subjected to a thirty second shake that may only statistically occur once in ten thousand years. Vibration testing is carried out at accelerated levels to simulate a lifetime of exposure to vibration in a much shorter timescale.
- To achieve the different characteristics, earthquake testing uses hydraulic actuation whereas shakers are typically electromagnetic devices.
- Usually earthquake testing requires the equipment to be functional during testing and may be repeated to account for different operational states e.g. all relays, switches, etc are left open, the system is tested to make sure that it will continue to operate correctly, then the process is repeated with the electromechanical parts in the opposite state.
Previous Certification & Test entries:
* 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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