Before and after these environmental


tests took place, optical engineers set up an interferometer, the main device used to measure the shape of the Webb telescope’s mirror. An interferometer gets its name from the process of recording and measuring the ripple patterns that result when different beams of light mix and their waves combine or “interfere.” Waves of visible light are less than a nanometre long, and optics on the Webb telescope need to be shaped and aligned even more accurately than that to work correctly. Making measurements of the mirror shape and position by lasers prevents physical contact and damage (scratches to the mirror). So, scientists use wavelengths of light to make tiny measurements. By measuring light reflected off the optics using an interferometer, they are able to measure extremely small changes in shape or position that may occur after exposing the mirror to a simulated launch or temperatures that simulate the sub- freezing environment of space. During a test conducted by a team


from Goddard, Ball Aerospace of Boulder, Colorado, and the Space Telescope Science Institute in Baltimore, temperature and humidity conditions in the cleanroom were kept incredibly stable to minimise fluctuations in the sensitive optical measurements over time. Even so, tiny vibrations are ever- present in the cleanroom that cause jitter during measurements, so the interferometer is a “high-speed” one, taking 5000 frames per second, which is a faster rate than the background vibrations themselves. This allows engineers to subtract out jitter and get good, clean results on any changes to the mirror’s shape.


“Some people thought it would not be possible to measure beryllium mirrors of this size and complexity in a cleanroom to these levels, but the team was incredibly ingenious in how they performed these measurements and the results give us great confidence we have a fantastic primary mirror,” says Lee Feinberg, Webb’s telescope optical element manager. The Webb telescope will be shipped to


Johnson for end-to-end optical testing in a vacuum at extremely cold operating temperatures. Then it will continue on its journey to Northrop Grumman Aerospace Systems in Redondo Beach, California, for final assembly and testing prior to launch in 2018. EE


ENGINEERS GAIN CERTIFICATION IN VIBRATION ANALYSIS


Two engineers from global automotive and industrial supplier Schaeffler have gained vibration analysis qualifications from certification body Mobius Institute.


Ian Pledger, Service Engineer at Schaeffler (UK) Limited gained Vibration


Analyst: Category III certification according to ISO 18436-2: 2014. Category III is the third in a four-category classification programme for this qualification. David Goves, Applications Engineer at Schaeffler (UK) Limited, received Vibration Analyst: Category II certification. ISO 18436-2:2014 is an international standard that specifies requirements


for the training, relevant experience and examination of personnel performing condition monitoring and diagnostics of machines using vibration analysis. The certification provides recognition and evidence that the holder is able to perform vibration measurements and analysis for machinery diagnostics using a range of vibration measurement equipment. The course syllabus for ISO 18436-2:2014 Vibration Analyst training involves


the study of the principles of vibration, data acquisition, signal processing, condition monitoring, fault analysis, corrective action, equipment knowledge, acceptance testing, equipment testing & diagnostics, reference standards, reporting & documentation, fault severity determination, rotor/bearing dynamics, and a training examination. Pledger comments: “In February 2017, I attended a five-day training course at the Schaeffler Training Centre in Eltmann, Germany, along with 11 other Schaeffler engineers from around the world. The course involved four days of intensive instruction followed by a four-hour examination on the final day. This certificate is important as customers can rest assured that any vibration analysis provided by Schaeffler in the UK is carried out by a competent, experienced engineer that holds a globally recognised qualification in this subject.” Goves states: “The range of services that Schaeffler UK now offers includes


condition monitoring using both online and patrol monitoring, vibration analysis and bearing failure analysis, as well as training and consultancy. Earlier this year, I attended a five-day training course at RMS (Reliability Maintenance Solutions), a certified Mobius Institute training provider based in Colchester.” Outside the UK, Schaeffler provides its own training courses accredited to


DIN ISO 18436-2. All vibration experts trained by Schaeffler have passed their certification examination. Instructors in Schaeffler’s training programme have many years of professional experience in machine monitoring, are certified to ISO 18436-2 Category III and have had additional training as an instructor. Schaeffler is continuously expanding its training network according to the same quality standards.


Climatic & Vibration Testing 2017 /// 3


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