Tests in product development

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  • 1. Tests in Product Development - Cases of Medical DevicesRaimo Sepponen, prof. Aalto UniversityElectronics Department
  • 2. Tests in Medical Device development• Tests required by Medical Device Directive• Tests by the quality control and international standards• How to test functional safety?• Special but important problem area: Electomagnetic Compatiblity (EMC)
  • 3. Mechanical Failure: Falling head of a radiation therapy unitThese devices are not related to the case – shown only for demonstration!!
  • 4. Electromechanical Failure: Unexpected movement of C-arc of mammography device These devices are not related to the case – shown only for demonstration!!Reason: Opening of electromechanical brakes during drop of mains voltage
  • 5. Increasing risks of poor EMC FDA + Evaluation Engineer
  • 6. Evaluation Engineer
  • 7. Rapidly changing electromagnetic environment – basis of standards are old already when the are published FDA
  • 8. Wireless communication is a major noise source FDA
  • 9. Failing Apnea Alarm Apnea alarm with poor RF filtering detects modulated field and assumes FM Transmitter that baby is breathing Field modulated by movements coupled to sensor matMother moving in kitchen
  • 10. Walkie-talkies and cellphones interfere with medical equipmentMany types of hospital equipment are susceptible to RF radiation from hand-portable mobile radio transmitters – diagnostic equipment such as ECGs, EEGs,pulse oximeters and other physiological monitoring equipment; and therapeuticequipment such as infusion pumps, ventilators and defibrillators. Physiologicalmonitoring equipment is very sensitive – hence very susceptible.Example: The type of modulation employed by the mobile transmitter can besignificant. For example, an external pacemaker withstood a GSM signal(modulated at 217Hz) at 30V/m field strength, but TETRA modulation (17Hz)caused interference at 3V/m. www.emcuk.co.uk
  • 11. Fibreglass ambulance roof causes death of patientMedical technicians taking a heart-attack victim to the hospital in 1992 attached her to amonitor/defibrillator. Unfortunately, the heart machine shut down every time thetechnicians turned on their radio transmitter to ask for advice, and as a result the womandied.Analysis showed that the monitor unit had been exposed to exceptionally high fieldsbecause the ambulance roof had been changed from metal to fibreglass (to let in moredaylight) and also fitted with a long-range radio antenna. The reduced shielding from thevehicle roof combined with the strong radiated signal proved to be too much for themonitor/defibrillator.Ambulances in the U.K. are typically fitted with radio transmitters with 100W oftransmitted power (ERP), and the resulting field strengths near the roof, where themedical equipment is often installed, can exceed 70V/m in a vehicle with a metal roof.Compare this with the 3V/m and 10V/m RF field susceptibility tests required by themedical devices safety standard EN 60601-1-2. Equipment for fitting in ambulances andsimilar environments must be able to function correctly despite such strong RF fields, sothey need to have greater immunity www.emcuk.co.uk
  • 12. Static Elecricity• Example: A fluid dispenser often malfunctioned when nursing staff entered the room• Reason: Static electric discharges in clothing due to interactions of clothes and items in pockets
  • 13. Static discharges generated by metal/dielectric contacts – Electric field D.C.Smith: EOS/ESD Symposium 99-329
  • 14. Coins in plastic bag – Magnetic field D.C.Smith: EOS/ESD Symposium 99-329
  • 15. Hazards due to user errors• Example: Magnetic Resonance Imaging – burn injury
  • 16. Burn injuries during MRI L R loop loop U C Cair skin Cskin R skin R skinRadiology 1996; 200:572-575
  • 17. Testing for Functional Safety• Know the environment where the product is used• The environment is changing continuously• Collect user experiences – not only from your own products• Try to develop non-standard tests which reveals the unexpected malfunctions
  • 18. Message Tests according to standards do not ensure functional safety