MALFUNCTION OF MEDICAL EQUIPMENT AS A RESULT OF MAINS BORNE INTERFERENCE

Medical equipment has become more intelligent as the manufacturers hav e incorporated the latest microprocessor based technology. Equipment m alfunction can be caused at any time by inherent errors in the control program but it is particularly important that this is designed to cop e with the effects of electrical interference which, in addition, may cause corruption of the software. We have considered interference foun d in the mains supply in the hospital environment. Using a test protoc ol with appropriate interference simulators, a wide range of medical e quipment was removed temporarily from use and its immunity to electric al mains borne interference tested. Battery operated mains rechargeabl e devices were unaffected by mains voltage variations including drop-o uts and sags whereas mains powered devices were affected to varying de grees of severity. In particular, repetitive drop-outs caused loss of power due to fuse blowing in some life support equipment. Impulses aff ected 25% and pulse bursts 50% of the equipment tested with some evide nce that the more recent designs coped better. The EEC Directive on el ectro-medical compatibility compliance may cause the design of equipme nt to be improved but hospitals will have to cope with the above probl ems in their existing equipment for many years to come.