ISO/TR TECHNICAL REPORT 24119 Firstedition 2015-11-15 Safety of machinery Evaluation of fault masking serial connection of interlocking devices associated with guards with potential free contacts Sécurité des machines-Evaluation du masquage de fautes dans les connexions en seriedes dispositifs d'interverrouillage associés aux contacts sans potentiel Referencenumber IS0/TR24119:2015(E) LSO @IS02015 IS0/TR24119:2015(E) COPYRIGHTPROTECTEDDOCUMENT @ IS0 2015,Published in Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISo's member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8. CP 401 CH-1214 Vernier, Geneva, Switzerland Tel.+41227490111 Fax+41227490947 copyright@iso.org www.iso.org @ IS0 2015 - All rights reserved IS0/TR24119:2015(E) Contents Page Foreword .iv 1 Scope .1 2 Normative references .1 3 Termsand definitions .1 4 Fault masking. .5 4.1 General .5 4.2 Direct fault masking 6 4.3 Unintended reset of thefault .6 4.4 Cablefault withunintended reset 5 MethodologyforevaluationofDCforseriesconnected interlockingdevices .8 6 LimitationofDcbyeffectsofseriesconnecteddevices .9 6.1 General .9 6.2 Simplified method for the determination of the maximum achievable DC .9 6.3 RegularmethodforthedeterminationofthemaximumachievableDC .9 Estimation of the fault masking probability 9 6.3.2 DeterminationofthemaximumachievableDC 10 6.4 Interlockingdevices with potentialfreecontacts and otherpotentialfree contacts of deviceswithdifferentfunctionalityconnected in series .12 7 Avoidingfaultmasking .13 Annex A (informative) Examples of the application of the evaluation methods described in 6.2 and 6.3 .14 Bibliography 20 isn a adardzan rights reserved ii