Machinery Safety 101

Using Form C relays in safety circuits

I recently had a dis­cus­sion with a col­league wanted to know if it was ok for a design to include a form C relay in an e‑stop cir­cuit. You might recall that e‑stop func­tions are required to meet at least PLc/SIL1 require­ments [1], [2]. It’s import­ant to remem­ber that PLc/SIL1 can be met using Cat­egory 1, 2, or 3 archi­tec­tures. See…

Safe Drive Control including Safe Torque Off (STO)

Graph illustrating STO Function
This entry is part 12 of 16 in the series Emer­gency Stop

Ed. Note: This art­icle was revised 25-Jul-17 to include inform­a­tion on safe stand­still. Safe Drive Con­trol includ­ing STO Motor drives are every­where. From DC vari­able speed drives and index­ing drives, through AC Vari­able Fre­quency drives, servo drives and step­per motor drives, the cap­ab­il­it­ies and the flex­ib­il­ity of these elec­tron­ic sys­tems has giv­en machine design­ers unpre­ced­en­ted…

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How to do a 13849 – 1 analysis: Complete Reference List

This entry is part 8 of 9 in the series How to do a 13849 – 1 ana­lys­is

Post updated 2019-07-24. Ed. As prom­ised in pre­vi­ous posts, here is the com­plete ref­er­ence list for the series “How to do a 13849 – 1 ana­lys­is”! If you have any addi­tion­al resources you think read­ers would find help­ful, please add them in the com­ments. Copy­right secured by Digi­prove © 2017 – 2018Acknow­ledge­ments: As cited.Some Rights ReservedOri­gin­al con­tent here is pub­lished under these license terms: X License Type:Non-com­mer­cial, Attri­bu­tion,…

ISO 13849 – 1 Analysis — Part 8: Fault Exclusion

This entry is part 9 of 9 in the series How to do a 13849 – 1 ana­lys­is

Post updated 2019-07-24. Ed. Fault Con­sid­er­a­tion & Fault Exclu­sion ISO 13849 – 1, Chapter 7 [1, 7] dis­cusses the need for fault con­sid­er­a­tion and fault exclu­sion. Fault con­sid­er­a­tion is the pro­cess of examin­ing the com­pon­ents and sub-sys­tems used in the safety-related part of the con­trol sys­tem (SRP/CS) and mak­ing a list of all the faults that could occur in each…

ISO 13849 – 1 Analysis — Part 7: Safety-Related Software

General architecture model of software
This entry is part 7 of 9 in the series How to do a 13849 – 1 ana­lys­is

Post updated 2019-07-24. Ed. Safety-Related Soft­ware Up to this point, I have been dis­cuss­ing the basic pro­cesses used for the design of safety-related parts of con­trol sys­tems. The under­ly­ing assump­tion is that these tech­niques apply to the design of hard­ware used for safety pur­poses. The remain­ing ques­tion focuses on the design and devel­op­ment of safety-related soft­ware…

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ISO 13849 – 1 Analysis — Part 3: Architectural Category Selection

This entry is part 3 of 9 in the series How to do a 13849 – 1 ana­lys­is

Post updated 2019-07-24. Ed. At this point, you have com­pleted the risk assess­ment, assigned required Per­form­ance Levels to each safety func­tion, and developed the Safety Require­ment Spe­cific­a­tion for each safety func­tion. Next, you need to con­sider three aspects of the sys­tem design: Archi­tec­tur­al Cat­egory, Chan­nel Mean Time to Dan­ger­ous Fail­ure (MTTFD), and Dia­gnost­ic Cov­er­age (DCavg). In…

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ISO 13849 – 1 Analysis — Part 2: Safety Requirement Specification

This entry is part 2 of 9 in the series How to do a 13849 – 1 ana­lys­is

This art­icle was updated 2019-07-24. Ed. Devel­op­ing the Safety Require­ment Spe­cific­a­tion The Safety Require­ment Spe­cific­a­tion sounds pretty heavy, but actu­ally, it is just a big name for a way to organ­ize the inform­a­tion you need to have to ana­lyze and design the safety sys­tems for your machinery. Note that I am assum­ing that you are doing this in…

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ISO 13849 – 1 Analysis — Part 1: Start with Risk Assessment

This entry is part 1 of 9 in the series How to do a 13849 – 1 ana­lys­is

This post was updated 2019-07-24 I often get ques­tions from cli­ents about how to get star­ted on Func­tion­al Safety using ISO 13849. This art­icle is the first in a series that will walk you through the basics of using ISO 13849. Keep in mind that you will need to hold a copy of the 3rd edi­tion of ISO 13849 – 1 [1]…

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Testing Emergency Stop Systems

This entry is part 11 of 16 in the series Emer­gency Stop

I’ve had a num­ber of ques­tions from read­ers regard­ing test­ing of emer­gency stop sys­tems, and par­tic­u­larly with the fre­quency of test­ing. I addressed the types of tests that might be needed in anoth­er art­icle cov­er­ing Check­ing Emer­gency Stop Sys­tems. This art­icle will focus on the fre­quency of test­ing rather than the types of tests. The Prob­lem Emer­gency…

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CSA Z432 Safeguarding of Machinery – 3rd Edition

If you build machinery for the Cana­dian mar­ket, or if you modi­fy equip­ment in Cana­dian work­places, you will be famil­i­ar with CSA Z432, Safe­guard­ing of Machinery. This stand­ard has been around since 1992, with the last major revi­sion pub­lished in 2004. CSA has recon­vened the Tech­nic­al Com­mit­tee respons­ible for this import­ant stand­ard to revise the…

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