Inconsistencies in ISO 13849–1:2006

This entry is part 7 of 8 in the series Cir­cuit Archi­tec­tures Explored

I’ve writ­ten quite a bit recent­ly on the top­ic of cir­cuit archi­tec­tures under ISO 13849–1, and one of my read­ers noticed an incon­sis­ten­cy between the text of the stan­dard and Fig­ure 5, the dia­gram that shows how the cat­e­gories can span one or more Per­for­mance Lev­els.

ISO 13849-1 Figure 5
ISO 13849–1, Fig­ure 5: Rela­tion­ship between Cat­e­gories, DC, MTTFd and PL

If you look at Cat­e­go­ry 2 in Fig­ure 5, you will notice that there are TWO bands, one for DCavg LOW and one for DCavg MED. How­ev­er, read­ing the text of the def­i­n­i­tion for Cat­e­go­ry 2 gives (§6.2.5):

The diag­nos­tic cov­er­age (DCavg) of the total SRP/CS includ­ing fault-detec­tion shall be low.

This leaves some con­fu­sion, because it appears from the dia­gram that there are two options for this archi­tec­ture. This is backed up by the data in Annex K that under­lies the dia­gram.

The same con­fu­sion exists in the text describ­ing Cat­e­go­ry 3, with Fig­ure 5 show­ing two bands, one for DCavg LOW and one for DCavg MED.

I con­tact­ed the ISO TC199 Sec­re­tari­at, the peo­ple respon­si­ble for the con­tent of ISO 13849–1, and point­ed out this appar­ent con­flict. They respond­ed that they would pass the com­ment on to the TC for res­o­lu­tion, and would con­tact me if they need­ed addi­tion­al infor­ma­tion. As of this writ­ing, I have not heard more.

So what should you do if you are try­ing to design to this stan­dard? My advice is to fol­low Fig­ure 5. If you can achieve a DCavg MED in your design, it is com­plete­ly rea­son­able to claim a high­er PL. Refer to the data in Annex K to see where your design falls once you have com­plet­ed the MTTFd cal­cu­la­tions.

Thanks to Richard Har­ris and Dou­glas Flo­rence, both mem­bers of the ISO 13849 and IEC 62061 Group on LinkedIn for bring­ing this to my atten­tion!

If you are inter­est­ed in con­tact­ing the TC199 Sec­re­tari­at, you can email the Sec­re­tary, Mr. Stephen Kennedy. More details on ISO TC199 can be found on the Tech­ni­cal Com­mit­tee page on the ISO web Site.

Bye, Steve. Thanks for everything!

Today marks a turn­ing point for me. With the loss of Steve Jobs, the world is a less­er place. His bril­liance, vision and charis­ma changed the world for the bet­ter in so many ways.

Bye SteveAs any­one who knows me well will tell you, I am a pas­sion­ate Mac user. I became a believ­er in 1991 when my then-girl­friend intro­duced me to her SE-30, “Peanut”, but my his­to­ry with Apple goes back all the way to 1980. As a Grade 10 stu­dent, I land­ed a job sell­ing Apple com­put­ers. We were sell­ing Apple II’s, II+‘s, IIe’s and III’s in those days. The Apple II was the first game chang­er from Apple, deliv­ered in the days when com­put­ers were behe­moths owned by cor­po­ra­tions, and the Uni­ver­si­ty of Waterloo’s Red Room was the heart of their com­put­er sci­ence pro­gram. I remem­ber the launch of the Lisa, and I remem­ber my first expe­ri­ence of a graph­i­cal UI on the Lisa we had in the show­room.

I became an Evan­ge­Lista in the ’90’s, sub­scrib­ing to the Mac Evan­ge­List pub­lished by Guy Kawasa­ki. Armed with GK’s facts, I went armed into bat­tle with my PC lov­ing col­leagues. I watched in hor­ror as Scul­ley oust­ed Steve from Apple, and the com­pa­ny entered a peri­od of medi­oc­rity that near­ly end­ed it when Gil Ame­lio took charge and in a stroke of vision­less lead­er­ship insist­ed on build­ing the same crap­py beige box­es that every­one else was build­ing.

My evan­ge­lism nev­er slack­ened, despite these set­backs, despite the crit­i­cism and doom­say­ing of friends, fam­i­ly and col­leagues. I con­tin­ued to pick fights with PC users who just didn’t, and couldn’t, “get it”.

My heart soared when Steve came back to Apple, and the launch of the first iMacs in Bon­di Blue changed the world. It was the begin­ning of the rev­o­lu­tion I always knew would come. My Bon­di Blue Rev B iMac still works, and has a safe place in my house, as a reminder of what change can look like.

As I sit writ­ing this on my 27″ I5 iMac, I am in awe of what great lead­er­ship can do. To say that I am inspired by Steve Jobs leaves it a lit­tle short.

So this year I’ll add Octo­ber the 5th to my Mac cal­en­dar, next to Jan­u­ary 24th, 1985, as a key date in my cal­en­dar. I’ll remem­ber and be inspired by Steve’s words and actions as a great leader, a great busi­ness­man, and a great per­son. I’ll try to make my life a lit­tle sim­pler and a lit­tle clear­er, fol­low­ing his lead, and I’ll say “Thanks for every­thing, Steve. We’ll miss you!”.

Doug Nix — Mac­in­tosh Evan­ge­lista

CSA Z462 — Workplace Electrical Safety Public Review

CSA Z462 — Work­place Elec­tri­cal Safe­ty is now avail­able for pub­lic review on the CSA web site. This stan­dard is the Cana­di­an imple­men­ta­tion of NFPA 70E and IEEE P1584, cov­er­ing elec­tro­cu­tion and arc-flash haz­ards in the work­place.

Pub­lic Review Draft of Z462-12

Because of the impor­tance of the Z462 Stan­dard to the elec­tri­cal sec­tor, CSA staff have decid­ed to set up the draft on the new On-line Pub­lic Review Sys­tem. This sys­tem is inte­grat­ed with sev­er­al on-line social net­works and has been made avail­able to a wide inter­na­tion­al audi­ence. Auto­mat­ic noti­fi­ca­tion will go out to all peo­ple and orga­ni­za­tions that have expressed inter­est in CSA’s elec­tri­cal stan­dards (thou­sands of stake­hold­ers).

There are two major dif­fer­ences in the way this new on-line review sys­tem works:

1.       The review­er must first reg­is­ter with the sys­tem to gain access to the draft stan­dards (name, affil­i­a­tion, coun­try, and e-mail address).

- the review­er must have a valid e-mail address (iden­ti­ty)

2.       The doc­u­ment is only avail­able on-line (no down­load) and it is review­able only in pieces for com­ment­ing pur­pos­es.

- sim­i­lar to the mem­bers’ bal­lot com­ments, the sys­tem auto­mat­i­cal­ly col­lects and sorts the com­ments by clause num­ber.

Note: the new review page is also acces­si­ble via a link locat­ed at the top of the old Review Page ( – iden­ti­fied as “New: …Elec­tri­cal pub­lic review drafts”.

For more infor­ma­tion on this stan­dard, please con­tact the CSA Project Man­ag­er, Mr. Dave Shana­han,, or call him at 1–800-463‑6727.