Inconsistencies in ISO 13849–1:2006

Posted by on November 10, 2011 1 comment
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  (kennedyatisodotorg)  . More details on ISO TC199 can be found on the Technical Committee page on the ISO web Site.

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Bye, Steve. Thanks for everything!

Posted by on October 6, 2011 3 comments

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
dnixatmacdotcom

http://​www​.world​his​tory​.com/​w​i​k​i​/​A​/​A​p​p​l​e​-​e​v​a​n​g​e​l​i​s​t​.​htm

Standards in Music

Posted by on October 5, 2011 Comments Off

Working in a field that is stan­dards heavy, I often get ques­tions from clients and stu­dents about the ori­gin of stan­dards. Recently I heard a dis­cus­sion on CBC radio talk­ing about the ori­gins of musi­cal nota­tion, and I real­ized that this is prob­a­bly one of the ear­li­est exam­ples of stan­dard­iza­tion. Here’s the story as I under­stand it.

In the early days of the Holy Roman Empire, Pope Gregory I, who sat as Bishop of Rome from 590 to 604, decided that there was a polit­i­cal need to solid­ify Rome’s hold on Catholic Christian com­mu­ni­ties. All of these com­mu­ni­ties used the same Latin liturgy, but the music that was used when singing parts of the Mass var­ied from church to church and monastery to monastery. To help con­sol­i­date Rome’s hold, the deci­sion was made that all of the com­mu­ni­ties should use the same music. Eliminating the local vari­a­tions in music would show Rome’s power and help to unify the com­mu­nity. The prob­lem was that there was no means to com­mu­ni­cate music in writ­ing, and rely­ing strictly on the mem­ory of the field agents was not the most reli­able means. Some means of con­vey­ing music in writ­ten form was required.

Someone in Rome devel­oped the ear­li­est method for writ­ing music down, but the exact per­son who came up with the sys­tem is unknown, lost in time.  The ear­li­est records only show increases and decreases in pitch, with no infor­ma­tion on dura­tion, rhythm or pace. This sys­tem used marks called “neumes”.

Early musical notation

Neume musi­cal notation

From this early sys­tem grew the com­plex nota­tion that is now used to com­mu­ni­cate music, a stan­dard­ized sys­tem used world-​​wide for com­mu­ni­cat­ing west­ern music.

So how old is stan­dard­iza­tion? Based on this story, at least 1500 years!

Do you have a story about the ori­gins of stan­dard­iza­tion or a par­tic­u­lar stan­dard? Share it with us by leav­ing a comment!

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