EU changes direction on EN ISO 13849 – 1

Update on EN ISO 13849 – 1 man­dat­ory imple­ment­a­tion date.

In a post on 15-​Sep I repor­ted that the European Union had decided to delay the man­dat­ory imple­ment­a­tion date of  EN ISO 13849 – 1 for an addi­tion­al three years. This report was based on inform­a­tion obtained from an intern­al source at the European Commission and has since been reversed by that same source.

Mr. Glyn Garside provided the fol­low­ing update to this import­ant story:

It has been widely repor­ted, but nev­er con­firmed, that the EU com­mis­sion had accep­ted the CEN pro­pos­al to extend the date of ces­sa­tion of pre­sump­tion of con­form­ity of EN 954 – 1:1996 until the end of 2012. THESE REPORTS HAVE NOW BEEN AUTHORITATIVELY DENIED.

(By the way, this dis­cus­sion of dates of ces­sa­tion of pre­sump­tion of con­form­ity only affects the European stand­ards, EN 954 – 1 and EN ISO 13849 – 1. International stand­ard ISO 13849 – 1 is obvi­ously con­trolled by ISO and not by CEN or the EU. The cur­rent edi­tion of ISO 13849 – 1 is 2006, essen­tially identic­al to EN ISO 13849 – 1 : 2008.)

At this point the pos­sib­il­ity of an exten­sion of the trans­ition from EN 954 – 1 to EN ISO 13849 – 1 remains con­tro­ver­sial, con­fused and IMHO uncer­tain. (There’s been approx 3 years trans­ition peri­od already.) If I were still a man­u­fac­turer, I would not want to wait until Dec 29th to find out if I could still ship my product using EN 954 – 1!

The reports of an exten­sion were based on an email sent earli­er this month (3rd Sept) by a CEN employ­ee. However, the EU Commission nev­er con­firmed the report, and on September 24th the same CEN employ­ee, Marie Poidevin, has writ­ten,
— —  —  —  — –
> “We have been informed today by the European Commission […] that con­trary to what was expressed in
> my pre­vi­ous mes­sage sent on the 3rd of September, EN 954 – 1 will not give pre­sump­tion of con­form­ity
>  to the new MD 2006/​42/​EC until fur­ther notice.
> “Indeed, due to dis­cus­sions fol­low­ing the announce­ment made below, the EC wishes to gath­er experts’
> views and, there­fore, this issue will be dis­cussed at the next Machinery Working group to be held on
> the 7 – 8th December.”
— —  —  —  — –

A related email from Ian Fraser (“EC Policy Director for the Machinery Directive”), dated 2009-​09-​18 states,
— —  —  —  — –
“Following the dis­cus­sion at the meet­ing of the Machinery Working Group held on 7 and 8
July 2009, we have received a num­ber of ques­tions con­cern­ing the trans­ition from stand­ard
EN 954 – 1 to stand­ard EN ISO 13849 – 1 on safety-​related parts of con­trol sys­tems.
At the meet­ing of the Machinery Working Group, there was gen­er­al agree­ment on two
1. Manufacturers who apply stand­ard EN ISO 13849 – 1 bene­fit from a pre­sump­tion of
con­form­ity, even if the har­mon­ised C-​type stand­ard relat­ing to the machinery con­cerned still
refers to the cat­egor­ies of EN 954 – 1;
2. Harmonised C-​type stand­ards that refer to the cat­egor­ies of EN 954 – 1 con­tin­ue to con­fer a
pre­sump­tion of con­form­ity until they are amended to refer to stand­ard EN ISO 13849 – 1.
These con­clu­sions will be recor­ded in the minutes of the meet­ing.

During the dis­cus­sion, sev­er­al par­ti­cipants indic­ated that more time was needed for the
industry, and in par­tic­u­lar for SMEs, to adapt to the new stand­ard. As Chairman of the
meet­ing, I asked wheth­er it might not be prefer­able to post­pone the date of ces­sa­tion of
pre­sump­tion of con­form­ity for EN 954 – 1.
In response to this sug­ges­tion, on 30 July 2009, Mr. Steiger wrote to the Commission, on
behalf of the CEN Machinery Sector, to request that the date of ces­sa­tion of pre­sump­tion of
con­form­ity for EN 954 – 1 be excep­tion­ally post­poned until 31 December 2012 […].
The Commission will reply to this request from CEN. However, giv­en the com­plex­ity of the
issues involved, the Commission intends to con­sult experts and to seek the opin­ion of the
Machinery Working Group to be held on 7 and 8 December 2009, before reach­ing a final
Kind regards,
— —  —  — —

Thanks again to Glyn Garside and the EMC-​PSTC List Server!

Why Conventional EMC Testing is Insufficient for Functional Safety

At the recent PSES Symposium, I atten­ded a couple of inter­est­ing work­shops on EMC and Functional Safety. One was called “Workshop on EMC & Functional Safety” presen­ted by Keith Armstrong, Bill Radasky and Jacques Delaballe. The oth­er was a paper present­a­tion called “Why Conventional EMC Testing is Insufficient for Functional Safety” presen­ted by Keith Armstrong. 

For read­ers who are new to the idea of Functional Safety, this field deals

At the recent PSES Symposium, I atten­ded a couple of inter­est­ing work­shops on EMC and Functional Safety. One was called “Workshop on EMC & Functional Safety” presen­ted by Keith Armstrong, Bill Radasky and Jacques Delaballe. The oth­er was a paper present­a­tion called “Why Conventional EMC Testing is Insufficient for Functional Safety” presen­ted by Keith Armstrong.

For read­ers who are new to the idea of Functional Safety, this field deals with the abil­ity of a product or sys­tem to func­tion in it’s inten­ded use envir­on­ment, or in any fore­see­able use envir­on­ments, while reli­ably provid­ing the pro­tec­tion required by the users. Here’s the form­al defin­i­tion taken from IEC 61508 – 4:1998:

func­tion­al safety
part of the over­all safety relat­ing to the EUC and the EUC con­trol sys­tem which depends on the cor­rect func­tion­ing of the E/​E/​PE safety-​related sys­tems, oth­er tech­no­logy safety-​related sys­tems and extern­al risk reduc­tion facil­it­ies

equip­ment under con­trol (EUC)
equip­ment, machinery, appar­at­us or plant used for man­u­fac­tur­ing, pro­cess, trans­port­a­tion, med­ic­al or oth­er activ­it­ies

NOTE – The EUC con­trol sys­tem is sep­ar­ate and dis­tinct from the EUC.

Table 1: (E/​E/​PE) elec­tric­al /​ elec­tron­ic /​ pro­gram­mable elec­tron­ic

Reliability require­ments are found in two key stand­ards, ISO 13849 and IEC 61508. These two stand­ards over­lap to some degree, and do not define reli­ab­il­ity cat­egor­ies in the same way, which fre­quently leads to con­fu­sion. In addi­tion there is a Machinery Sector Specific stand­ard based on IEC 61508, called IEC 62061, Safety of machinery – Functional safety of safety-​related elec­tric­al, elec­tron­ic and pro­gram­mable elec­tron­ic con­trol sys­tems. These three stand­ards make ref­er­ence to EM effects on sys­tems but do not provide guid­ance on how to assess these phe­nom­ena. This is where IEC TS 61000−1−2 comes into play.

All three experts are mem­bers of IEC TC 77 and are dir­ectly engaged in writ­ing the second edi­tion of IEC TS 61000−1−2 (more info on this at the bot­tom of this post). This IEC Technical Specification deals with elec­tro­mag­net­ic (EM) effects on equip­ment that res­ult in func­tion­al safety prob­lems, like fail­ures in guard­ing cir­cuits, or fail­ures in some of the new pro­gram­mable safety sys­tems. This is becom­ing an increas­ingly import­ant issue as pro­gram­mable con­trols migrate into the tra­di­tion­ally hard­wired safety world. In fact, Keith poin­ted out that EM effects are present even in many of our “tried and true” cir­cuits, but the fail­ures have been incor­rectly attrib­uted to oth­er phe­nom­ena because most elec­tric­al engin­eers have not been used to think­ing about these phe­nom­ena, espe­cially in 24Vdc relay-​based con­trol cir­cuits.

In the work­shop, the presenters dis­cussed a typ­ic­al product life cycle, then went on to explore the typ­ic­al envir­on­ments that a product may be exposed to, includ­ing the EM and phys­ic­al envir­on­ments. They went on to dis­cuss the need for an EMC-​related Risk Assessment and then fin­ished up by look­ing at Electromagnetic Safety Planning. The whole work­shop took the entire second day of the Symposium.

A key point in the work­shop is that con­ven­tion­al EMC test­ing can­not prac­tic­ally prove that sys­tems are safe. This is due to the struc­ture of the EMC tests that are nor­mally under­taken, includ­ing the use of fixed mod­u­la­tion fre­quen­cies dur­ing immunity test­ing, fail­ure to assess inter­mod­u­la­tion effects and many oth­er issues. In addi­tion, EMC test­ing does not and can­not test for aging effects on per­form­ance, wear & tear and oth­er use-​related con­di­tions. The presenters dis­cussed a num­ber of ways that these prob­lems could be addressed and ways that test­ing could be exten­ded in select­ive ways to attack pre­dicted vul­ner­ab­il­it­ies. EMC test­ing does not con­sider the reli­ab­il­ity require­ments of the tested product (i.e. IEC 61508 – 1 SIL-​3 or SIL-​4).

On the fol­low­ing morn­ing, Keith Armstrong presen­ted his paper. In this paper, Mr. Armstrong went into con­sid­er­able detail on the short­com­ings of con­ven­tion­al EMC test­ing when it comes to Functional Safety. He sug­ges­ted some approaches that could be used by man­u­fac­tur­ers to address these issues in safety crit­ic­al applic­a­tions.

The work­shop present­a­tions and Mr. Armstong’s paper can be pur­chased through IEEE Xplore for those that did not attend the Symposium.

The IET has pub­lished a new book, avail­able for free from their web site, entitled Electromagnetic Compatibility for Functional Safety. This guide will be reviewed in a future post, so keep read­ing!

Keith Armstrong, Bill Radasky and Jacques Delaballe are mem­bers of IEC Technical Committee 77, writ­ing IEC TS 61000−1−2 Ed 2.0, ELECTROMAGNETIC COMPATIBILITY (EMC) – PART 1 – 2: GENERALMETHODOLOGY FOR THE ACHIEVEMENT OF THE FUNCTIONAL SAFETY OF ELECTRICAL AND ELECTRONIC EQUIPMENT WITH REGARD TO ELECTROMAGNETIC PHENOMENA. Edition 2 of this stand­ard should be pub­lished by Mar-​2009 accord­ing to the IEC.

Keith Armstrong is Principal Consultant at Cherry Clough Consultants in Brocton, UK.

Bill Radasky works with Metatech Corporation from his office in Goleta, California.

Jacques Delaballe works for Schneider Electric Industries SAS in Grenoble, France.

2008 IEEE PSES Symposium On Product Compliance Engineering

What a great Symposium! Dr. June Andersen kicked it off with a great key­note, and the rest of the ses­sions were excel­lent!

Last week I was at the 2008 PSES Symposium in Austin Texas.

This was one of the most suc­cess­ful Symposia held by the PSES, with 180 in attend­ance and 15 exhib­it­ors in the hall. Attendees came from as far as Argentina, the UK and Israel!

Dr. June Andersen gave a great key­note address on Monday morn­ing, show­ing the group how IBM man­ages world­wide com­pli­ance in more than 180 dif­fer­ent mar­kets. Dr. Andersen’s back­ground is impress­ive, and a bit intim­id­at­ing. I found her to be a warm, friendly and inter­est­ing per­son when we shared break­fast togeth­er before the con­ferece opened. Dr. Andersen’s present­a­tion will be made avail­able through the PSES web site to mem­bers, so if you would like a copy and you’re not a mem­ber, now is a great time to join!

Keith Armstrong of Cherry Clough Consultants, along with his col­leagues Jacques Delaballe and Bill Radasky presen­ted an inter­est­ing one-​day work­shop on EMC and Functional Safety, dis­cuss­ing the effects of EMC on the safety related parts of con­trol sys­tems. On Wednesday, Keith com­pleted the series with a short present­a­tion on the short­com­ings of con­ven­tion­al EMC test­ing in reveal­ing safety-​related design prob­lems. Definitely a worth­while series! Armstron, Delaballe and Radasky are plan­ning a new work­shop for next-year’s Symposium in Toronto that will carry on from this year, so if you are inter­ested in this area, plan to attend!

There were sev­er­al ses­sions on bat­ter­ies and the on-​going work that the bat­tery com­pan­ies and the main bat­tery con­sumers are under­tak­ing to resolve the design and man­u­fac­tur­ing prob­lems that led to the note­book and cell phone fires in the past year. These ses­sions were packed and well reviewed by every­one I spoke with.

There were lots of oth­er present­a­tions that I didn’t get a chance to attend – with 40 present­a­tions and only one me, it was impossible to get to every one.

If you missed this year’s Symposium, start plan­nng for next year’s in Toronto – it’s going to be great!