Control Functions

Interlock Architectures – Pt. 1: What do those categories really mean?

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Basic Stop/Start Circuit
This entry is part 1 of 8 in the series Cir­cuit Archi­tec­tures Explored

In 1995 CEN pub­lished an import­ant stand­ard for machine build­ers – EN 954 – 1, Safety of Machinery – Safety Related Parts of Con­trol Sys­tems – Part 1: Gen­er­al Prin­ciples for Design. This stand­ard set the stage for defin­ing con­trol reli­ab­il­ity in machinery safe­guard­ing sys­tems, intro­du­cing the Reli­ab­il­ity cat­egor­ies that have become ubi­quit­ous. So what do these cat­egor­ies mean, and how are they applied under the latest machinery stand­ard, ISO 13849 – 1?

Control Functions

Interlock Architectures – Pt. 4: Category 3 – Control Reliable

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Category 3 Architecture Logic Block Diagram
This entry is part 4 of 8 in the series Cir­cuit Archi­tec­tures Explored

Cat­egory 3 sys­tem archi­tec­ture is the first cat­egory that could be con­sidered to have sim­il­ar­ity to “Con­trol Reli­able” cir­cuits or sys­tems as defined in the North Amer­ic­an stand­ards. It is not the same as Con­trol Reli­able, but we’ll get to in a sub­sequent post. If you haven’t read the first three posts in this series, you may […]

Control Functions

Interlock Architectures – Pt. 5: Category 4 — Control Reliable

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This entry is part 5 of 8 in the series Cir­cuit Archi­tec­tures Explored

Ed. note: I’ve made a few updates to this art­icle since it was first pub­lished in 2011, with the most recent today, 6‑Dec-18. – DN – The most reli­able of the five sys­tem archi­tec­tures, Cat­egory 4 is the only archi­tec­ture that uses mul­­tiple-fault tol­er­ant tech­niques to help ensure that com­pon­ent fail­ures do not res­ult in an unac­cept­able […]

Control Functions

Interlock Architectures Pt. 6 – Comparing North American and International Systems

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industrial Control Console
This entry is part 6 of 8 in the series Cir­cuit Archi­tec­tures Explored

I’ve now writ­ten six posts, includ­ing this one, on the top­ic of cir­cuit archi­tec­tures for the safety-related parts of con­trol sys­tems. In this post, we’ll com­pare the Inter­na­tion­al and North Amer­ic­an sys­tems. This com­par­is­on is not inten­ded to draw con­clu­sions about which is “bet­ter”, but rather to com­pare and con­trast the two sys­tems so that […]

Control Functions

Inconsistencies in ISO 13849 – 1:2006

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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. If you look at Cat­egory 2 in Fig­ure 5, you will notice […]

Control Functions

31-Dec-2011 – Are YOU ready?

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

31-Decem­ber-2011 marks a key mile­stone for machine build­ers mar­ket­ing their products in the European Uni­on, the EEA and many of the Can­did­ate States. Func­tion­al Safety takes a pos­it­ive step for­ward with the man­dat­ory applic­a­tion of EN ISO 13849 – 1 and ‑2. As of 1‑Janu­ary-2012, the safety-related parts of the con­trol sys­tems on all machinery bear­ing a CE Mark will be […]