[ RadSafe ] Interlock question

Ted de Castro tdc at xrayted.com
Thu Oct 30 15:23:24 CDT 2014

Thanks Bob - I'll look that over.  Yet my question is still with regards 
to more primitive electronics - discrete logic, gates, buffers etc. be 
it TTL or CMOS or whatever.  These are vulnerable yet not as engineered 
and thought out as a safety certified PLC - but certainly less 
complicated and don't involve software.

I don't see a compelling need to employ such in interlock circuits and 
thus prefer to stay with the tried and true, and easy to analyze and 
test, switches and relays.  It doesn't matter if failure is more 
frequent - if by design that failure is failsafe - and better yet 

Like I said - I couldn't get consensus on that from the writing 
committee on ANSI N43.2.  Its hard to say why.


On 10/30/2014 11:21 AM, Bob May wrote:
> Excellent discussion on interlock design and functionality. There is a Rockwell publication at the following link: http://discover.rockwellautomation.com/Files/PLC-vs-Safety-PLC-Fundamental-and-Significant-Differences.pdf that discusses PLCs versus Safety PLCs. It won't change your mind if you are not a fan of electronic systems but it is informative and points to the international standard IEC 61508, "Functional safety of electrical/electronic/programmable electronic safety-related systems".
> Bob
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