[ RadSafe ] Interlock question

[Ted de Castro]

Unfortunately many electrical engineers seem blissfully unaware of the 
requirements and what constitutes and redundant failsafe interlock 
design - you'd be amazed at the of the EE designs I've seen and one that 
even cost a researcher 3 fingers.

Separation of disiplines would be great - unfortunately the HP gets 
asked to approve a piece of equipment and one cannot rely one "the 
engineer said so" but has to learn to do ones own analysis.


On 10/30/2014 2:42 PM, JPreisig at aol.com wrote:
> Radsafe:
>   
>       Transistors, gate technology (nand, nor,....),  integrated circuits,
> other digital circuitry, are explained in electronics books  such as Brophy,
> Diefenderfer, Malmstadt and Enke and newer texts.  If you  are unfami
> liar with this stuff read these books.  One should able to use such
> circuits, or perhaps even computer software, for interlock design.  If you  are
> uncomfortable with this technology, then do indeed use relays, switches and
> so on.  I expect both sets of technology can be used to surpass failure
> modes.  If there is some relevant technical standard, then try to keep to  the
> standard.  At Brookhaven Lab, Health Physicists do health physics,  shielding
> design and Electronics Engineers do interlock design.  Maybe some  HP's are
> also EE's.  (i.e. Steve Musolino).
>   
>       My Dad, Joseph O. Preisig, was a EE who did vacuum  tubes,
> transistors, color TV design, memory design, satellite work, night vision  goggle work,
> semiconductors, COS/MOS, power supplies etc. for many years with  RCA and
> Telefunken.  I, Joseph R. Preisig, do accelerator health physics,  neutron
> spectrometry, Monte Carlo modeling, geophysics, seismology, Kalman  Filtering,
> Electronics, NIM electronics, Fortran Programming and similar  things.
>   
>       If a standards committee is unwilling to deal with  someone, it may be
> because someone is severely old school in electronics and is  unwilling to
> accept some of the new technology.

X-ray machine interlocks are a matter of technically sound/safe design - 
not a current technology fashion statement!


>    If one is designing  interlocks to keep
> people from irradiating their fingers/hands, eyes, etc. in  XRay machines,
> then I hope/pray you are doing your job very well.

I do!

>   
>     A relatively unsupervised nuclear technican at Chernobyl  caused many
> folks considerable hardship and pain.
>   
>     Joe Preisig
>   
>     
>   
> In a mesvevelylysage dated milar things10/30/2014 4:23:52 P.M. Eastern
> Daylight Time, tdc at xrayted.com writes:
>
> 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
> detectable.
>
> Like I said - I couldn't get consensus on  that from the writing
> committee on ANSI N43.2.  Its hard to say  why.
>
> ted
>
>
>
>
> 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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