[ RadSafe ] Interlock question

[JPreisig at aol.com]

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.  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.
 
   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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