[ RadSafe ] Interlock question
JPreisig at aol.com
JPreisig at aol.com
Thu Oct 30 23:01:34 CDT 2014
Radsafe,
A EE who cannot design a fundamental interlock system is in serious
career trouble. I had a friend from Buffalo (USA) who had sufficient high
school technology instruction to design nand, nor, and etc. gate circuits in
high school. I was so awed by him. Joe Shonka's comments on interlock
technology are soooo
interesting and workable. I begin to wonder why some Health Physics
Department has not given Joe Shonka a Research Assistant/Associate Professorship
at their school. WTF.
Joe Preisig
In a message dated 10/30/2014 11:51:29 P.M. Eastern Daylight Time,
tdc at xrayted.com writes:
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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