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Rob Spiegel
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Re: But are the functions really separate?
Rob Spiegel   1/29/2014 2:10:26 PM
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William K, it should certainly be interesting. Thanks for the idea.

William K.
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Platinum
Re: But are the functions really separate?
William K.   1/29/2014 2:03:04 PM
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Rob, I am certain that it will gather a lot of attention and interest quite a few folks. Safety goes way beyond just being safe, it also seems to require that industrial equipment, at least, be guarded against those who are way beyond just incompetent. 

So it will be very interesting to see what some of the manufacturers, such as Siemens, have to say about thier safety systems.

Rob Spiegel
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Re: But are the functions really separate?
Rob Spiegel   1/29/2014 6:25:36 AM
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Well, Willliam K, perhaps the next step in our conversation on this subject is for me to go out and see what people are asying about this. So I'll do the story.

William K.
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Platinum
Re: But are the functions really separate?
William K.   1/28/2014 4:26:53 PM
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Ten years is probably a long enough time for that constantly repeated assertion to have taken on an " aura of correctness", no matter what. But all of those mechanisms for keeping the systems independant should be covered by patents now and so be something that can be discussed with the engineering community. And I am one who would really like to hear how a hardware fault in a processor only affects part of that processor. Of course, over the years, I have come across digital ICs that had partly failed, but not very many of them.

Rob Spiegel
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Re: But are the functions really separate?
Rob Spiegel   1/28/2014 11:47:24 AM
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Good point, WilliamK. The hype has been universal. It's been years since I have heard anyone argue for separate networks for control and safety. When I first covered this subject 10 years ago, the majority of plant operators I spoke with wanted separation. Now I don't hear anyone say that.

William K.
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Platinum
Re: But are the functions really separate?
William K.   1/27/2014 3:37:36 PM
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Thanks, that is why I suggested it. Probably quite a few engineers would want to see what the reality is, aside from the hype. How are those two functions kept independant and yet in the same box.

Rob Spiegel
User Rank
Blogger
Re: But are the functions really separate?
Rob Spiegel   1/27/2014 10:26:45 AM
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That's a great article idea, William K. I'll look into that.

William K.
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Platinum
Re: But are the functions really separate?
William K.   1/26/2014 4:48:28 PM
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I am certain that some of the potential failure modes have been avoided on the safety section of the all-in-one-system PLC packages, but short of being truly triple redundant it is not reasonable to anticipate that they are 100% safe. And it would be very worthwhile to read the actual user documentation and see what disclaimers and warnings are there that don't make it to the advertising areas. 

In short, when a set of claims are simply too good to be true, I usually doubt that they are true. That attitude has saved me from a couple of disasters over the years. 

taimoortariq
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Gold
Re: But are the functions really separate?
taimoortariq   1/25/2014 11:00:17 PM
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William, I understand your point. But I am sure that they must have done alot of rigourous experiments to check and finally verify the device, as SAFE. I mean I dont exactly know the internal architecture of the PLC security module, but if they are selling the product all around the world, they must have made it very robust under the fail conditions. Obviously, no system is 100% fool proof, but when they say that relatively this system is more reliable and safe then the other one. Than they must have made it more safer.

taimoortariq
User Rank
Gold
making lives easy
taimoortariq   1/25/2014 10:46:35 PM
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Nice Article Rob, Smarter PLC's certainly makes lives much easier. To get stuck with the setup and configuration problems can be quite time consuming and equally frustrating. To have every thing combined in one PLC is a treat for a control engineer.

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