Safety barrier for RFID antenna?

I am planning to use a RFID antenna (reader) in a Zone 0 explosive
classified area, and it is connected to an apparatus which is located
in a non-classified zone. My question is, what type of circuit do I
need to build inside my equipment (i.e. not a separate unit) in order
to make it intrinsically safe? I know it has something to do with
zeners but I would appreciate some guidance and examples.

ElderUberGeek wrote:
> I am planning to use a RFID antenna (reader) in a Zone 0 explosive
> classified area, and it is connected to an apparatus which is located
[...]
> to make it intrinsically safe? I know it has something to do with
> zeners but I would appreciate some guidance and examples.

Okaaaaaaay... You do realize, this is probably the most hair-raising
post I've read in c.a.e. for quite a while? It's a bit like opening a
Little Golden Book and finding "Now, kids - once you've acquired your
UF6, you need to build a centrifuge cascade..."

larwe wrote:

> Okaaaaaaay... You do realize, this is probably the most hair-raising
> post I've read in c.a.e. for quite a while? It's a bit like opening a
> Little Golden Book and finding "Now, kids - once you've acquired your
> UF6, you need to build a centrifuge cascade..."

:-)
I can appreciate your apprehension.... BUT, I can assure you this is
acceptable industry use which has been done many times in the past and
will be done many times in the future (how do you think large
companies, for example, take stock say of LPG bottles in a filling
plant?). Seriously, I guess you are just not familiar with the
industry.

Any ideas anyone?

"ElderUberGeek" <aribloch@gmail.com> wrote in message 
news:1168905118.816139.319700@51g2000cwl.googlegroups.com...
>I am planning to use a RFID antenna (reader) in a Zone 0 explosive
> classified area, and it is connected to an apparatus which is located
> in a non-classified zone. My question is, what type of circuit do I
> need to build inside my equipment (i.e. not a separate unit) in order
> to make it intrinsically safe? I know it has something to do with
> zeners but I would appreciate some guidance and examples.

Whilst I'm not designing anything intrinsically safe myself at this 
time, it is possible that I might have to in the future so I watch these 
threads with interest. I'm guessing that the zeners are to dissipate 
energy that might be received from a big dollop of RF hitting the 
antenna?

I agree with Lewin that the OP is hair-raising at first glance but I do 
hope that someone will answer the question and that ElderUberGeek 
doesn't blow himself (or anyone else) up while implementing it. 

ElderUberGeek wrote:
> larwe wrote:
> 
>> Okaaaaaaay... You do realize, this is probably the most hair-raising
>> post I've read in c.a.e. for quite a while? It's a bit like opening a
>> Little Golden Book and finding "Now, kids - once you've acquired your
>> UF6, you need to build a centrifuge cascade..."
> 
> :-)
> I can appreciate your apprehension.... BUT, I can assure you this is
> acceptable industry use which has been done many times in the past and
> will be done many times in the future (how do you think large
> companies, for example, take stock say of LPG bottles in a filling
> plant?). Seriously, I guess you are just not familiar with the
> industry.
> 
> Any ideas anyone?

I think his (well, certainly my) concern was over the bits "I am 
planning to use a RFID antenna (reader) in a Zone 0 explosive
classified area" and "I know it has something to do with
zeners but..."

It's like the posts in uk.d-i-y saying "I'm in the middle of re-wriring 
my house - which colours are live and which are neutral? Cheers" or "I'm 
replacing my gas boiler - how do I turn off the gas?".  They just give 
the impression that the poster is trying something which has significant 
safety issues if implemented wrongly but only has a vague grasp of the 
concepts and no idea of the details.

Now, I've no idea who you are, what your experience is, and have no idea 
of your industry - it was more an explanation of why, at first reading, 
your post might ring some warning bells to readers.

Thanks

David

David Hearn wrote:
> ElderUberGeek wrote:
> > larwe wrote:
> >
> >> Okaaaaaaay... You do realize, this is probably the most hair-raising
> >> post I've read in c.a.e. for quite a while? It's a bit like opening a
> >> Little Golden Book and finding "Now, kids - once you've acquired your
> >> UF6, you need to build a centrifuge cascade..."
> >
> > :-)
> > I can appreciate your apprehension.... BUT, I can assure you this is
> > acceptable industry use which has been done many times in the past and
> > will be done many times in the future (how do you think large
> > companies, for example, take stock say of LPG bottles in a filling
> > plant?). Seriously, I guess you are just not familiar with the
> > industry.
> >
> > Any ideas anyone?
>
> I think his (well, certainly my) concern was over the bits "I am
> planning to use a RFID antenna (reader) in a Zone 0 explosive
> classified area" and "I know it has something to do with
> zeners but..."
>
> It's like the posts in uk.d-i-y saying "I'm in the middle of re-wriring
> my house - which colours are live and which are neutral? Cheers" or "I'm
> replacing my gas boiler - how do I turn off the gas?".  They just give
> the impression that the poster is trying something which has significant
> safety issues if implemented wrongly but only has a vague grasp of the
> concepts and no idea of the details.
>
> Now, I've no idea who you are, what your experience is, and have no idea
> of your industry - it was more an explanation of why, at first reading,
> your post might ring some warning bells to readers.
>
> Thanks
>
> David

Apart from that, there are two critical things missing.

1. Define 'Intrinsically safe'. This is probably specified for the area
classification, which brings us to:

2. What are the relevant national safety standards for such zones? Do
you have a copy of said specification?

If you don't know (2), then you need to find out or you probably
shouldn't be attempting this.

Cheers

PeteS

PeteS wrote:

> Apart from that, there are two critical things missing.
>
> 1. Define 'Intrinsically safe'. This is probably specified for the area
> classification, which brings us to:
>
> 2. What are the relevant national safety standards for such zones? Do
> you have a copy of said specification?
>
> If you don't know (2), then you need to find out or you probably
> shouldn't be attempting this.
>
> Cheers
>
> PeteS

Friends (David et-all), interesting how this has become (deteriorated?)
a discussion about safety, capabilities and understanding rather than
engineering...
Would everyone feel better if I had posted "I need to monitor the level
of gas in a mine shaft and need a barrier for the sensor", would that
have been less scary for you? :) All said, it is exactly the same
question... just a different (and relevant - not strange) item at the
end of the line....

To answer PeteS's question about the definition of Intrinsically Safe,
well, here is a link for everyone to read at leisure
(http://www.crouse-hinds.com/CrouseHinds/resources/intrinsically_safe/techref/article1.cfm)
but basically IS is one of the many methods of protection (as opposed
to Explosion Proof, for example) which is meant to keep electrical
circuits from igniting gases etc. by way of controlling the amount of
heat they dissipate or ability to spark etc.

Regarding standards, yes every area (zone/class/division etc.) has
various applicable standards that you have to comply with according to
the degree of protection required, zone etc. And yes, a copy of this is
essential reading for anyone looking to design such circuits (papers
are in the mail...).

So having, hopefully, satisfying everyone about the above, the question
remains: can anyone share any "practical" design inputs for
constructing barriers in intrinsically safe equipment....

(Phew.... i need a drink!)

ElderUberGeek wrote:
> I am planning to use a RFID antenna (reader) in a Zone 0 explosive
> classified area, and it is connected to an apparatus which is located
> in a non-classified zone. My question is, what type of circuit do I
> need to build inside my equipment (i.e. not a separate unit) in order
> to make it intrinsically safe? I know it has something to do with
> zeners but I would appreciate some guidance and examples.

Factory Mutual (FM) or ATEX requires double fault protection for Zone
0.

That means you'll have to limit the voltage and current to the antenna
to safe levels.... Low enough level so a spark will not occur if the
cable to the RFID antenna is cut. I don't know if they have a RF power
level requirement yet. Factory Mutual has Voltage vs Current graphs
that will let you know what you have to limit your DC levels to.

The most simple solution is to use three resistors in series each with
a shunt zener diode for limiting the voltage. The resistors limit the
current. The reason you need 3 is because of the tripple redundacy
required for double fault protection. Any two components could fail and
you'll still prevent a spark. Every wire going to the RFID antenna will
need this resistor and zener limiting circuit.

Eric

On 15 Jan 2007 15:51:59 -0800, "ElderUberGeek" <aribloch@gmail.com>
wrote:

>I am planning to use a RFID antenna (reader) in a Zone 0 explosive
>classified area, and it is connected to an apparatus which is located
>in a non-classified zone. My question is, what type of circuit do I
>need to build inside my equipment (i.e. not a separate unit) in order
>to make it intrinsically safe? I know it has something to do with
>zeners but I would appreciate some guidance and examples.

  I have been working on the design of RFID readers for alomost 10
years and strongly suggest you contact the manufacturer of the RFID
equipment with your questions.  There are numerous pieces of
information needed that only they can supply.  Some of them are:
1) what happens if the antenna becomes disconnected from the feed
cable inside the explosive area (is the RF power shut down?; if so,
how quickly?; if not, will the result violate requirements?)
2) is there a DC voltage applied to the cable to determine if the
proper antenna is attached or shorted or missing?  If so, will its
presence cause a violation of requirements?
  They, the original designers are ina much better position to work
with you in ensuring their product can be safely and legally used in
the environment you describe.

Regards
-Bill Knight
R O SoftWare

"ElderUberGeek" <aribloch@gmail.com> wrote in message 
news:1168905118.816139.319700@51g2000cwl.googlegroups.com...
>I am planning to use a RFID antenna (reader) in a Zone 0 explosive
> classified area, and it is connected to an apparatus which is located
> in a non-classified zone. My question is, what type of circuit do I
> need to build inside my equipment (i.e. not a separate unit) in order
> to make it intrinsically safe? I know it has something to do with
> zeners but I would appreciate some guidance and examples.
>

Depending on the number of units you are planning on using, it may be 
cheaper to just buy an IS barrier that can handle the voltage, current, 
capacitance, and inductance of your antenna.

I did an IS barrier a while back with lots of redundant SCR's and firing 
circuits  instead of zeners to lower our manufacturing costs, but the quote 
from CSA for testing was high enough that it was cheaper in our case to buy 
someone elses barrier.

If you have to roll your own, there are several good reference books at 
http://www.isa.org/

Mark Walsh
www.rogue-engr.com