Hello.
I am planning to use a RFID antenna in a Zone 0 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 barrier) in order to make it intrinsically safe? Thanks!

 

You cannot make a component of an electrical circuit Intrinsically Safe by simply adding bits to the circuit - the inductance and capacitance of the total circuit need to be known and controlled. For Zone 0 use, you also need a circuit that is safe with 2 faults present - this applies to both the antenna in the flammable atmosphere and the energy limiting circuits in the power source.

To solve your problem, you will need:

1) an antenna that is certified as Ex ia

2) a drive circuit that is also certified as safe to [Ex ia] - braces indicate it is associated apparatus

3) documentation confirming that 1) and 2) are safe when used with each other

OR

Entity parameter information for the antenna and the driver, with calculations verifying that the voltage and current capable of being supplied to the antenna are less than the levels it is safe with, and the total inductance and capacitance of the antenna and interconnecting cable (and anything else downstream of the driver circuit) are less than the safe limit for the power source.

I don't think it is a good idea to attempt to design and build this for yourself - try and find a supplier who can meet the requirements...

Bruce

 

perhaps you could locate it inside of a pressurized enclosure.

 

Is your RFID antenna rated for use within a Zone 0 environment?

If so, the manufacturer will provide a 'Control Drawing' that shows how to provide adequate protection for the classified environment it is rated for. Use this 'Control Drawing'.

The NEC requires all electrical equipment within a classified environment to be rated for that environment. It will have been tested and will be marked as suitable. If it is not labeled as rated for Zone 0, you will not be in compliance with the NEC if you use it.

 

Do you really need something certified for Zone 0? Designing for Zone 1 will be easier/cheaper. That part of a classic plant that is actually really Zone 0 is normally only a small % of the total area.

Does the RFID antenna contain any active components or large values of inductance/capacitance?

Is this a one off or are you hoping to repeat the application?

Steve

Steve YATES
MTL Instruments, Luton, UK
Hazardous Area Blog - www.mtlblog.com

 

Good comments everyone. Yes, clearly going down the certification path is a big pain (and $$).

A clarification on the application would be good. Actually, it is only the antenna which is in the Zone0 classified area. It is connected to a reader which is in a non-classified area. As such, we know two things:
1) The antenna itself has to be certified
2) The reader is an associated apparatus and has to certified as such, meaning (please correct me if I am wrong) that only the portion of the circuit that is connected to the antenna.

So when I say "build", I mean add circuitry to the reader that complies with this requirement. The other option is to use a IS barrier but that is way too costly in this application. If you do not consider for a moment the cost of the certification (which should be one time), then there is not comparing the cost of a IS unit and the discrete components that make one up (i.e. it is not the components that are expensive...). So I care about BOM, not NRE...

Having said that, any ideas?

 

What is the signal that will be applied to the antenna (voltage/current/frequency)? Which country is this to be used in?

Steve

 

Well, the current and voltage are still TBD, and depend on the RF portion of the reader circuit and antenna design. But for sure it is low power as it is used for inductive coupling and the frequency is 125KHz.

 

If you are only talking 125Khz you may find that commercially available barriers will work in that application. This will be a far cheaper solution leaving you to worry about the antenna.

Steve

Steve YATES
MTL Instruments, Luton, UK
Hazardous Area Blog - www.mtlblog.com

 

Thanks. Any idea of some sources or keywords to search for? All I can find are rail mounted devices that don't really suit our requirement (and are very costly).

 

I really think you would be better off buying an off the shelf product and putting in an enclosure with suitable connectors. It will work out far cheaper than certifying your own design.

Whilst you will find basic circuits on the Internet, none of the manufacturers will give you detailed circuits or BOMs as that is how they (inc MTL) make their money.

Steve

 

I just saw this post while trolling for something else.

My company has been involved in getting a 125KHz RFID Reader Control Unit and antenna IECEx Approved for the past four years.
We are close to getting the IECEx certificate, but I cannot measure how many weeks "close" is.
The actual design of the RFID component is simple for us. We have been designing and manufacturing stationary and handheld RFID Readers for seven years.

The sourcing of the correct materials, the testing of the materials by the approval lab, the documentation, and the time the approval lab takes to test, measure, report etc is what takes the time. There are no short cuts, it is not tremendously expensive in dollar terms, but it is very expensive in time.

Regards

Mark Powell
General Manager
EDiT iD Limited
Auckland, New Zealand