Intrinsic safety

[darksky]

has anyone got any inforamtion on deisgning intrinscially safe equipment for use around gas?

This involves ATEX approval etc.

[50caliber]

Better start Google-ing, and there's probably not that much available.  You can start with FM Standard 3610 which may give general background requirements for IS equipment:

Code:

http://www.fmglobal.com/page.aspx?id=50030000
http://www.fmglobal.com/assets/pdf/fmapprovals/3610.pdf

More specific to ATEX, check out:

Code:

http://ec.europa.eu/enterprise/atex/guide/

What are you designing?  In general, IS is not difficult to achieve for most instrumentation.

[darksky]

I am looking to design a data logger to go on a commercial gas meter.

Thank you for the links - tried Google but not much detail  - found reference to EN60079 -0, -11,- 26

[50caliber]

The best general advice I can give is:

Keep the operating voltage as low as possible.  Keep capacitance and inductance values low.  ATEX requires triple redundancy i.e. 3 zener diodes at the points of protection. Oversize any series current limiting resistors in the power circuit.  Use proper PCB trace spacing per the standards.

Your first IS design will likely have problems when you submit it for certification.  Don't wory about it - Try to make a good working relationship with the examination engineer and revise the circuit as necessary.  It is best if you can discuss the design during prototyping, but this is not always possible since you have to open up a contract with the certification agency.

Most of my stuff goes through CSA, FM, and UL.  ATEX is generally a little more demanding.  Generally speaking, if it passes ATEX, if will easily pass the others.  Good luck with your design.