EX rated micro switch

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Ok, this is not an AVR related question, but project does off course contain an AVR so here it goes anyway.

Our project needs to be EX-rated and for one of its function we might need to design in an micro-switch, so question is if any of you have seen EX rated micro switches and from which manufactures.

Hopes someone can help

Regards
Vidar (Z)

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"The fool wonders, the wise man asks"

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What's EX-rated? Is that an atmosphere rating like GX?

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Think it's got to do with being certified for use in environments containing hazardous vapours.

(ie. he needs a switch that's certified not to arc and blow up all the fumes in his meth lab? j/k =)

Clancy _________________ Step 1: RTFM Step 2: RTFF (Forums) Step 3: RTFG (Google) Step 4: Post

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I was able to found few items from RS:
http://www.rsfinland.com/cgi-bin...@@@@0323217278.1162855369@@@@&BV_EngineID=cccdaddjfjmkeklcefeceeldgondhgg.0&cacheID=finetscape&Nr=avl:fi

Regards
heguli

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While such a thing as an explosion proof microswitch probably does indeed exist, you might think instead along the lines of making the design intrinsically safe. As long as the voltage and current going through the switch are below a certain level then it should be okay (won't touch off a perfect mixture of hydrogen and air). Easiest way to do that is to use intrinsic safety barriers to limit the current and voltage to safe levels.

See: http://www.am.pepperl-fuchs.com/...

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Thanks to all...

Using micro switch is only one of the possibilities considered. Other alternatives is to use for example magnetic switches (hall effect) or light, and others, however all technologies have to be considered and pos. neg. characteristics must be evaluated before we make any decisions. We have versions pr. to day which has used both hall effect and/or light detection, but there might be spurious magnetic fields or light which gives erroneous behavior which might not be so easy to get around, therefor we also considers switches, but these have to be EX rated.

Regards
Vidar (Z)

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"The fool wonders, the wise man asks"

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Hi,

what about REED?
There are small glass tubes with a switch inside.
If you place a magnet next to the tube - it switches.

Klaus
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Look at: www.megausb.de (German)
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Thanks, reeds are also considered but these are also sensitive to spurious magnetic fields and most of them is not selective when looking at the direction of the magnetic field. Most possible we need to use a combination of several techniques or require the magnetic field strength to be high so the chances for spurious fields of same strength can be neglected.

Switches is the technology with least problems except for the mechanical abrasion and problems/cost with manufacturing, they also tend to cost a whole lot more if they is to be EX rated. But for the lifetime of our product abrasion might be neglected.

Thanks anyway

Regards
Vidar (Z)

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"The fool wonders, the wise man asks"

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Firstly, when you're talking EX - what standard are we talking about? ATEX, IECeX, UL, CSA? If the application is for use in Norway, I would expect we're talking about ATEX. This is critical as something certified for use in the USA may not be suitable for use in Europe and vice-versa. Currently there is no worldwide standard.

You have two easy possibilities - neither are cheap! Get a switch that is either ExE or ExD rated or use a standard switch connected via a Exi barrier or galvanic isolator. Pepperl & Fuchs supply a variety of devices suitable for your use. Look at the KFA series of galvanic isolators - i've used a few of these.

You also need to consider how these items are installed, labelled and wired as well as the hazard (gas group, dust etc) - this is all outlined in the ATEX standards. There's a lot more than just getting a switch with the Ex label on it.

This is specialist stuff - you may want to employ the services of someone experienced in this field to avoid problems and legal issues.