Control.com - Nerds in Control

i want to ask you people that if trnsmitter have no marking on it then how one can differentiate either it is explosion proof or intrinsically safe and suitable for which haz class & division & gas group?????

That's easy. If it has not got any markings, it fits into a third category
- it provides no protection of any form and cannot be used in an explosive atmosphere.

Even if you know it was once explosion protected, unless it is permanently marked with details of the protection methods (and under IEC rules with a lot of other information including at least the certificate number) it does not meet the standard required and cannot be used.

Bruce

There is a large misunderstanding of the concept of intrinsically safe/explosion proof. This deals with the understanding of use of electrical equipment in an area of (likely) concentration of hydrocarbons. To minimise the risk, the type of protection systems used are what are listed below:
EX(d)- flameproof (sometimes referred to as explosion proof)
Ex(e)- enhanced safety
Ex(p) - pressurized or purged type
Ex(n)- non incendive
Ex(ia) or Ex (ib) - intrinsic safety
Ex (s)- special.

When any equipment is used in these areas there are certain guidelines which dictate the pattern of their usage. Websites like Crouse-Hinds or Stahl give fantastic detail about the systems.

If a transmitter is not marked then it is definitely an ordinary transmitter that may not be used in hazardous areas directly. If at all the transmitter is capable of being driven through an intrinsically safe barrier (zener barrier) it may then be considered for usage in a class II zone.

If not or if the requirement is higher then the entire transmitter has to be housed inside an enclosure (box) that is rated Ex(d). The power supply to the transmitter has to be switched off if the enclosure is to be opened.

This also places requirements on the glands that penetrate the enclosure.

Largely a misunderstood area, I recommend that you go through the text offered in the above mentioned sites.

I am asking you this question as I want to use "used & refurbished instruments" in my refinery. If these types of instruments do not have any marking how would you differentiate b/w them? I mean explosion proof & intrinsically safe as both types of instruments have certain requirements which have to be met. So the question remains the same, how one can differentiate if Tx does not have any marking.

If they have no marking on them, depending on the laws where you are, you may not use them in anything but General Purpose applications. In the USA, you cannot use anything that isn't labeled as approved for hazardous environments in hazardous environments.

You can make the mistake of assuming that a transmitter which looks like an explosion safe transmitter is one, and you might be wrong. Many vendors use similar transmitter housings for both general purpose and hazardous area
classifications, especially if the unit is IS, and doesn't require a huge enclosure.

If you are using "used and refurbished instruments" you are taking the chance that you will be improperly using them. Make sure you get detailed documentation, including serial numbers, from your vendor. With a serial number and a model number, any vendor can tell you what the unit is rated for, and may even be able to provide you with the correct labeling for the device (probably for a fee).

But remember, sometimes you get what you pay for.

Walt Boyes
Editor in Chief, Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net

The certification label is a good place to start, relying on the serial number alone could be a bit dangerous. The manufacturer can only tell you what the instrument was at the time it was supplied, there is no guarantee that the previous owner hasn't modified it. If the certification label is missing then I wouldn't touch the instrument, you are leaving yourself open to problems the first time any competent external body does a site inspection.

Steve
MTL Instruments
www.mtlblog.com

Ahsan,

You need to be extremely careful when deciding to use "used and refurbished" equipment in an explosive atmosphere. Any such items need to be refurbished to the original standard if they are to be suitable for this application. The work involves the repairer having access to original design information, and repeating tests on reconditioned items to verify that they comply. A repairer will generally need some form of certification to demonstrate that they have the required capability. Possibly one of the reasons why your refurbished equipment has no labels is that it has not been refurbished or reconditioned to the required standard.

Bruce

If you have knowledge about enclosures used in industries then you can know whether transmitter is ex-proof or not. So enclosure of the transmitter or any instrument or any panel can tell you whether it is ex proof or not. And for I/S device you need to check supplies and all.

I do not have knowledge of enclosures. I need to have it. My primary question is the difference between explosion proof & intrinsically safe enclosures physically. Do you know any URL or any supplier giving this info?

Okay.

First, there is no such thing as an intrinsically safe enclosure.

Intrinsic safety is a function of circuit design.

There are three basic standards, currently, depending on where you are, for explosion proof enclosures.

The oldest, and the most commonly used in North America, is the NEMA standard, with Class and Division ratings. Next most common is the EU system, the Eex standard, and finally, the new ATEX standard. All of these standards will be combined soon into the forthcoming IEC Eex standard, which should then be utilized worldwide.

If you want intrinsically safe field devices, you need to order them that way from the vendor, or purchase intrisically safe barrier devices from companies like Pepperl + Fuchs or MTL/Cooper-Crouse-Hinds.

There are a dozen companies who make "explosion proof" enclosures. If you want to make a field device that is not rated intrinsically safe suitable for use in a hazardous location, you put it into a device enclosure that is rated for that service, AND YOU CORRECTLY WIRE IT UP USING CONDUIT AND WIRING PRACTICES THAT ARE DESIGNED AND RATED FOR THAT SERVICE.

And if you are going to use "explosion proof" enclosures, you need to have the operations and maintenance staff trained in their use and maintenance, too. Otherwise you'll get lots of instances of "the magic bolt."

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net