Hi!!! I have a question about intrinsically safety barrier. Is an Intrinsically safety barrier (IS barrier) required for each instrument loop in hazardous area? In which case i.s. barrier is not required for instru. loop in haz. area? Thank you.

 

No. It depends on the hazardous area. If the instrument is located in Zone 0, yes, I.S barrier is required to limit the current flow.
If the instrument is in Zone 1 , it dependson the instruments. If the instrument electrical enclosure is Explosion proof type, you don't require the I.S barrier. In Zone 2, normally I.S barrier is not required, some other kind of protection to the instrument like EExd, EExn etc is provided. Again all depend on the type of protection available for a particular instrument. There are some instruments like some frlow swiches, densitometers, analysers etc where only instrinsically safe certified (EEx'ia')protectionn is available. In this case irrespective of the zone, I.S barrier is required. Hope you got some idea.

Regards,
Abdul Gafoor

 

Each loop must be barriered if it is Intrinsically Safe.

I suggest you talk to MTL or P&F who make these things and have expertise in the field.

 

there are other means of protection such as explosion proof,

Bob Peterson

 

Only case is that we use Eexd Instrument i. e explosion proof Instrument. But it is not preferred practice. if you do like this then any activity needs opening of Instrument enclosure can be done only after making area non hazardous.

Regards,
Shailesh C Patel
FDC - Control Systems And Instrumentation
Reliance Engineering Associates(P) Ltd.
Jamnagar Refinery Complex

 

Basically whenever a signal from Hazardous area enters to safe Area, it requires safety barrier.
It is applicable to visaversa applications. Intrinsic safety (IS) is based on the principle of restricting the electrical energy available in hazardousarea circuits such that any sparks or hot surfaces that may occur as a result of electrical faults are too weak to cause ignition. The useful power is about 1W, which is
sufficient for most modern instrumentation. IS is therefore inherently safe as evidenced by the fact that it is the only technique that is universally accepted for Zone 0 (high
risk) hazardous areas. It is also safe for personnel since the voltages are low and it allows field equipment to be maintained and calibrated ‘live’ without the need to
obtain a gas-free certificate. Finally, IS equipment is light in weight and can be interconnected by ordinary instrument cabling.

 

If you want the system to be intrinsically safe, then, yes, each instrument has to be on a barrier or isolator. This is not all there is to it though. Each instrument has to be rated for I.S. and you have to match the barrier or isolator to the instrument and it's cable. There is the capacitance (and to a lesser degree, inductance)of the instrument and the cable to be considered. The information for the instrument's capacitance and inductance should be found in the IS certification paperwork. I prefer galvanic isolators where feasible. They cost a little more but are much easier to wire in the safe area, (grounding).Talk to your MTL, Pepperl+Fuchs, R. Stahl rep. or find an engineer with some experience in intrisic safety. This is something that needs to be done correctly.