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What is the meaning of FISCO in Foundation Fieldbus? And what is the difference between it and NTT concept?

FISCO is Fieldbus Intrinsically Safe Concept. Another concept is FINICO concept. I have not heard about NTT. Most probably it will be 'Entity'. The entity is the older approach before FISCO and FINICO. Pl. check the website of fieldbus organisation http://www.fieldbus.org/, they have excellent education material free. Hope you will get all your answer.

Wow, clever catch on the 'NTT'

It is FNICO not FINICO. But it looks like the term FNICO is also going away.

Entity is traditional way of doing intrinsic safety created for those days when you connected one device to each barrier. It turned out to be impractical for bus designs because it provides too little power, severely restricts cable length (barriers had to be put in Exd boxes half-way into the field), and is very tedious to engineer in terms of compiling entity parameter data.

FISCO is also intrinsic safety, but much simplified, ideal for bus. It is the outcome of extensive lab testing. It provides more power so you can have more devices. It permits longer wires so you can reach all the way into the field. Engineering is lots simpler as you need not compile the entity parameters.

Another concept is called "field barrier". It is essentially a FISCO barrier mounted in the field, powered by an Exe trunk.

To learn more about fieldbus in hazardous areas take a look at chapter 3 of the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online: http://www.isa.org/fieldbuses

Cheers,
Jonas