what is the profibus and fieldbus in instrument?

Answer 1

These are digital communications systems linking factory-floor controls and instrumentation with computers. Both are of the family of "buses", and there are others such as Ethernet, RS-485, GPIB, and some vendor-specific buses. Each has an advantage, but the decision should be driven by what sort of controls and instrumentation you have on the factory floor, the data rates needed, the distances involved, and the electrical environment (EMI/EMC) you will need to deal with.