Difference between fieldbus and group bus?

I ma new in fieldbus and wanted to learn about it, can anyone differentiate Fieldbus and group bus? I come across FCU (2160) of Emerson it has 6 port, 4 fieldbus and 2 Group bus, what the difference between the two and when does group bus usually use?

thank you,
page 54 onwards


Not being an expert on Emerson/Rosemount, all I can say is that it appears Groupbus is used to link Tank Radar Heads, either invidually [on RS232] or daisy chained [on RS485] back to a Field Control Unit as you have already indicated.

The terminology doesn't appear to be used anywhere else in industry. It wouldn't be the first time designers have made up a word / phrase to suit their application, to good effect.
Groupbus is a name for proprietary comm protocol.
From a quick reading it is not clear to me whether the term Fieldbus (upper case F) refers to Foundation Fieldbus, or whether Fieldbus is another proprietary fieldbus (lower case f).

There are lots of fieldbuses, because anyone can create a protocol and call it a fieldbus.
There is no global fieldbus police force to enforce a standard of terminology.

Recognized fieldbuses like Foundation Fieldbus or Profibus are run by an organization that has a certification process for devices that must be certified for the device to use the trademarked fieldbus name.