How do you choose between HART, Foundation Fieldbus, and PROFIBUS for a new installation?

Protocol selection criteria: HART - low cost for small systems, easy retrofit, maintains 4-20 mA compatibility, suitable when digital communication is secondary; Foundation Fieldbus - process industry focus, control in field reduces controller loading, best for large continuous processes with tight integration requirements; PROFIBUS PA - strong in European markets, similar benefits to FF, good for mixed discrete/process applications with PROFIBUS DP backbone. Selection factors: DCS native support, installed base (leverage existing expertise), application requirements (control in field need?), lifecycle cost analysis (wiring savings vs engineering), vendor support, and future extensibility. Consider wireless (WirelessHART, ISA100.11a) for monitoring applications.