in reply to: Qustion posted by krish on 07 April 2006 at 05:55:23.
Keeping the analogue signal means you can continue using older instruments and controllers, with extra HART functions introduced when you want them.1200 bps was a good compromise between speed and reliability available in the mid-1980s, to work well on existing cables in industrial environments. HART FSK followed the well-known 1200 bps telecom practice Bell 202 (but with reduced signal levels).