One disadvantage of the FF is that a failure of the bus, such as a broken wire, can
shut down the entire process, whereas with the direct connection method, only one
sensor is disabled. This disadvantage can be overcome by the use of a redundant or a
backup bus in parallel to the first bus, so that if one bus malfunctions, then the
backup bus can be used [8].
A comparison of the characteristics of the serial data buses is given in Table
15.1. The original Foundation Fieldbus was designated H1. A new generation of the
H1 is the HSE, which will use an Ethernet LAN bus to provide operation under the
TCP/IP protocol used for the internet. The advantages are increased speed, unlimited
addresses, and standardization [9].
266 Signal Conditioning and Transmission
Termination Processor Termination
Smart
sensor
Smart
Twisted pair actuator
Smart
sensor
Power
supply
Figure 15.16