A second area for communication standards that has had significant impact on
industrial automation is digital fieldbus. Fieldbus is a digital communication network
for connecting intelligent plant devices into automation systems. Fisher-Rosemount
(Emerson) introduced a hybrid analog/digital fieldbus called HART (Highway Addressable Remote Transducer) that could communicate with devices and systemsfrom different suppliers. The digital communication component of the HART protocol
allows instrument information to be passed to a DCS to provide instrument health and
similar analyses, but the measurement value is still transmitted via an analog signal.
HART has been one of the most successful fieldbus implementations in industry.
A number of fully digital fieldbuses emerged following the success of HART. The
two most prevalent in the process industries are the Foundation Fieldbus standard
(controlled by the Fieldbus Foundation of Texas) and the Profibus standard (controlled
by the Profibus Trade Organization out of Germany). A resulting fieldbus standard,
Foundation Fieldbus, has become the primary standard for the industry. Standard
digital communications between automation systems and field devices have provided
a major step forward for automation systems architectures.
As human-machine interface (HMI) software and supervisory control and
data acquisition (SCADA) software hit the industrial marketplace, one of the chief
advantages of this software technology over other automation approaches was it
worked with most of the automation systems and intelligent devices then available.
This occurred through the inclusion of drivers (communication driver software)
developed for each system or device to integrate with the HMI/SCADA software
system. Wonderware developed an approach that capitalized on Microsoft’s Dynamic
Data Exchange (DDE) capability (which enabled communications between multiple
applications operating in a Windows environment) to produce NetDDE, a networked
version of DDE for the development of communication drivers.