Information Technology Reference
In-Depth Information
Sales
Serial
links
4-20mA
analogue
Fieldbus
3-15 PSI
Time
1930
1960
1990
Figure 19.2
Changes in the market for instrumentation parameter transmissions
There are three main categories for Fieldbus installations, these are Fieldbus standard, Other
domain standards and non-Fieldbus. The main Fieldbus standard are WorldFIP (standard in
France), Profibus (standard in Germany) and P-Net (standard in Denmark), and are all part of
the CENELEC European standard EN 50170. WorldFIP has the advantage over the others in
that it uses the IEC physical layer (the IEC 1158-2). The Fieldbus Foundation is an initiative
of mainly USA-based vendors. Its main aim is to standardise Fieldbus for the petrochemi-
cal/chemical industries. One of its aims is not to replace traditional DCSs (distributed control
systems), but to integrate with them. The main standards for Fieldbus products are:
•
Fieldbus Foundation - this was formed 1994 have defined low speed 31.25 kbps trans-
mission (H1). The H2 standard (which is equivalent to WorldFIP) will operate at 1Mbps.
•
WorldFIP (or WorldFIP Europe) - this standard has been incorporated into many prod-
ucts and supports a 1 Mbps transmission rate. WorldFIP contributes to the Fieldbus
Foundation, in their standardisation process.
•
Profibus - this has three main types: FMS (flexible manufacturing systems), DP (distrib-
uted peripherals) and PA (process automation). FMS and DP use RS-485 signalling,
whereas PA uses the IEC physical layer at low speeds. FMS and DP are part of
EN50170.
Other busses, such as the CAN bus, use only the lower layers of functionality, especially for
remote I/O.
19.2.1 BITBUS
Intel introduced the BITBUS for remote I/O capability to multibus systems. It allows pro-
grams to be downloaded and executed in a remote node for truly distributed system configu-
rations. Its outline specification is
Speed 375 kbps
Maximum nodes with/without repeaters 250/32
Maximum distance with/without repeaters
13.2 km max/1.2 km max
Arbitration
master/slave
