Profibus is one of the advanced communications used in the process plants usually in cement and pulp and paper plants. The Profibus cabling provides high speed communications for field devices to provide data online 24 X 7 to control systems like PLCs or DCS.
Profibus comes in two stages or basically are of two types:
1. Profibus DP (Decentralised Periphery)
2. Profibus PA (Process/Plant Automation)
The Profibus PA is the main communication protocol which communicates from the field device and instruments to the central station or cluster. The Profibus PA works on the principle of Manchester Bus Powered Philosophy. More about it can be known here. The speed of transmission in Profibus PA is 31.25 kilo bits per second.
PA can supply power over the bus (2-wire communication) for devices such as transmitters and positioners which can be extended into non-habitable environments also. All PA transmitters are connected to PA segments or clusters which then pole the data from each transmitter and send it to Profibus masters or Linking Devices.
The Profibus DP on the other hand, is high speed transmissions used in between the controllers or DCS and the clusters. These transmit data at faster speed of upto 12Mbits per second. DP is used to collect data from various PA clusters at the same time.
The Profibus DP can provide cabling redundancy by cross cabling between two profibus master cards. The Profibus DP redundancy is achieved using the Profibus connectors or terminators which loops or terminates the Profibus DP at each cluster from the Profibus master to the last cluster.
FOUNDATION Fieldbus instrumentation
FOUNDATION Fieldbus is a standard for digital field instrumentation enabling field instruments to not only communicate with each other digitally, but also to execute all continuous control algorithms (such as PID, ratio control, cascade control, feedforward control, etc.) traditionally implemented in dedicated control devices. In essence, FOUNDATION Fieldbus extends the general concept of a distributed control system (DCS) all the way to the field devices themselves. In this way, FOUNDATION Fieldbus sets itself apart as more than just another digital communication “bus” for industry – it truly represents a new way to implement measurement and control systems.
This particular industrial network standard was first proposed as a concept in 1984, and officially standardized by the Fieldbus Foundation (the organization overseeing all FF standards and validation) in 1996. To date, adoption of FF has been somewhat slow, mostly limited to new construction projects. One of the “selling points” of FF is decreased installation time, which makes it a more attractive technology for brand-new installations than for retrofit projects.