There are two flavors of PROFIBUS: PROFIBUS Decentralized Peripherals (DP) and Process Automation (PA)
PROFIBUS PA is used in process automation. The physical layer of PROFIBUS PA is Manchester Encoded Bus Powered (MBP), and the physical layer for PROFIBUS DP is RS-485. Even though a different physical layer is employed, PROFIBUS PA is the same protocol as PROFIBUS DP.
Process Automation environments, while typically requiring slower procedures, might also be characterized by explosive or hazardous environments. In such applications, PROFIBUS PA is a suitable solution. PROFIBUS PA can be deployed in hazardous environments since its physical layer: MBP, is intrinsically safe.
PROFIBUS PA Profile
The PROFIBUS PA profile is the basis for using PROFIBUS in process automation. This application is often characterized by intrinsically safe operation, large cable lengths, and device infeed via the bus cable. The PA profile defines the functions and parameters for process-control devices, such as transmitters, actuators, valves, and analyzers.
The profile specifies how the various services of the PROFIBUS communication protocol are used. Accordingly, for example, process data exchanged cyclically is based on a standard format for all devices. In addition to the measured value and/or manipulated measurement value, this format also features a status providing information about the quality of the value and possible limit violations.
PROFIBUS PA and DP
PROFIBUS PA enables long cable distances and explosion protection in process automation as well as the native, digital integration of field instrumentation in control systems and asset management systems. Based on the current state of the art, the connection is typically by means of a link or coupler via PROFIBUS DP.
The user benefits of PROFIBUS PA result from, among other things, the use of digital communication instead of analog communication, the suitability for easy proof of intrinsic safety type of protection, and the properties of the PA device profile oriented to the process industry.
PROFIBUS PA and PROFINET
It is also possible to implement PROFIBUS PA in PROFINET networks. The connection to PROFINET systems is by means of a “proxy”, which is a transition that acts as a master in the PA system but as a bus node (device) in the PROFINET system, which allows the PA segment to be easily configured in PROFINET. As a result, the proxy is integrated into the PROFINET infrastructure in the same way as the directly connected remote I/O stations, Motor Control Center (MCC), or PROFINET field devices.
For a complete overview of PROFIBUS DP and PA, take our free training: PROFIBUS Online Training Course.
