Profibus-PA was developed to connect directly into Profibus-DP and may be used in intrinsically safe applications. DP uses the RS485 physical layer while PA uses the IEC 61158-2 physical layer designed primarily for process applications.
- High speed data access capable of handling time critical functions.
- Networks up to 32 devices (up to 126 with repeaters) on a 4-wire network; (2 wires for signal and 2 wires for power).
- Trunk network may extend up to 4,000 feet (1220 meters) per segment.
- Dramatically cuts wiring costs and commissioning over conventional applications.
- Interfaces readily into newer control systems.
- Used extensively throughout Europe with support in North America.
Profibus-DP is recognized as a high performance bus network capable of transmitting thousands of I/O point information in less than a few milliseconds. For that reason it has been used extensively for fast response control applications such as turbine servos and variable speed drives.
Profibus-PA was designed as a substitute for HART and 4 to 20mA signal transmission in the process industries. It uses function blocks designed around process industry requirements and uses the IEC 61158-2 physical layer, making it compatible with intrinsic safety circuits.
Profibus-PA links to the control architecture via Profibus-DP with a segment coupler or link as shown. Segment couplers are signal converters that adapt the RS-485 signals to the 61158-2 signal level. They are transparent from the bus protocol point of view. If segment couplers are used, the baud rate on the DP (RS-485) segment must be restricted to 45 Kbits/sec. The segment coupler also injects power into the PA network for the segment instrumentation.
Links are independent slaves on the DP network which represent all devices connected to the 61158-2 segment. When PA segments are connected using links there is no limit to the baud rate on the DP segment which enables faster overall bus network performance.