PROFIBUS originated
in the European market and has become a worldwide standard
because of its performance attributes. PROFIBUS consists of
several variations which are designed for use in special
applications. The two PROFIBUS versions most commonly used are
PROFIBUS-DP (Distributed Peripherals) and PROFIBUS-PA (Process
Automation).
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.
PROFIBUS-DP
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-DP Features
-
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 Specifications
|
Physical Layer
|
RS-485 |
|
|
|
Cabling |
One shielded
twisted pair for signal and one pair for 24 VDC supply |
|
|
|
Topology |
Trunk with
drops |
|
|
| Cable
Length |
| Baud Rate (Kbits/sec) |
| Length |
|
| |
|
|
|
|
| 93.75 |
187.5 |
500 |
1,500 |
12,000 |
| 1,200 |
1,000 |
400 |
200 |
100 |
|
|
|
|
Number of Devices |
32 per segment; Up to 126
with 4 repeaters |
|
|
|
Bus Power |
Must have auxiliary 24VDC
supply |
|
|
|
Transmission Rate |
9.6K to 12M bits/second |
|
|
|
Data Access |
Token sharing for
multi-masters; peer-to-peer; multicast and cyclic polling for data
transfer; acyclic for asset management |
|
|
|
Data Transfer Size |
Up to 246 Bytes of Input &
246 Bytes of Output Depending on Device Type |
|
|
|
Device Identity |
Specific ID Number for each
device |
|
|
|
Error
Detection |
HD4 CRC (Cyclic Redundancy
Check) |
|
|
|
Support Organization |
PROFIBUS Users Group (www.profibus.com) |
|
|
PROFIBUS-PA
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 below. 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.
PROFIBUS-PA
Specifications
(different than DP)
|
Physical Layer
|
IEC
61158-2 |
|
|
|
Cabling |
Shielded
Twisted Pair |
|
|
| Cable
Length |
1900m (6200
ft.) |
|
|
|
Topology |
Trunk with
Branching |
|
|
|
Number of
Devices |
32 (Practical
limit of 0.50Amp divided by current used/device) |
|
|
|
Bus Power |
Up to 0.5 A
per segment |
|
|
|
Transmission
Rate |
31.25 Kbits/second |
|
|
|
Support
Organization |
PROFIBUS Users
Group (www.profibus.com) |
|
|
 |
