Siemens Welding System ST PCS 7 Manual De Usuario

PROFIBUS PA

Siemens ST PCS 7 · November 2007

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Direct interfacing of the devices in the field, especially in the 

hazardous area, together with the information content of the 

communication, are of significant importance in the process in-

dustry. PROFIBUS PA, which permits both digital data transmis-

sion and the power supply on a two-wire line with the intrinsi-

cally-safe MBP transmission technology (Manchester Coded; 

Bus Powered) is tailored to these requirements. It is optimally 

suitable for direct integration of the pneumatic actuators, sole-

noid valves and sensors positioned in operating environments 

up to Ex zone 1 or 0 into the process control system. 
The typical response time of a transmitter of approx. 10 ms indi-

cates that short cycle times can be achieved with the 

PROFIBUS PA even in the case of a segment configuration with 

up to 31 devices. Practically all typical applications of the pro-

cess industry can be implemented - both with small or large 

plant distances. Bidirectional communication and high informa-

tion content allow enhanced diagnostics for fast and exact fault 

detection and elimination. The standardized communications 

services guarantee interoperability and replaceability between 

multi-vendor field devices and remote parameterization of the 

field devices during operation. 
The PROFIsafe profile allows seamless integration of safety 

communication into the PROFIBUS PA. You need not configure 

a separate safety bus for your safety-related applications. The 

PROFIBUS PA with the PROFIsafe profile is incorporated in 

"Safety Integrated for Process Automation". This comprehensive 

range of products and services from Siemens for failsafe, fault-

tolerant applications in the process industry offers you attractive 

and cost-effective alternatives to separate safety systems.

You can define the degree of redundancy separately for the con-

troller, fieldbus and I/O levels of your plant depending on the au-

tomation task and the derived safety requirements, and match 

them to the field instrumentation (Flexible Modular Redundancy, 

FMR). You can find an overview of the redundant architectures 

of PROFIBUS PA under "Design".
The PROFIBUS PA is based on electrical transmission compo-

nents. A shielded two-wire cable is used for digital data trans-

mission and for the power supply. With line, tree and ring topol-

ogies, it is possible to configure networks with spur lines up to 

120 m and bus segments up to approx. 1.9 km for operating en-

vironments up to Ex zone 2. With bus segments for hazardous 

areas in line with zone 1, the max. possible length per spur line 

is reduced to 30 m and per bus segment to 1 km. The line 

lengths actually achievable in practice depend on the number of 

PA devices and their current consumption. Bus segments are 

terminated either automatically (with active field distributors AFD 

in the case of ring topologies) or with the passive terminating el-

ement for PROFIBUS PA (SpliTConnect terminator). 
The DP/PA Link is preferred for the gateway from PROFIBUS PA 

to PROFIBUS DP. When using the DP/PA Link, the transmission 

rate on the PROFIBUS DP is independent of the subordinate 

PROFIBUS PA segments. The configuration of the DP/PA Link 

depends on the operating environment (Ex zone) or the selected 

redundancy architecture. The types of coupler described in the 

Section "Gateways - DP/PA link and DP/PA coupler" are used for 

the configuration. With a small amount of data (small quantity 

framework) and low timing requirements, the DP/PA coupler can 

also be operated in stand-alone mode as a gateway. 

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Advantages provided by distributed field automation with appli-

cation of the PROFIBUS PA profile included low hardware over-

head, cost-effective engineering, increased operational safety 

and problem-free maintenance. These advantages are under-

lined by the following features:
• Modularity and uniformity from the sensor up to the control 

level permit new plant concepts

• Implementation of intrinsically-safe applications through use 

of the fieldbus in hazardous areas 

• Flexible Modular Redundancy (FMR) from the automation sys-

tem (controller) down to the PROFIBUS PA field device with re-

dundant architectures for environments up to Ex zone 2 (ring 

and line topologies with coupler redundancy) 

• Safety-related and fault-tolerant applications with low device 

and cabling overheads 

• Reduced configuration costs through simple, central engi-

neering of the field devices (PROFIBUS PA and HART with 

SIMATIC PDM, also cross-vendor)

• Simple installation using two wire cable for common power 

supply and data transmission

• Reduced commissioning costs through simplified loop check
• Low servicing costs thanks to simple wiring and comprehen-

sive diagnostics facilities

© Siemens AG 2007