Flowserve MX/QX Profibus DP/PA Field Unit - Manual (Page 17)

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PB DPV1 / PA Field Unit Installation and Maintenance FCD LMENIM2336-03 – 12/12
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These distance rules (or limitations) are based on the physical characteristics of the RS-485 topology
and are not a limitation of the PROFIBUS protocol. If the distance required between two stations or
the total network distance is greater than allowed by the PROFIBUS specifications for copper cable, a
conversion to fiber-optic cable may be required. Figure 2.5 shows the baud rate versus copper cable
distance using PROFIBUS.
Table 2.1 provides the guidelines for maximum segment length versus baud rate.
Table 2.1 – Maximum Segment Length
Baud Rate 9600 to 187.5K 500K 1.5M
Maximum Segment Length (meters) 1,000 400 200
Table 2.2 provides the guidelines for maximum network length versus baud rate (assuming the use of
up to 9 repeaters).
Table 2.2 – Total Network Length (with up to nine repeaters)
Baud Rate 9600 to 187.5K 500K 1.5M
Total Network Length (meters) 10,000 4,000 2,000
NOTE: The maximum lengths are estimates and depend on the condition of the actual cable.
Tables 2.3 and 2.4 detail the various types of cable which can be used for network cabling. For
additional guidelines, see the following publications:
• PROFIBUS Networks SIMATIC NET 6GK1970-5CA20-0AA1.
• PROFIBUS Technical Guideline for PROFIBUS-DP/FMS, Version 1.0, September 1998; PROFIBUS
Guideline, Order No. 2.112.
There are different types of electrical data transfer cables:
• Standard bus cable.
• Standard bus cable with halogen-free sheath (type FRNC).
• Cable with PE sheath for use in the food and drug manufacturing industries.
• Direct buried cable with additional protective sheath for buried service.
• Trailing cable – This is a special cable type which is used where parts of the machine move
occasionally or continuously.
• Festooned cable – Comparable to a trailing cable, but has an additional strain relief element.
NOTE: Cable must meet the requirements as listed in table 2.3 to ensure reliable network
communications.
Table 2.3 – Recommended PROFIBUS DP Cable Parameters
Characteristic impedence at 3-20 MHz (ohms) 135-165
Operating capacitance (pF/m) < 30
Loop resistance (ohms/km) ≤ 110
Core diameter (mm) > 0.64
Core cross-section (mm 2 ) > 0.34