NORD Drivesystems BU0220 - Manual (Page 76)

PROFIBUS DP – Supplementary manualfor NORD Frequency Inverter SK 2xxE
76 Subject to technical amendments BU 0220 GB-0912
8 Additional information
8.1 Bus Configuration
In an industrial environment the correct installation of the Bus system is particularly
important in order to reduce potential interference. The following points are designed to
help prevent interference and problems right from the start. The installation guidelines are
not complete and applicable safety and accident prevention guidelines must be complied
with.
8.1.1 Laying the PROFIBUS DP cable
A bus segment consists of a maximum of 32 participants. Several segments can be connected together by
means of repeaters. In this way, up to 126 participants can participate in reference data traffic. It should be
noted that the reaction time increases as the number of participants increases.
The data transfer physics of the serial bus system by means of twisted two-wire cable (with
connected shielding) is defined in the specification of the interference-proof RS485 interface.
For applications with potentially high electromagnetic interference (EMC) and for long
distances, optic fiber cable should be used as the cable medium and fiber optic couplers
should be used for connection.
8.1.2 Cable material
The frequency inverter is usually connected to the PROFIBUS DP system by a twisted, shielded two-wire
cable. In EN 50 170, this bus cable is specified as cable type A. The guaranteed transfer speeds or transfer
distances can only be achieved without errors if the specific cable parameters are complied with.
With these cable types, the following extensions in length result:
Transfer rate
Baud rate [kBit/s]
9.6 19.2 45.45 93.75 187.5 500 1500 3000 6000 12000
Cable length [m]
Cable type A
1200 1200 1200 1200 1000 400 200 100 100 100
These cable length details are defined for a bus segment with 32 participants.
It must be noted that

the maximum cable length determines the transfer rate and vice versa,

the transfer rate is set identically for all masters connected to the bus,

the slaves support the set baud rate (see GSD file).
The standard PROFIBUS DP cable must comply with the following cable specifications:
Parameter Value
Number of wires 2 (twisted)
Impedance 150 Ω (3 to 20 MHz)
Capacitance < 30pF/m
Loop resistance < 110 Ω/km
Cable cross section > 0.32 mm²