Siemens SIMATIC NET PROFIBUS manual Configuring Electrical Networks, Profibus Networks, Parameters

Configuring Networks

3.1Configuring Electrical Networks

PROFIBUS Networks

PROFIBUS networks were specially designed for use in an industrial environment and one of their main features is their degree of immunity to electromagnetic interference resulting in high data integrity. To achieve this degree of immunity, certain guidelines must be adhered to when configuring electrical networks.

Parameters

The following parameters must be taken into account when planning an electrical network:

SThe transmission rate required for the task

(within a network, only one uniform transmission rate can be used)

SThe required number of nodes

SThe type of network components required (bus terminals, bus connectors, connecting cables)

SThe LAN cables to be used

SThe required segment lengths

SThe electromagnetic and mechanical environment of the cabling (for example surge voltage protection, cable route)

SThe number of RS-485 repeaters between any two DTEs is limited to a maximum of 9

SIncreasing the overall span of a network by using repeaters can lead to longer transmission times that may need to be taken into account when configuring the network (see Section 3.3).

Cable Termination

Regardless of the transmission rate, the ends of all segments must be terminated by activating the terminating resistor in the connector. After the terminating resistor has been activated, no further cable sections are permitted.

The terminating resistor is only effective when it is supplied with voltage. This means that the corresponding DTE or the RS-485 repeater must be supplied with power. As an alternative, the PROFIBUS terminator can be used as a permanent terminating resistor.

3-2	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000