Siemens SIMATIC NET PROFIBUS manual Segments for a Transmission Rate of 1.5 Mbps

Configuring Networks

Length of the Tap Lines

If you do not attach the LAN cable directly to the bus connector (for example,when using a PROFIBUS bus terminal), you must take into account the maximum possible tap line length!

The following table shows the maximum permitted lengths of tap lines per bus segment:

Table 3-2 Lengths of the Tap Lines per Segment

Transmission

rate

Max. length of the tap lines per segment

Number of nodes with tap line

length of ...

			1.5 m or 1.6 m	3 m
9.6 – 93.75	Kbps	96 m	32	32
187.5	Kbps	75 m	32	25
500 Kbps		30 m	20	10

3.1.2Segments for a Transmission Rate of 1.5 Mbps

Transmission Rate 1.5 Mbps

The following maximum segment length can be implemented with the SIMATIC NET PROFIBUS LAN cable:

Table 3-3 Possible Segment Lengths

		Segment Length for Cable Type
Transmission Rate	– FC Standard Cable		– FC Trailing Cable
	– FC Robust Cable		– PROFIBUS Flexible Cable
in Kbps
	– FC FRNC Cable		– PROFIBUS Festoon Cable
	– FC Food Cable
	– FC Underground Cable
	– SIENOPYR–FR Marine Cable

1.500

200 m

200 m

Node Attachments at 1.5 Mbps

Each attachment of a node to the LAN cable represents a capacitive mismatch that has no effect at lower transmission rates. At a transmission rate of 1.5 Mbps, however, problems can arise due to these mismatches if the following guidelines in terms of type, number and distribution of node attachments are not adhered to.

3-4	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000