Siemens SIMATIC NET PROFIBUS Instructions d'exploitation télécharger pdf (Page 19)

Network Topologies

3.3 Ring Topology

SIMATIC NET PROFIBUS Optical Link Module OLM V4.0

Operating Instructions, 01/2013, C79000-G8976-C270-03

3.3.2 Redundant Optical Ring with two OLMs

Setting up a redundant optical ring with two PROFIBUS OLMs can be seen as special case

of the redundant optical ring and can be implemented with the following two configurations.

* If OLM / P22 or OLM / G22 are used, an additional DTE or bus segment

can be connected to Ch 0.

How the LEDs react in the redundant optical ring:

A frame received by any channel is passed on to all other channels. If the frame was

received at an optical channel, it will also be sent back to the sender on the same channel as

an echo and therefore serves as a monitoring frame to test the fiber-optic links between the

OLMs.

The OLM recognizes whether a received frame is an echo or a frame that was forwarded. In

the case of an echo frame, the channel LED stays off whereas in the case of a forwarded

frame it will light up yellow. In networks with more than two OLMs, echo frames and

forwarded frames will alternate quickly. Due to the extended display-time of at least 300 ms,

all channel LEDs seem to be lit yellow continuously.

The channel LEDs may react differently in the redundant optical ring only if the following

conditions are met:

1. The redundant optical ring consists of exactly two OLMs and the two fiber-optic links are

of different length (difference > approx. 2 m).

Under these conditions, the receiving OLM will always receive a sent frame first on the

channel with the shorter fiber-optic link. The channel signals this with a lit yellow LED. The

frame on the other optical channel is interpreted as an “echo frame”, the channel LED stays

unlit. Since the fiber-optic cable lengths represent static variables, the display reaction is also

static.

Figure 3-4 Configuration 1 Figure 3-5 Configuration 2

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 63 64

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Siemens SIMATIC NET PROFIBUS Instructions d'exploitation Page 19