Page 34 of catalogue Bus, identification and control systems of ifm Electronic GmbH

Controllers / Gateways, network extension

Controllers / Gateways, network extension

System description

Network extension · Introduction The classic AS-i bus is designed for a cable length of 100 metres. Experienced users have found out that often systems with 130 metres and more function without any problems. However, AS-i has a free topology so that there is no general installation rule for these 100 plus “x” metres. In many cases long , non-terminated cables cause reflections which overlay the AS-i messages and cause faults and message repetitions. There are several solutions for an extension by a further 100 metres: 1. The termination plug at the end of the long cable minimises reflections. In case of only few participants it should be connected at the end of the cable since the voltage drop there increases with the connected load. Another advantage of the bus termination is the improvement of the AS-i message quality for long cables and the use of Safety at Work components. 2. AS-Interface repeaters allow the cable length to be extended by a further 100 metres. The number of possible participants remains unchanged. Each repeater has a galvanic separation which divides the network into two segments. Each segment has its own voltage supply. The master segment can thus be supplied with voltage via AS-i power supply 1 and the segment after the repeater via AS-i power supply 2. This principle allows an increase in total current per AS-i network and improves the voltage drop. A repeater can also be used for safety reasons. A repeater is used to ensure that a short circuit on the secondary circuit has no influence on the primary circuit. AS-i networks can thus be divided into electrically separated segments. Each repeater has an internal propagation time which adds for series connection. This limits the number of repeaters to be used, see table below. 3. Dual masters in the centre of the machine allow an extension of the AS-i cable by a further 100 metres in opposite directions. Distances of 200 metres can thus be linked. One of the advantages is that twice the number of AS-i participants can be connected. Comparison of network extension methods There are different ways to extend the AS-i cable. The specified one hundred metres can be extended up to 600 metres in extreme cases. The following table shows the different possibilities and the different methods of cable extension.

Measure

Extension by

Additional power supply = more current from AS-i

Electrical separation

Voltage drop

Max. no. of slaves:

Cost / benefit* per slave (ranking)

Comment

Repeaters

100 m

yes

yes

uncritical

62

6.2 (4)

max. 2 repeaters in series and max. 1 repeater for Safety at Work master in the centre check total current from AS-i and message quality check total current from AS-i and message quality

Dual masters Termination plug Tuner

100 m 100 m

yes no

yes no

uncritical critical

124 62

2.8 (2) 0.95 (1)

100...150 m

no

no

critical

62

6.13 (3)

* Formula: (Unit cost / max. number of slaves)

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