24/09/09 - Bihl+Wiedemann’s AS-i High Power Repeater: Just drown out external interference



Bihl+Wiedemann’s AS-i High Power Repeater:
Just drown out external interference


What is an AS-i High Power Repeater?

AS-i can be used in almost any environment. Still, occasionally it happens: In spite of a correct installation, interferences become so overpowering that standard AS-i cannot distinguish them from usable signals. To illustrate this, imagine the following: You want to talk to someone in a dance hall directly in front of a loudspeaker.
Bihl+Wiedemann now offers a solution: The AS-i High Power Repeater (BW 2384), that increases the usable signal in the critical field environment of the application and, thus, drowns out interferences.
Everything else remains the same: The simplicity, the interoperability, the safe recognition of remaining interferences/interrupts, the 2-wire technology, the usage in Safety at Work networks, etc.


How does a AS-i High Power Repeater work?

When employing AS-i High Power Repeaters, the critical field environment that is receptive to interferences is bridged by using increased transmission power between two AS-i High Power Repeaters. These Repeaters have a “standard AS-i side” and a “loud side” and are installed (at least) in reversed pairs (see figure.)

On their B-side, these Repeaters receive and send the standard AS-i signal from the Master or the slaves. On their A-side, that is facing the A-sides of other Repeaters, the Repeaters send and receive the same, however considerably amplified, “High Power Signal.” The properties of the signal and the encoding and thus all properties of AS-i remain the same.


Where can an AS-i High Power Repeater be used?

A typical location for AS-i High Power Repeaters are long sliding contacts (for warehousing applications with ASRS) where the symmetry of AS-i networks is destroyed due to several parallel AS-i network cables and other standard power supplies (for instance the 400 V VFDs lines.) In this case, interference from neighboring wires can be coupled into the AS-i network.
This can also happen if the AS-i network has to be hidden in a multi-conductor cable instead of using the common yellow cable.


Details:

Due to its high rate of symmetry, AS-i is protected against interferences as much as possible. If interferences occur and surpass a certain amplitude, the error detection process kicks in. It safely recognizes interferences and forces a repeat of the interrupted message. The situation becomes critical, if the symmetry is severely reduced and interferences are then more likely to occur on the network, or if external interferences “come through” due to overall asymmetries. In this case, the number of repetitions can interfere with the availability of the network.
These unusual constellations are solved by the AS-i High Power Repeaters: The critical network section of the application (for instance the sliding contacts or the multi-conductor cable) is installed between two AS-i High Power Repeaters. On its A-side, the first repeater sends a signal with a highly increased amplitude. Also on its A-side, the second repeater receives this signal as well as the inevitable interferences that are now minor compared with the usable signal, checks it for errors, and sends a regular error-free AS-i signal on its B-side. Therefore, the signal to noise ration between the two repeaters is increased, while keeping all remaining characteristics. The AS-i High Power Repeaters' B-sides, connected with the Master or the slaves, respectively, operate similar to a regular repeater.





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