Pepperl+Fuchs Blog

How to Use an AS-Interface Repeater

Posted by Tim Cicerchi on Fri, Sep 13, 2013

It is quite well known that AS-Interface has a 100 m limit per segment.  Did you know that you can use a repeater to get longer lengths?  Unlike other industrial networks such as PROFIBUS or DeviceNet where repeaters are rarely used, on AS-Interface repeaters are used all the time.  When running a repeater, take some care in how everything is wired.

AS-Interface Repeater


Watch how you connect the terminals.  On the panel mount repeater, you have terminals on the top of the module, bottom of the module, and then adjacent to each other.  The terminals adjacent to each other are just internally jumpered.  There is no repeating done here.  They are just duplicate terminals for landing maybe a trunk line and a power supply.  So to repeat the AS-Interface signal, you must land one segment on the top and the second segment on the bottom of the repeater.


The repeater is a galvanic isolator and only repeats the AS-Interface signal.  A separate power supply is required for each AS-Interface segment before and after the repeater.  You can never use one power supply to power up both sides of the repeater and you can never use more than one power supply to power each segment.  AS-Interface requires exactly one power supply per segment.


The LEDs on the repeater are for POWER and FAULT.  The POWER LED tells you if you have power on that side of the segment.  If you don’t have this LED lit up, then maybe you have to add the second power supply that we talked about.  The FAULT LED always throws people off.  This LED looks at communication on that side of the repeater.  If there is no AS-Interface module on that side of the repeater, the red FAULT LED will be on.  It will be on even if you have power.  Some people when they are setting up a repeater immediately call the factory when the see the FAULT LED, but the only reason it is there is because they haven’t wired the rest of the network yet.

Take a look at another one of our AS-Interface in a Hurry videos to see how it’s done.

Learn more about AS-Interface by listening to our weekly podcast series "TechTalk":

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Topics: AS-Interface

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