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Topic Title: Backward Engineering of Communications
Topic Summary: Can I work out the comms (RS485,RS422 or other)
Created On: 13 January 2010 10:12 PM
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 13 January 2010 10:12 PM
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Avatar for romanpk.
romanpk

Posts: 3
Joined: 12 July 2008

Hi all

I have a challenge ahead to try and backward engineer a system the incorporates a 2 wire (busbar) commnications network.

System overview:

Hanging monorail system aroun 1999 that transports pallets around a large loop. The system is controlled by a Siemens S7 PLC which communicates over Interbus to units known as Block Section Controllers (BSC). These BSC's are a microcontroller that connects up to 16 sections of rail over a two pole busbar system. A section could have more than a single carrier on it so would suggest multi drop.

Information is very limited but in essence the carrier reports its ID (each is individually numbered) at each section back to the the BSC. This is passed back to the PLC. The PLC can ask the carrier to load a pallet, offload an existing pallet or move to the next section. I have some details of the communications passed back and forth and would be easy to work through once connectivity is acheived.

The the units on the carriers are now obsolete and the original design information has been lost through business changes over the years.

Ideally we would look to upgrade to wireless with direct connectivity to the PLC. But this is not an option at present and as an interim I would like to upgrade the carrier control with a PLC or similar controller but need to work out the comms type between the carrier and the BSC.

So to the question.

The communications is over two busbar poles + Data & - Data and is +/- 30v DC.

I have a spare BSC and have a scope on the output, does anyone know how I can figure out or carry out tests to try and determine what the comms might be or if a device exists that could aide in this.

Any information geatly appreciated.
 14 January 2010 02:42 PM
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westonpa

Posts: 1771
Joined: 10 October 2007

You can use a data sniffer / protocol analyser and these can be purchased......search Google to see what is available at a cost you are prepared to pay.

However first I suggest to get any details off any of the kit which is doing the communicating and do a Google search. Information for much obsolete equipment still exists on the internet and then you maybe able to either find someone who once worked on it or alternatively details which allow you to identify the protocol, etc.

Regards.
 14 January 2010 03:23 PM
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Avatar for romanpk.
romanpk

Posts: 3
Joined: 12 July 2008

Thanks for the reply

It is a bespoke piece of kit made by our own company in Germany and this part of the business no longer exists so all knowledge has also dispersed. I did try old faithful (Google) and have also taken many of the component ID's and Googled them as well but nothing has stood out.

Off to Google again to look at sniffers.
 14 January 2010 10:39 PM
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westonpa

Posts: 1771
Joined: 10 October 2007

When I worked for Mannessman/Siemens we used RS485 from a PC/PLC comms card to a converter for RS232C tx/rx via the busrail. The bus rail was zoned and thus we used a serial line, converter, etc., for each zone which was isolated from the others by a plastic isolating piece in the busrail.

Regards.
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