Need Siemens Profibus Help

I have a system using a S7-318DP. I have purchased a Diagnostic Repeater and placed in the network to try and gain insight to problems we have with the network. I am having two problems with using the repeater, which most likely are related.
1. I cannot seem to get a network topology from the unit. I am using Step7 V5.2 SP1, but the Prepare Line Diagnostics button remains grayed out.
2. The OEM of the equipment did a terrible job of routing the Profibus cables, a lot of wasted length. With the repeater there is DP1, DP2, DP3. Can I split up the existing into seperate segments DP2, DP3, and if I can; does each segment have a terminating resistor for a total of 3 instead of the present 2?

Any help is much appreciated.

Hi

I hate to say it but if you've already got problems with your network(s), adding a new device is probably not the right way to approach the solution.

Profibus is a very rugged resilient system, but does need to be installed correctly. Key issues which the Profibus Organisation (not Siemens) clearly defines in the installation guidelines include earthing, termination and suitable cable and screening. Every node on a copper Profibus network should be at an equal earth - 'equipotential bonding' as the guidelines have it. This is vital. Obviously a fibre-optic installation doesn't have this issue to contend with. Correct and accurate termination of network segments where appropriate is likewise essential. It's hard to say where these would be in your case since I don't know the layout of your cables. Are the cables themselves Profibus spec? There are requirements in the guidelines for ideal impedance, resistance etc.

Overall I would suggest stripping out as much as possible from the network including the Diagnostic Repeater. Get a multimeter and thoroughly check your installation. Get the Installation Guidelines as a download from http://www.profibus.com and use these as a stick to beat your OEM over the head with.

Good luck

Ken.

Ken,

The network is up and running and I have had the Siemens rep come in with test equipment. It was his recommendation to add the diagnostic repeater. The problems I was stating in my post are directed towards the installation of the diagnostic repeater itself.

The cables are all Siemens Profibus cables. If I can split up the segments with the diagnostic repeater, I may reroute some cables to shorten total line length.

The problems that we have experienced so far have been with a bad Y connector that is mounted on a piece of equipment that experiences shock loads. With the Y connector and the field terminated ends the two cables would just barely fit (streching the Y connector). When the shock load came the network would sometimes drop out for just a second. I have replaced the Y connector with a T connection and this appears to have solved that problem.

Thanks.

If anyone knows about the terminators, I could sure use some advice.

If anyone knows about the terminators, I could sure use some advice

Click to expand...

Whats the problem Glenn ?
Its really very simple: If a Profibus cable ends somewhere without another cable continuing at the other side of the connector - then there must be a terminating resistor.

The repeater looks a little special because up to four cables can be attached. Thats two cables on either side of the repeater barrier. The principle of termination applies to either side of the barrier.

For example: if you "end" both sides of the Profibus network on each side of the repeater barrier, then there must be a terminating resistor on both sides (one at each cable "end").

Thanks Jesper.

This is our first Profibus experience. I thought that it would need the terminators cut on, but I wanted some level of confidence before I shutdown a line that is currently running.

With the current system there are only 2 termination points, with the cabling changes and the diagnostic repeater this will now be 4 terminators DP1 (2 terminators), DP2 (1 terminator), DP3 (1 terminator)

Thanks again

Aha, now I see that the diagnostic repeater looks a bit different compared to the regular repeater.

There are two selector switches:
1: "terminator DP1" ON/OFF
If a cable isnt connected on both DP1 entries, then the switch must be ON.

2: "Segment DP3" ON/OFF
Not sure what this one does.
Also not sure why the other side of the repeater is called DP2 and DP3.
You have to read up on this in the manual to be sure that you dont goof up something