We have a Profibus DP Network of 110 nodes
And we are using 485 repeaters for each segment (27 & 28 nodes) 6ES7 972-0AA01-0XA0
the topology used is:

CP342-5 - N1 - N2 - ... N27 - Repeat 1 (A1B1)
Repeat 1 (A2B2) - N28 - ... - N56 - Repeat 2 (A1B1)
Repeat 2 (A2B2) - N57 - ... - N83 - Repeat 3 (A1B1)
Repeat 3 (A2B2) - N84 - ... - N110

And we lose some nodes eventually, I just checked on the manual and am not sure about this topology, but well, am not the Profibus "expert". Could somebody help me please?

 

Hello RCroix;

At first glance, the topology you mention looks adequate. A repeater is required when a segment is full (30 nodes) or when a segment's length exceeds the permitted value at the current bus speed (100 m @ 12 MB, 400 m @ 500 kB, etc...). One easy way to check if a segment length is a problem is to decrease the overall speed of the bus; if the bus is stable at a lower data speed, then this could be your problem.

Also, you must check termination (at both ends) on the network. If you are using the terminator on the bus connectors (or on the connection points of the nodes, such as drives or MCCs), then you must make sure that the end-points (that are terminatd) are always powered up; the terminators require power to work properly. If you lose power occasionnally (shutdown for maintenance for example) on the end nodes, then your terminators are no longer powered-up, reflections appear on the bus and strange things can (will) happen to the bus, depending on the overall topology (loss of the master, loss of the HMI, loss of some nodes...).

Hope this helps,
Daniel Chartier

 

The arrangement you describe should be alright as no segment has no more than 32 nodes but there are other factors to be considered. Bus parameters,
cable lengths, termination practices, cable types, cable pull practices, cable locations, etc. all can affect the communications.

 

Daniel,

Well my problem was the length between the nodes, too short according to "Simatic Net - Profibus Networks" manual.

I already tested on 500kbps and it is working, but now we are rewiring the interconection for try 1.5.

Thanks a lot.

RCroix

 

RCroix,

Where in that manual did you find this information? I have been told for years about the minimum 1 meter distance between nodes but have never seen it documented.

Thank you,

David Adams
Application Engineer
CONTROL PRODUCTS
[email protected]
334-567-2017 office
334-567-8614 fax
334-303-9499 cell

 

David,

Check Chapter 3.

Do the math and you will see...

Best regards,

RCroix

 

Hello RCroix;
You will find this minimum value stipulated here, in the "Profibus Cabling Guidelines", by the Profibus Interface Center, Johnson City, TN, revision 0.4, page 7:

C. Special requirements for baudrates >1.5 MBaud
Use of baudrates greater than 1.5 MBaud requires special connectors. The connector must have built in Inductors in order to run with higher baudrates.

Spur lines are not allowed when using baud rates greater than 1.5 MBaud.
The maximum length between segments at 12 MBaud when using copper cable is:
100m / 327feet.
The maximum length between optical link components is:
300m / 981feet
In some applications, several bus connectors are used at electrically short distances. A minimum cable length between two stations of 1m/ 3feet is recommended.

Regards,
Daniel Chartier