Connect 120 nodes (IMCC) via single profibus master

Dear Sir, 

I want to connect 120 nodes(IMCC) via single profibus master. 

I planned to use 3 RLM(Redundancy Link module) and 40 nodes in each RLM.

Is it possible? I have read that maximum 32 nodes per segment. Can it be increased by using repeaters.

I have attached my proposal. 

I want to use 1.5 MBPS.  

Kindly suggest.

Surendhar M

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Split from making 300 node profibus.

Hello Surendhar;

Answers to such questons on a non-Siemens equipment must be answered by the manufacturer of this prodiuct, in this case ABB.

https://new.abb.com/control-systems/system-800xa/800xa-dcs/fieldbus-protocols/profibus/profibus-redundancy-link-module-rlm01

From the attachment below, you can see that a segment on a RLM01 consists of a master and 31 slaves; with a repeater you can add a segment to communicate with more "Profibus clients", so in principle you should have no problem going to 40 nodes with one repeater (note that each repeater must also be counted as a node on Profibus, so a segment can only care for 31 nodes).

Take care also of the length of each segment. At 1,5 MB network bus speed, the length of a segment is limited to 200 m. With a repeater you can double that to 400 m. If the total length of a network attached to a RLM01 is longer than that, either you need a second repeater to maintain the bus speed, or you must lower the bus speed (to 500 kB for example, for a distance of 400 m/segment)..

Hope this helps,

Daniel Chartier

Thank you sir.

I hope the same is applicable to Siemens by using Y Links.

Surendhar M

Hello Surendhar;

I am not completely familiar with the RLM01, so I cannot discuss the inherent limitations of these modules without further study or assistance from ABB (which I suggest you consult for this type of network design).

I know the Y-links though, and can discuss the limitations they would impose on your project.

SIMATIC Bus links DP/PA coupler, active field distributors, DP/PA Link and Y Link

https://support.industry.siemens.com/cs/ww/en/view/1142696

As you can see from the technical specs of the Y-Coupler (one element of the Y-Link) below, you are allowed to have up to 64 slaves on a Y-Link, using repeaters (OLMs are acceptable to, for fiber-optic connection).So far it looks good for your design.

However, the Y-Link is considered by the redundant CPU masters (H-system) as a single Profibus-DP slave, and as such follows the limitations of a single Profibus slave: the amount of data to be exchanged with all of the configured underlying slaves on the Y-Link is limited to 244 bytes OUT/244 bytes IN, no matter how many underlying slaves it connects to the redundant masters. So each of your 40 slaves on a Y-link (with repeater to control more than 32 nodes) would each be limited to 6 bytes OUT/6 bytes IN on average, on each Profibus cycle. Is that enough for your project? 

Another limitation is the 244 byte parameter assignment frame for the slave, less known but that can cause problems when you have so many underlying slaves. There is no warning that you are approaching this limit, only that you have overpassed it and that the slaves cannot be configured when you do.

So be very careful before actually committing to using Y-Links on the project, and I would carefully evaluate any other type of link from other vendors. You could also get help from a Siemens rep, or come back to the forum when you have advanced your network design

Hope this helps,

Daniel Chartier