I am involved in a project which requires Profibus PA field devices.

I already know the basic guidelines of profibus PA network (cable length, maximum number of spurs, speed, etc.)

My questions here regards the large-scale profibus pa networks, that is, I have arround 200 field devices.

My idea is to connect my S7-300 PLC trough PROFIBUS DP to the DP/PA couplers. From each coupler my PROFIBUS PA segment/trunk will be chained trough junction boxes, and from each junction box the spur lines will connect to the devices.

With this general idea in mind, I am asking the following questions:

• Each PA segment/trunk  (up to 32 devices) shoud be connected to just one DP/PA coupler? That is if I have 200 devices, do i need to purchase 7 DP/PA couplers?
• Are the DP/PA coulpers rackable?
• As I am planning to use junction boxes, do they need to be purchased to a "big" brand like pepper-fluch (for instance) or can it be manufatured as an standard wiring junction box?
• Where can i find the cable specs for the profibus PA trunk and/or spur lines?

Thanks in advance!

soyxan

I am involved in a project which requires Profibus PA field devices.

With this general idea in mind, I am asking the following questions:

• Each PA segment/trunk  (up to 32 devices) shoud be connected to just one DP/PA coupler? That is if I have 200 devices, do i need to purchase 7 DP/PA couplers?
• Are the DP/PA coulpers rackable?
• As I am planning to use junction boxes, do they need to be purchased to a "big" brand like pepper-fluch (for instance) or can it be manufatured as an standard wiring junction box?
• Where can i find the cable specs for the profibus PA trunk and/or spur lines?

Thanks in advance!

Hello soysan;

Let's try to answer your questions:

• First, each coupler (non-intrinsically safe) can handle a maximum of 31 slaves. See the technical data of the coupler in the attachment, taken from this manual:

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

So for 200 PA slaves you will need 7 couplers (see the next point for further discussion)

•  You must use P/PA couplers as standalone slaves on the DP network, but then the whole Profibus-DP bus must be brought down to a speed of 45,45 kB, or if bus speed is important and you want to maintain the DP side at 12 MB for example, you must use a DP/PA link as a Profibus slave.

The DP/PA link is a  IM 153-2 Profibus-DP interface module with one or more FDC 157-0 attached to it, with a maximum number of 5 FDC 157-0 attached to a link. For 200 slaves you would then need 2 DP/PA links with a total of 7 couplers between the two links. This is where the FDC 157-0 is "rackable". But it cannot be placed on the main CPU rail, it must act as an independent slave on the Profibus-DP line, whether as a coupler or as a link.

The following FAQ can provide more answers:

How do you set up the DP/PA link and how do you configure the DP/PA link and DP/PA coupler?

https://support.industry.siemens.com/cs/ww/en/view/51678187

• In certain of our PA projects the client preferred junction box connections. After much research and comparison we decided to use Megablock hubs for PA and FF buses (both networks have the same physical specs) from MTL (recently purchased by Eaton); the most important points were integrated short-circuit protection (they call this SpurGuard) on every connection, which reassured the client (and the price of course was also important to the client...), and a variety of block sizes with available termination units that gave us a lot of flexibility in designing the network.

Hello soyxan;

As a late addition to my last post, here are the specs for Profibus-PA cable, Class A:

https://support.industry.siemens.com/cs/pd/169211?pdti=td&lc=en-WW

Hope this he;lps,

Daniel Chartier

New question published by FELIX_GUEZ is split to a separate thread with the subject Profibus PA - tool (software) to monitor the health of my intelligent instruments.

Best regards
CS Moderator