PROFIBUS PA network problem

in our plant we have a pa network when our fc drives is off we have not any problem

but when we turn on fc drives our data lost.

cos of this problem we forced to reduce devices on network .

now we have 3 dp/pa coupler and 5 profibus device on each subnet.

if we add just one more device data will be lost .

when we turn off fc drives we can add devices without problem to one dp/pa coupler.

is there any suggestion to solve this problem?

thank you

Hello 2rostkar;

The description you give of your situation might indicate a sensitivity to some form of interference (EMI, ground loops) from the drives or motors connected to them.

Could you please identify the drives you are using (make and model) and the gsd file used to integrate them to the Profibus network?

Also, what type of cable are you using for the Profibus-PA network, is it a certified Profibus-PA cable (from Siemens, Belden, Unitronics...). Do you use PA terminal blocks or Siemens Split-Connect technology to connect the spurlines to the PA trunckline? How are the lines terminated, and what distance do you cover per segment? All these physical elements may have a relation to your problem.

A diagram explaining your network setup might be helpful.

Hope this helps,

Daniel Chartier

hi dear dchartier

we use emotron FDU 2.0 drives in different sizes from 30 kw to 500 kw and their official gsd files

i dont know about cable certificate and we use split connect system and terminators didnot  use and

longest segment does not exceed from 50 meter

thanks for your help

Hello 2rostkar;

I am a bit confused.

Information I have found for the drives you mention states that Profibus-DPV1 is the only version of Profibus supported, not Profibus-PA. See the following links:

http://www.emotron.com/Documents/Documents/Products_Solutions/Products/AC_drives/Emotron_FDU/Emotron_option_Fieldbus_Instruction_Manual_01-3698-01r7_EN.pdf

The module supplied from CG Drives & Automation supports Profibus-DP (version 1).

The physical transmission medium of the bus is a twisted pair of cables (according to the RS-485 standard). Maximum length is 100-1200 metres (depending on the baudrate).

The same comment can be found in section 3.3 of this link:

http://www.elprodrive.cz/download/Manual%20FDU%202.0/VFX_FDU%202.0%20Option%20Fieldbus%202.0%20ENG%20r1.pdf

If you have other information, such as a Profibus-PA profile for these drives please attach it here so we can have a look at it.

Hope this helps,

Daniel Chartier

Dear daniel

we have two type of profibus network in our plant 

profibus dp for drives 

profibus pa for field sensors ( flow , pressure, ph , conductivity ....)

as i mentioned we dont have problem in profibus dp but in profibus pa network we have data lost when our fc drives is working so we lost our sensors data . 

We use dp/pa couplers for pa sensors 

thank you 

Hello 2rostkar;

Sorry I misunderstood your problem description earlier.

So, you have interference in your PA bus when the drives (or some of them) start up? And you have limitations on the number of PA instruments you can hook up to a DP/PA Coupler? Have you made sure that no Profibus cables are within 15 cm of the drive power cables?

Let's start by providing you with a brief but very comprehensive troubleshooting guide for PA Networks:

http://www.automation.siemens.com/w1/efiles/weighing/techn_publications/Profibus_en.pdf

There are other documents on installation, maintenance and troubleshooting of a PA network, much more detailed, from Profibus.com and Procentec that you can look for on the web.

Something in your installation is not correct if you have EMI problems. First thing to think about is proper termination of the PA bus. Using Siemens SplitConnect technology, you really should look into purchasing 2 of the following termination circuits to add at both ends of your PA bus: 6GK1905-0AE00

https://mall.industry.siemens.com/mall/en/WW/Catalog/Products/10009276

Then you should use the techniques shown in the article above to look for grounding and connection issues; EMI often is associated with ground loops, signals or harmonics coming back to the sensors through ground connections. Please take the time to prepare investigations of your network, or bring in an experienced integrator who will be able to troubleshoot the bus.

Hope this helps,

Daniel Chartier

Hello daniel

do you suggest to buy profibus analyzer to investigate our network?

Hello 2rostkar;

Purchasing a Profibus analyzer is always a good idea if you have recurring installation and maintenance issues in your plant. There are many on the market, going from free software such as Siemens' Amprolyzer (required: purchase of a Profibus communication processor) to very expensive (but with full-blown diagnostics capacities) Profitrace oscilloscope from Procentec, with many tools (from Softing and Prosoft-Technologies, for example) at various prices and functionalities available on the market.

Learning to use the purchased analyzer properly and interpreting results correctly is as  important as having it in hand, and that requires training and experience. There is a learning curve that must be taken into account and you should not purchase the analyser without taking the training into account.

So, for one-shot problem solving, it is sometimes better (and cheaper) to have someone from outside come in to the plant with is knowledge and equipment to help out. But tht is a contract discussion you should have witht he maintenance managers at your plant.

The article I suggested earlier shows some tests you can do with a multimeter, to start diagnosing grounding and faulty termination issues. At least start with tools you have and understand well.

Also, consider this: a Profibus DP/PA coupler isolates the 2 buses form one another. DP uses RS-485 while PA uses MBP (Manchester Bus Powered: look this up in Profibus manuals), so signal levels and coding are very different. Normally you should have no transmission of signal directly from the DP side to the PA side. So why does starting a drive (actually the motor attached to the drive) cause disruption (loss of data transmission) on the PA side?

First, does this happen with any motor start, or can you evaluate if particular motors produce this effect? Try registering the time of data disruption on the pA bus and associating with specific operations on the DP network.

Second, examine your topology and cable runs very closely for those drives that are associated with a loss of PA data. Are there places where power cables are set too close to network cables? Can there be grounding issues on the drive or the motors that could interfere with the PA couplers?

Once you have done this preliminary examination of the network and if you still cannot find issues with the PA bus (remember to start by correcting the PA termination issues, as discussed in an earlier post), then you can feel the need for an analyser, and possibly an experienced integrator to help you out.

Hope this helps,

Daniel Chartier