Connect on a profibus network with field PG and complete shut down

Hi,

I just experienced something strange.
I connected a Field PG (PG/PC adress 0) on a profibus network to monitor something in the field. I connected the field PG with a standard Siemens MPI/DP cable. As a result the complete network went down or experienced a failure. The CPU remained in Run, but all safety went out because the profibus had a failure. This wa on a final line, so I caused a complete production stop.
When I did a monitor after I was connected, I could monitor, checked the hardware and everything was online. So by connecting I triggered a short profibus failure. In the diagnostic buffer all I can see is module I/O Access error.

So I disconnected my cable, restarted CPU and resetted all safety. Did all my changes at my office over ethernet after this issue.

Now the technical department sends me this:
We have a procedure to go online over profibus:
First of all we use a special cable with on one side a bigger connector that contains a opamp inside. We connect this cable first to the field PG and then to the network. With this special cable we don't generate profibus failers.

So I am now like ?????????

Owyeah: We have long cables and much repeaters, so yes it could be an unstable network.

I know that going online with a field pg on a weak profibus network is tricky and dangerous. But not on a stable profibus network. Why would you have repeaters and connectors with the abillity to connect ...

So my guess is that our technical department found a special way of going on the network... while the main problem is a weak network here...

About the cable with an opamp, anyone heard of such ?

Thanks for the replies,
Kind regards,
Gerry

You should be telling us how that cable is built...

Cable

They never let me see the cable.
It's only on a document noted that there is such cable.

cardosocea said:

You should be telling us how that cable is built...

Click to expand...

It's a bit of a wild guess, but I'd suggest that there might have been a termination resistor switched in on the programming cable. If you switch a terminating resistor into a profibus network, it won't look any further past that point for more profibus devices. So that would explain why all of the I/O dropped out.

Could be way off base, but that's the first place I'd look.

How did you have the PG interface configured? I can't remember which, but I seem to remember that one setting on another network could cause some damage. I think it was PG interface set as profibus and the MPI network, but can't say for sure.

I connected with a standard Siemens cable. So no terminating resistors in my cable. My settings were correct, because I could monitor right away. But making the physical connection caused a short failure for some reason. In my settings I had Only master on the bus ON... maybe that caused something ? I don't know...

Gerry
The cable you seek is called a multi tap or tap line cable for a PG
https://mall.industry.siemens.com/mall/en/ww/Catalog/Product/6ES7901-4BD00-0XA0
Although this shows two plastic looking ends- mine has the metal straight type on one end

I had an issue once where I connected a grounded stationed PC with a CP card, into the plc network Profibus line, and the CP card shorted as soon as I plugged in the cable. I never spoke to me again.

If the PG was grounded through a charger cable on 230 volt, maybe the Profibus network/plc card, had a hickup because of different voltage levels due to the grounding...

I don't get this

Hi,

I really don't understand this. I mean, don't we all use profibus connectors with the possibillity to connect or PG with a normal RS485 cable form Siemens, don't we all us the sub D connection on repeaters to connect our laptops.

I never have been tol to use thes special cable from Siemens...

Maybe it's a cable that does the connection with a galvanic split, but still... this is the first time in 17 years that I may not connect the regular way ?

Kind regards
G

JRW said:

Gerry
The cable you seek is called a multi tap or tap line cable for a PG
https://mall.industry.siemens.com/mall/en/ww/Catalog/Product/6ES7901-4BD00-0XA0
Although this shows two plastic looking ends- mine has the metal straight type on one end

Click to expand...

The cable has been around a long time..
I know you have been taught that a profibus "spur" line is bad...? Of course you have
Especially at 12meg
You've been lucky all these years and probably only connecting to 1.5meg networks

So when hooking up your PG- this prevents this or helps a lot - nothing in life is 100%

Combo said:

I connected with a standard Siemens cable. So no terminating resistors in my cable. My settings were correct, because I could monitor right away. But making the physical connection caused a short failure for some reason. In my settings I had Only master on the bus ON... maybe that caused something ? I don't know...

Click to expand...

I don't know the real answer, but as you said you used the standard "MPI" cable and our experience is, that doesn't work - piggy-backing it on a DP connector puts down the network...
What does work is a standard DP cable with DP connectors, with the terminating resistor at the PG side to "on" and the one that goes piggy-back to "off"

Combo you really havent provided any useful information as to give us a possibility to guess at the reason why you cannot connect with a normal cable.
Please inform us about the details of this Profibus network.
And get some details about the special cable. It does sound as if it as a cable with an integrated isolation/repeater so that a spur is avaoided. Manufacturer and type, or is it home-made ?

Apart from that I once saw a FAQ from Siemens describing how to calculate the degradation of the signal based on the cable lengths, number of stations, tabs, connctors etc. The 32 limit per segment is really not a hard value. The actual possible bumber of stations in a segment may be more, or it may be less.

It can be a grounding issue as orense suggest.
It can be a termination issue.

You could also get a profibus analyser to get to know what is really going on with this network, rather than guessing.

Oh yeah.

Profibus networks are iffy. They may work fine and thay may fail, and to find the cause is not easy.
Best advice, always keep Profibus networks small and simple. Dont setup complicated networks.
For the reason that with many stations and transitions failures becomes more probable, more difficult to pinpoint, and have greater negative consequences since more stations are affected. (That is bad x bad x bad = extremely bad).

If one has a complicated profibus network, that is also important for production (probably it is, why else have the profibus network), then one should have a permanently installed profibus analyser.

About the cable with an opamp, anyone heard of such ?

Click to expand...

Can you take a picture of it?

Look at post 7