Losing Profibus nodes - S7-1500

Manglemender

Member
M
Join Date
Jul 2007
Location
Lancashire
Posts
1,289
I've encountered a strange problem today and thought I'd share to see if anyone else has seen it before.

We have a system on test that has a CPU1517F-3 PN/DP with most of the I/O on Profinet and about 20 nodes on profibus DP at 1.5Mbaud. The CPU is not heavily loaded and typical cycle times are around 1 milli-second.

Left alone, the system is stable and happy but once you go online to the CPU with TIA Portal V14 SP1 then nodes start to drop off the profibus for no apparent reason.

My initial thoughts were dodgy cabling but the cabling and connectors have been verified today as being A1 using an independent network testing tool from Softing.

The problem is very repeatable: laptop online = nodes drop off PB and PB nodes restart. Laptop offline = all OK again.

Has anyone else come across this problem or can offer an potential explanation?

Nick
 
@JRW

Thanks for the suggestion. The comms load is already set to 20%, we were considering increasing it to see if it made any difference.

My initial thoughts were that the network was on the edge and PG comms pushed it over the edge but the load on the CPU is so low that we really don't understand why we are seeing this issue.

I once put together a system with 60 drives on profibus and about 60 lots of remote i/o on profinet with no problems at all.

Nick
 
If your connection is profibus then:
Make sure your cables are all the same impedance, and preferably true Profibus cable, not just random RS-485 cable. Make sure your segment lengths are reasonable for the baud rate you're running. Drop the baud rate if you can; and if you can drop to 500 kbps even better. Check for proper termination. Make sure the terminated nodes are powered at all times.
 
There are at least 3 threads in a german plc forum about issues when going online with TIA on a 1500 CPU: Profibus faults even when PG is connected via Ethernet, and also CPU going into stop-mode.
As solution was mentioned to change the communication load, but there wasn't any feedback if this fixed the problem.

But you are not alone facing this problem.
 
Hello All,

The online connection is via Ethernet. The connection would normally be via a Scalence switch but we have also tested connecting directly to the CPU via the second Ethernet port and the result is the same.

The CPU is S71517F-3 PN/DP V2.0. I have another machine on test with a V1.8 CPU and have not seen the same issue but it is a much smaller network; I will take a much closer look at it next week as more nodes are connected to the profibus side of the CPU.

The comms load setting of the CPU is 20% so we may have to test the system with alternative settings to see the outcome.

It is good to know that others have experienced similar issues. All of the slaves on profibus are non-Siemens components but I don't know whether that makes any difference. I don't think we have a Siemens Profibus slave to try it with as almost everything now is profinet.

Nick
 
@JRW

OPC-UA may be enabled, I'm not sure, but The SCADA system is WinCC Professional and there is also a small HMI on the system. I'll try to get as copy of the project and check.

Nick

Update: The OPC-UA server is not enabled.
 
Last edited:
I have tested a machine programmed with the same version of TIA Portal (14 + SP1) that has a V1.8 version of the CPU and it does not exhibit the same problem. The next step will be to insert a V2.0 CPU and re-test.

Nick
 
The machine with the issues has a S7-1517F-3 PN/DP V2.0 CPU but it is currently in pieces so cannot be worked on at this time hence continuing the investigations on another machine.

@JRW Can you update the firmware in a S7-1500 CPU?

I've heard a rumour that others have been advised to use TIA Portal V15 but I can't yet confirm that or if it worked.

Nick
 
Yes. You can update
Go to online diagnostics >functions >plc>firmware loader
I’m told you can update to 2.5 even if you are using v14 sp1
 

Similar Topics

T
Powerflex 700 Losing Ready Status at the beginning of shift.
I've got a Powerflex 700 that doesn't like to get going in the mornings. This motor will run anywhere from 30 seconds to 5 minutes before it just...
Replies
1
Views
19
DarrylR
D
M
RSlogix 5000 force closing
Hello all, I have a question in regards to RSlogix 5000. I am having issues with the program force closing when I try to make online edits. We...
Replies
0
Views
114
Mangotango2018
M
M
Losing PLC Persistent data values
I am working with beckhoff plc in twincat 3 environment. I have a array of struct which I want to make persistent. I declared it with...
Replies
0
Views
102
maximusPrime11
M
P
Factory Talk SE quad monitor closing the wrong header screen when navigating screens
We have a quad monitor setup with FT SE and we are utilizing a header screen at the top of every display. when we open a new page we abort the...
Replies
0
Views
88
Pjohnny17
P
T
S7-1515-2 Output card losing output voltage
I have a Siemens 1515 controller with the configuration of cards (input, output, safety input, safety input, safety output). I am having an issue...
Replies
2
Views
173
Tadicus
T
Back
Top Bottom