Nestle Purnia Profibus Network Problems

Site: – Nestle Purina, Wisbech
Equipment: – Danfoss VLT2800 inverter network with Profibus
Reported Fault:-  Our customer Nestle Purina at the Wisbech factory was unable to speed up the profibus network without the drives dropping offline.

The Network has 3 servo drives, 10 – VLT2800 Drives and then an encoder at the end of line.

With our ProfiTrace  diagnostic hardware we were able to resolve the problem on the Profibus Network both quickly and effectively.
Picture below shows the network with all the danfoss drives switched off. Last node 22 is showing a very high reading.

On Terminator cable changed

We then found the end of line terminating resistor was not closed on the last node – Address 22 encoder. Once closed, node 22 went to a very low reading.

Immediatly after cable external - original cable from plc to node 1

To prove the PLC we connected a spare encoder from stores straight in the PLC on a separate cable. This was found to be ok.
We disconnected the profibus cable from the PLC and ran a new cable from PLC to the first node servo drive. This was not in the trunking, just laid across the bottom of the panel.

Closing the Terminating resistors on the encoder and replacing the cable between the PLC and the first node address, we then got acceptable levels on the Bar graph.
Below is the scope trace  with all the drives now on line.

Line 5 Scope Overall

Now that the network looked Ok with end of line termination closed and cable replaced, the network Baudrate can now be tried to set to a higher level.