The original project was to read data from 6 off Eurotherm discrete controllers (model 32H8) on two identical WinCC SCADA workstations.
A problem occurred when the data was read back by the SCADA stations. One WinCC station read back all the instrument parameters from all 6 instruments. The second WinCC station could only read back the parameters from 2 of the instruments.
If the first SCADA was disconnected, the second rapidly acquired the missing data from all 6 instruments.
If the first SCADA was then reconnected, it would only read back data from 2 of the instruments.
The system was connected thus;
The system was re-organised to enable both the WinCC workstations to acquire the full set of data from all the instruments.
It was proven that the Lantronix XPress comms converter devices were only capable of handling 8 slave devices, or 8 instruments, in total.
The first WinCC station demanded data from the 6 instruments and received it all.
The second WinCC station also demanded data from the 6 instruments. To the comms converter, that brought the total demand up to 12 devices. It was only able to return 2 devices worth of data to the second SCADA station.
By splitting the instruments into 2 sets of 3, no Lantronix Xpress device gets a demand for more than 6 devices.
Similar problem with Moxa;
The Moxa equivalent of the Lantronix XPress converter has the same 8 slave limit, although 16 slave variations are available on request.
Eurotherm 32H8 dual loop controllers
Lantronix XPress Comms Converter 1
Lantronix XPress Comms Converter 2
Eurotherm 32H8 dual loop controllers
Lantronix XPress Comms Converter
Written by Steve Harris, Arun Control Systems.
Referencing work carried out by Colin Mitchell, DuPont Teijin Films, Dumfries
