I am building an application using the Siemens S7 PLC and the West Instruments MLC 9000 temperature controller. The system is controlled by LabVIEW on a PC with an OPC server, over RS232. I would like to know whether I would do better to control the MLC 9000 from the PC via the PLC over profibus or go straight from the PC to the MLC 9000 using a 485 connection.

I am also interested to hear any problems from people have had with the MLC 9000.

 

What happens if the Labview PC goes offline? Will the MLC9000 retain its setpoints, etc..? I know if the S7 is controlling setpoints through
profibus, your still fine without the PC. You also have some flexibliity of adding an operator interface, I/O, etc.. with having a profibus
network.

 

The MLC9000 maintains all its setup parameters internally and independent of whatever HMI or comms link you choose.