We have worked for two seperate customers where we installed ethernet modems on lease lines and connect to the remote PLC's using a Modbus driver and selecting Modbus ethernet mode and have had good luck with that. The poll rates we have set are between 1 to 3 secs. The server on one site currently is looking at 9 sites.
We had some situations where the lease lines were being abandoned so we have now switch most of the sites to wireless ethernet radios and are having excellent results.
We have not tried cable but using the radios and ethernet have worked well. Previous to the conversion to ethernet modems we were using serial modems. With the serial modems we needed to transfer all the data to a master PLC and then have Lookout Poll the master PLC. The poll times there were longer due to the nature of the polling updates.
Mike
