temperature monitoring alarm system

Hi, I'm new around here and haven't ever used an arduino. Im in the process of building a temperature monitoring alarm system with up to 50 temperature sensors. i was thinking of using DS18B20 sensors and a Arduino. From the arduino i want to send the data via mod bus to a PLC which is part of my local network. can this be done with an Ethernet connection? And what kind of arduino would work best for this application? Thanks for any help.

Search in this page for DS18B20 : Arduino Playground - InterfacingWithHardware
Perhaps you find some new ideas.

I don't know the ModBus. Does it use RS485 ?
http://playground.arduino.cc/Code/ModbusMaster

There are expansion shields with RS485.
If you could make them work with ModBus, you have a reliable connection.

If you have ethernet cables, you could use an Ethernet Shield, or an Arduino Ethernet. But using ethernet is slow, and it doesn't handle slow or bad connections very well.

In the playground is the ModbusMaster Library.

http://playground.arduino.cc/Code/ModbusMaster

Google search

These are RS-485 options. You can get RS-485 to Ethernet converters. Where I work we use a RS-485/RS-232 converter then connect to the network with a Lantronix converter. I see they have a new product:
xDirect Serial-to-Ethernet Device Server | Lantronix for $110