Talking to Eurotherm 2416 temperature controller over modbus rs232
You could also take a look at this github project:
https://github.com/ukos-git/arduino-eurotherm2416

It is specifically designed for the purpose you ask for. 
It basically includes Module named Temperature and a possibility to set or read it:

Temperature.set(100)
t = Temperature.getTemperature()


Look at https://github.com/ukos-git/arduino-eurotherm2416/blob/master/app/app.ino.