Ah. This still isn't clear. Does your Scada application publish changes? Does it provide some kind of API that provides hooks to detect changes? Is it a GUI app with a Windows form interface that provides a display of the values? There are a lot of unknowns here.
You say you are already fetching the values from the Scada software, which seems to indicate that you have some kind of API. So... the values are coming in, you need to check if they have changed, and then log the changes - seems like you already have everything you need. What specifically isn't working?
Woody Z http://www.learntoprogramnow.com