Thank you every body for your replies. I didn't know the audio inputs were AC coupled.
Actually, they very often are not AC coupled. You ought to be able to find out if yours are using Audacity and a signal source.
Matlab has a function that can use the sound card for IO, so it is practical.
I am using an arduino to measure spindle temp and offset z automagically..
I followed these examples..
works very well so far
Arduino is a very simple way to achieve DC analog readings.
arduino uno R3: www.ebay.com.au/itm/EKitsZone-UNO-R3-ATM...&hash=item3a8184cae3