quiqueapolo:
Thanks:
I think is necesary negative voltage because I need to read thermistor. I try your code. However the values of mV are like this in the Monitor Serie:
12
7
42923467
The values change too much!
the 1st and 3rd value you posted should be the thermistor value... since its not "excited" with the correct voltage level, the values as basically garbage.
The 2nd value you get is your thermopile. Check every 2nd value you get and covert the mV to DegC. you should see sensible value there IMO.
you need to build some hardware then to cater for the -ve voltage. how do you plan on powering your arduino?
If it's from battery, I have already shared with you in my previous post a link for a circuit that would help you do that. If its from mains then just get one that's either dual supply or actually have a -ve voltage supply on it (either way you then would need to bring it up to -2.5V... another simple circuit can do that! 
)
Next you need to devise a method to switch between the 3.3V and -2.5V to be get the outputs of the thermopile and thermistor receptively.
Lastly you need to pass the output of the thermistor (brown wire) through an inverting amplifier to get the absolute value that you then feed into the arduino's analog input.