You might be right about PTCs though I now can't remember exact reason for choosing PT100. It probably wasn't just linearity. I think I had other problems like

You might be right about PTCs though I now can't remember exact reason for choosing PT100. It probably wasn't just linearity. I think I had other problems like controlling amount of power dissipated on the sensor (large changes in resistance mean large changes in amount of power dissipated) and possibly other.