A system is provided to adjust a separation distance between a read/write sensing head and a data storage medium surface in a hard disk. The thermal expansion of the sensing head based on heat generated by power dissipated through the sensing head is precisely controlled. When electrical resistance is not accurately known, a calibration is performed in which a specific input value is matched to a predetermined reference electrical power. The matching is done through a reference voltage source, that remains at a fixed value, and a calibration factor is successively adjusted through a feedback loop until an optimum value of the calibration factor is obtained. At the conclusion of the calibration process, the feedback loop is disabled and the optimally attained value of the calibration constant is frozen. The electronic circuit to implement the proposed system is based on cost effective CMOS technology.