Heater is a surface heat source: in fact the heater is realized on a basis of printed circuit, with a regular distribution of the electrical resistance that permit to generate a uniform thermal flow. The surface between the heater and the heated object is copper that permit to reduce the dissipated power in connections. Moreover, to improve the uniformity of the heat flow, a metallic plan can be added so as to homogenize the temperature of the face in contact with the object to heat.
The electrical resistance of the heated zone is independent to the temperature: a measure of the supply current provides to know the total power dissipated by the element heated, independently of the temperature.