The operating temperature increase of electric energy production equipments is a sign of poor performance or the need of maintenance before critical limits be attained. As a diagnostic tool, the interpretation of the infrared signal, as received by a camera that registers the image of a target, is often used and referred as a thermographic camera. In this work, a methodology was developed to interpret the infrared signal from a camera, aiming a maintenance planning. Initially, a device was designed to calibrate the thermographic camera at PUC-Rio. It consists of a cylindrical brass block, placed inside a controlled temperature bath, having its upper surface painted black and placed about 3 mm above the liquid surface of the bath. Holes were drilled radially, slightly bellow the block upper surface, so that its temperature could be measured by inserted thermocouples. Next, the instrument was calibrated with a black body at INMETRO. The surface emissivity was calculated as a result of the comparison between the calibration results in PUC-Rio and INMETRO. After calibration, the impact of the uncertainty of several parameters in temperature measurement was calculated, following the procedures that are presently adopted by the electric energy utility company LIGHT ENERGIA S.A., so that to optimize the maintenance procedure of equipments.