Simulation and experimental development of a temperature control system of a radiation calibration source based on a PID-regulyator

Improvement of methods of radiometric correction for multichannel spectral hardware and wide usage of LED-sources require the development of both mathematical and experimental methods of calibration of the obtained spectral data. To obtain true coefficients of spectral reflection it is necessary to use high-stable radiation sources, which makes it possible to improve measuring accuracy, to perform a transition from absolute to relative units of measure. Application of high-brightness LEDs for the purposes of radiometric calibration is limited by variations of their characteristics over time, degradation of structures and temperature drift of characteristics. To stabilize the spectral LED radiation maximum we need to resort to additional methods for the temperature control of radiation sources by controlling dissipation power on the crystal, taking into account high nonlinearity of the dissipation curve of the crystal depending on the passing current. The nonlinearity of the processes of the crystal heat release at the optimum operation point calls for the application of a high-precision mode of temperature control. A technique of “proportional integral-derivative” temperature control for light-emitting diodes of increased brightness with phosphor-coated crystals was developed and experimentally tested. The possibility of using temperature control of a highly stable source to stabilize spectral characteristics is shown. It allows using this technique to increase the accuracy of assessing the optical properties of the surface under investigation.