Application of lock-in methods for measuring radiation temperature
For years, radiation temperature measurement was the classical application of IR thermography. Nowadays, we observe new, the unconventional use of this technique in numerous domains for indirect process monitoring and measurement. One of the example of such application is the RMS electrical current measurement in outdoor power cables with eliminated effect of convective cooling and solar radiation. Furthermore, there is a need of measuring distributions of temperature changes at the very low level, below the noise limits of today’s IR systems.
Application of heterodyne and homodyne systems is one of the possible measurements of radiation temperature at low level. This approach was successfully applied for AC electrical power networks. Radiation aspects of temperature changes of a conductor transporting electricity, along with load changes, is a significant problem in the power industry. Forced and natural convection problems are studied and analyzed all over the world. One of the main research aspects carried out at the Institute of Electronics is the quality of electricity - a parameter of the value of alternating current and the accompanying temperature changes.
As a result of the carried-out work, it was possible to develop a novel and innovative method of RMS current measurement, for which an IR camera is required. The 2- ω method is based on Fourier transformation and analysis of the generated second harmonic signal. So far, the research has concluded that the measurement method is resistant to the influence of external light and weather conditions, such as excessive wind speed and direction. Performing an appropriate calibration of temperature and current changes in the tested element allows achieving the accuracy of changes at the level of µK. The 2- ω method is now under the patent approval process.
The accuracy of measurements using the new 2- ω method as well as the limit of its application using available thermal cameras is going to be verified. Further works in this field will lead to the measurement of temperature in the very thin structure of the semiconductor power devices. The proposed method will be implemented in the synchronous temperature measurement for testing electronic and power systems, especially based on latest gallium nitride technology.
- B. Torzyk, B. Więcek, A method of RMS current measurement in low and medium voltage AC electrical cables, Polish patent submission, 28.01.2019, no. 428676.
- B. Torzyk, B. Więcek, Thermal modeling and RMS current measurement in electrical power lines using IR thermography, Measurement Automation Monitoring, no. 3/2018, pp. 53-56.