Digital Holographic Interferometry(DHI)Used in the Measurement of Temperature Field
|School||Chongqing University of Technology|
|Course||Mechanical Design and Theory|
|Keywords||digital holography digital holographic interferometry temperaturefield subtraction digital holography Butterworth low-pass filter|
Temperature is an important physical parameter, which is closely linked with people’s lives and production. Temperature field measurements play an important role in the modern scientific research and national economic development. There are many methods about the measurement of the temperature field, and this paper presents digital holographic interferometry (DHI) for the measurement of the temperature field. DHI inherited the advantages of traditional optical holography measuring temperature field, which record changes in the refractive index result from the changes in temperature as the form of interference fringes, and DHI doesn’t need to contact with the target temperature field, so it would n’t introduce new errors. Besides, Digital holographic interferometry has its own advantages, which use photoelectric Coupled Device (CCD) as a recording medium replace the traditional holographic plate to record the temperature field. Information can be stored in a computer for processing by CCD, So it avoid a lot of tedious procedures, saving some time and increasing efficiency greatly.The paper analysis the two basic types of digital holographic recording optical path including in line holography and off-axis holography, which have each advantages and the scope of application. The paper selects the off-axis digital holographic optical path as the ultimate optical path. Convolution approach and Fresnel approximation as two basic digital holographic reconstruction algorithms are introduced. This paper studies the axisymmetric temperature field. In the experiment, We use the optical path record two states of the temperature field around a Soldering iron core (before and after heating).The method of subtraction digital hologram is proposed to obtain a clear interference fringe pattern, and these stripes recorded temperature field. Butterworth low-pass filter is used to process interferogram to obtain better binary image, the experiment verified it. Using the classic Hilditch algorithm refinement operation on the binary image, centerline of the stripes can be extracted. Although "bifurcation" phenomenon still exist, the overall effect is good. Derived a relationship between the interference fringe level and fringe displacement, combined with the data obtained in image, a function of the temperature distribution around the electric iron core is obtained. Compare it with the heat conduction equation in theory, from the figure, it can be see that two curves nearly have the same trend, but there are some gaps. The possible causes of error are analyzed. Taking into account these possible causes, it can conclude that digital holographic interferometry technique can be used for the measurement of temperature field, it could record the change of the temperature field, but it need to do some restrictions on environmental conditions to acquire accurate value. So researchers need to make greater efforts to break through these barriers.