Pyrometric temperature measurements with a miniature cavity used as a blackbody in the calorimetric method for determining absorbed laser energy

• The paper deals with temperature measurements by calorimetric method.
• A set-up for pyrometric measurements of temperature was built.
• The temperature of metal samples subjected to laser welding was measured.
• Analysis included the effect of black body on the measurement quality.
• The efficiency of the use of black body in the calorimetric method was shown.

As a result of improvements introduced in the design parameters of detectors, the miniaturization of measuring gauge and software upgrades, today’s single band pyrometers are robust devices with innovative solutions developed to enhance their performance. Despite technological advances, entering the correct value of emissivity coefficient of an object in the pyrometric measuring system is still an unsolved problem. One of the possible solutions may be using a blackbody to a greater extent. This study attempts to use a miniature cavity as a blackbody in pyrometric temperature measurements of a metal part, conducted according to the so-called calorimetric (thermometric) method of determining the laser energy transferred to the part. The method helps measure the temperature of a laser-processed material that acts as a calorimeter. Temperatures are normally measured using thermocouples bonded to the laser-treated element, but this technique is not free from limitations. Some of them can be eliminated through pyrometric measurements. The experimental investigations involved simultaneous temperature measurements with the use of a thermocouple fixed to the processed element and a pyrometer for measuring the temperature of the miniature blackbody cavity produced in the material. Comparative study results support the use of a blackbody for calorimetric non-contact temperature measurements of laser energy absorbed in the welded part in laser beam welding.