The temperature of glass during the tempering process plays an important role. To ensure the best glass quality, the temperature values of the glass must match the specific glass recipe. In addition, the temperature profile of the glass gives some feedback about the furnace condition. The measurement of the glass temperature during the tempering process is used for quality assurance and monitoring of the furnace. Accordingly, it is important to measure correctly.

The paper explains typical challenges during the glass temperature measurement and how it can be solved. There are optical issues as well as mechanical issues to be considered. Since there is no coating on the downside of the glass the best and most precise way to measure the glass is the measurement from underneath. The limited space between ground and glass needs an optical system which can “see” the whole width of the glass. At the same time the case of glass breakage needs to be observed. Which means falling glass must not harm the measurement device.

The most promising approach for such measurement is the usage of two IR-cameras which measuring upwards to the downside of the glass. One complete image is created from both cameras. Each camera is protected with a shutter system which close in case of glass breakage.