Swerea KIMAB AB has developed a method to study surface reduction on powders and solid materials with the help of a Photo Acoustic Spectroscopy instrument (abbreviated to PAS). The strength of the PAS method is the continuous gas registrations with a very high precision (i.e. down to less than 1ppm). Furthermore, by combining the PAS results together with thermodynamic calculations a deep understanding is gained in the area of surface reduction during heat treatment. PAS is a highly sensitive technique by which ppm levels of different gases within a carrier gas can be measured. This unit is calibrated to measure CO, CO2, CH4, H2O and dew point. The PAS furnace at Swerea KIMAB AB has been modified at in order to improve three main parts of the experimental setup to achieve a purer furnace atmosphere, a possibility to fast cool samples, and a more accurate temperature control.