The SP-42AF is a tin dioxide semiconductor gas sensor which has a high sensitivity to HFCs (e.g. Freon: R407C) with improved cross sensitivity to other gases. This sensor maintains strong resistance to chemical poisoning by a filter installed inside the sensor housing.
Gas sensitive semiconductor material is formed on the alumina substrate on which the gold electrodes are printed. A thick film heater of ruthenium oxide is printed on the reverse of the substrate and placed in the plastic housing which uses double stainless-steel mesh (100 mesh) in the path of gas flow. This sensor has silicon poison proof silica filter.