The SP-42A is a tin dioxide semiconductor gas sensor which has a high sensitivity to HFCs (e.g. Freon: R-134a) with improved cross sensitivity to other gases.
This model is suitable for R-134a, R-410a, R- 407c and other new freon family which contain R-134a
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.