Patent ID: 8231839

Claim:
A colorimetric gas detector comprising a substrate, the substrate bearing a dry, self-contained color change material that can react with a target gas in an atmosphere being monitored wherein the reaction causes the material to alter a parameter indicative of one of absorption or radiation by the material, wherein color-change material is located on at least two discrete areas, and wherein a concentration of the color-change material in one discrete area is different from a concentration of the color-change material in a second discrete area, the first and the second areas being adjacent to each other on the substrate, wherein the color-change material is deposited on the substrate by printing and wherein the discrete areas are arranged in a repeating pattern on the substrate that allows periodic advancement of the substrate to bring a fresh length of the substrate with a fresh at least two discrete areas into a position so that sequential areas of the substrate are exposed to the target gas to make further measurements.