| 摘要 |
An indicator, and method of indicating, the expiration of substantially the predetermined useful life of a water filter, use color change in a simple but very effective manner. The water migrates into a color change mechanism which may include a porous medium, and causes first and second reagents to react producing a color change. The reaction system between the reagents may be selected from the group consisting essentially of chelation of a metal ion by a chelating agent, reaction of an acid/base with a pH indicator, reaction of an electron donor/acceptor with a redox indicator, and an enzymatic reaction between an enzyme and a substrate. The color change mechanism displays a gradual advance of the color change over time, and may incorporate a scale to display the elapsed time. A mask containing scale indicia may be used to relate the progress of the diffusion to substantially the predetermined useful life of the filter. |
