1. A method for identifying an unknown gas using a diffusion limited sensor providing an electrical signal output when exposed to the gas, comprising the steps of: disposing the sensor in a chamber of fixed volume and having a gas input and gas output through which the gas flows; connecting the chamber to a source of a known test gas of known concentration and known diffusion coefficient D k, opening the input to the chamber, and causing the sensor to be exposed to the known test gas until a steady state electrical signal output from the sensor is obtained; determining the time T k necessary for the sensor to attain a predetermined percentage of the steady state output; closing the input to the chamber and disconnecting the chamber from the source of the known test gas; connecting the chamber to a source of said unknown gas; opening the input to the chamber and determining the time T u necessary for the sensor to attain said predetermined percentage of a steady state output for the unknown gas; calculating a diffusion coefficient D u for the unknown gas by the formula D u &equals;D k ×(T k /T u ); and identifying the unknown gas by its calculated diffusion coefficient.