1. A method for correcting an output from an electrochemical cell sensor, having an output responsive to a concentration of sensed species in a stream, a pressure and a temperature in an interactive non-linear relationship, comprising the steps of: (a) providing an pressure sensor for producing an output responsive to a pressure in proximity to the electrochemical sensor; (b) providing a temperature sensor for producing an output responsive to a temperature of said electrochemical sensor; and (c) processing the outputs of the electrochemical sensor, pressure sensor and temperature sensor in a neural network having an output function which compensates said electrochemical sensor for changes in pressure and temperature to indicate a concentration of the sensed species.