Patent ID: 7480577

Claim:
A method of determining an overall rate of flow of a fluid by combining local flow signals from two or more local flow sensors, each of the local flow sensors trusted to provide an accurate respective local flow signal during a learning period, each of the local sensors subject to failure during an operational period subsequent to the learning period, the method comprising the steps of: calculating, at each of a plurality of times during the learning period, a respective current composite flow value representative of the current overall rate of flow of the fluid by applying a flow-calculating algorithm to a set of all of the local flow signals and storing in a memory, for each of the composite flow values calculated during the learning period, a calibration record comprising at least the respective composite flow value and each of the local flow signals from which it was calculated to thereby build a calibration table; determining, at any instant within the learning period, if the then current composite flow value is equal to an earlier composite flow value and, if so, combining each of the then current local flow signals with the corresponding local flow signal associated with the earlier composite flow value; and at each of a plurality of times during the operational period: applying a test algorithm to each of the current local flow signals to determine if one of the local sensors has failed and if it has, modifying the set of all local flow signals by replacing the current local flow signal of the failed one of the sensors with a corresponding value from the calibration table and calculating the overall rate of flow by applying the flow-calculating algorithm to the modified set of local flow signals; and otherwise calculating the overall rate of flow by applying the flow-calculating algorithm to the set of current local flow signals.