Patent ID: 8616045

Claim:
A method for deriving the concentration of a gas dissolved in an electrical insulating oil ( 2 ) of an electrical apparatus, comprising the following steps: preparing a membrane ( 5 ) permeable to the gas, interposed between a container ( 7 ) of the oil ( 2 ) and a measuring chamber ( 4 ) that receives a part of the gas through the membrane ( 5 ); measuring the value of gas concentration in the measuring chamber ( 4 ); deriving an estimated value of the concentration of the gas in the oil ( 2 ) as a function of the measured value, characterized in that: measuring comprises taking at successive measuring instants a plurality of measurements of the values of gas concentration in the measuring chamber ( 4 ); deriving comprises calculating the estimated value of gas concentration in the oil ( 2 ), at an instant selected from said measuring instants, according to a non-linear function of the values measured at the selected measuring instant and at one or more of the measuring instants preceding the one selected.