This paper falls within the context of diagnosis of rotating machines in speed variableregime. Based on simulation signals, this work has the purpose to find relevant indicatorsfor the diagnosis of gear transmissions in a variable regime. Two indicators are proposed;the first indicator is the RMS value applied to the vibration signal divided by itscorresponding instantaneous frequency. The second is the normalised gear frequency byaveraging speed. The gear frequency and averaging speed are estimated from thespectrogram. To test the proposed indicators simulate signals have been used. Thesesignals are the results of a dynamic modelling of the gears transmission and arecalculated by using the Newmark integration diagram. This dynamic modelling takes intoaccount the eccentricity defect.
