A method for measuring thermal resistance between a thermal component of an instrument and a consumable includes contacting a known consumable with a thermal component to be tested; driving the thermal component using a periodic sine wave input based on a predetermined interrogation frequency; measuring temperature outputs from a thermal sensor responsive to the periodic sine wave input; multiplying the temperature outputs by a reference signal in phase with the periodic sine wave input and calculating the resultant DC signal component to determine an in-phase component X; multiplying the plurality of temperature outputs by a 90° phase-shifted reference signal and calculating the resultant DC signal component to determine a quadrature, out-of-phase component Y; calculating a phase offset responsive to the periodic sine wave input based on tan−1 (Y/X) or a tan 2(X,Y); and determining a resistance value for the thermal interface using a calibrated resistance-phase offset equation and the calculated phase offset.