Abstract: Compensation for errors in an amplitude conversion system caused by inaccuracies in and nonlinearities of system circuit components is realized by employing a self-compensation process in an amplitude measurement system (FIG. 1). In one embodiment first and second reference signals (from 111) are controllably supplied (under control of 105 via A1, A2SW1, SW2, 108, 112, 113 and 103) to a RMS-LOG converter circuit (104) to obtain a measure of the amplitudes of the reference signals (TA, TB) and convert the amplitudes into pulse signals. The pulse signals are supplied to a control circuit (105) for conversion into digital form and storage as reference numbers for future use. A test signal supplied from a remote location over a facility under evaluation is supplied (via T, R, 101, 102, 103) to the RMS-LOG converter (104) where the test signal amplitude (TMEAS) is measured and converted into a pulse signal.