We examine how the thermal‐pulse technique for determining spatial charge distribution in charged polymer foils is affected by inaccuracies of the measuring process. A theoretical model is developed for thermal equalization processes which is in agreement with the measured temperature transients. Using this model, we show by computer simulation that even for a measurement inaccuracy of less than 1% the obtainable information consists of only the first moment of the charge distribution and the first few Fourier coefficients.