The invention relates to a method of producing alkoxycinnamic acid ester by condensing C5-C8 acetic acid esters with C1-C4 alkoxybenzaldehyde in the presence of an alkaline andor alkaline earth C1-C4 alcohalate and removing the C1-C4 alcohol that is produced by this reaction from the reaction mixture. According to the invention, a target value,. A drop weight is installed within the column. The method includes detecting a plurality of reference transmitted light intensities for the at least one reference chamber and estimating a value between the plurality of reference transmitted light intensities through nonlinear approximation. Additionally, the control module may be operable to synchronize the various control signals, obtain a representative sample of the current through the voltage converter, and operate in different modes.