The electrochemical analysers available in the market assert trustworthy values applicable in a specific uncertainty range, which varies depending on the unit`s model.Nevertheless, rarely is given any information on the time necessary to reach these values, which depend on the answer of the instrument. This Master`s dissertation aims to develop an experimental theoretical methodology to evaluate the performance of the transducer in transient conditions, and obtain some typical values for commercial analysers, and its answer in the pH measurements in simulated chemical reactions in various reaction velocities. Through the qualified model, the errors due to the permanent and transient answers were evaluated, establishing the conditions pH electronic units can be used, in a pre-set controlled error, from the comparison between real pH values and displayed pH values in the analysers, considering the temperature and the reaction time.