In this paper the authors analyze various structures of proportional–integral–derivative (PID) regulators in the control system of the electro-hydraulic strength machine for determination of material characteristics under the controlled stress, strain and energy parameters (strain energy density). The aim of this work is to determine the appropriate structure of the PID controller, so as the control system can accurately follow up the reference signal. Changes of the controller settings, depending on amplitude and frequency of the reference signal, have been presented.