[en] Complete text of publication follows. The electron energy is one of the main parameters that (together with the density and atomic composition of the product, size and shape of the product and its orientation to the electron beam) influence the dose distribution inside a product treated with a beam of energetic electrons. An easy to use and robust device has been developed that can reliably detect day-to-day small variations in the beam energy. It consists of two aluminium plates, which are electrically insulated from each other; they are identical except for their thickness. The thickness of each plate is carefully selected depending on the electron beam energy. The charge (or current) collected by each plate, while under the beam, is measured by an electrometer. The ratio of the charge (or current) signal from the front plate to the sum of the signals from the front and rear plates is very sensitive to the beam energy. We have tested this device with two different accelerators with beam energy of 3 and 12 MeV. The high sensitivity and robustness make this device quite suitable for process control applications at an e-beam radiation processing facility