[en] This contribution summarizes the current implementation of the time-of-flight (TOF) energy analysis for plasma potential measurements by the heavy ion beam diagnostic (HIBD) on the tokamak ISTTOK. The technique is described in detail. The results of the measurements of the ISTTOK plasma potential radial profile are presented. It is proved that the TOF energy analysis is suitable for simultaneous multichannel detection using a multiple cell array detector. With the aim of improving the signal-to-noise ratio of the diagnostic, the channeltrons have recently been installed on the 'start' and 'stop' detectors and preliminary results are discussed