The current and the phase angle of the internal beam with respect to the accelerating voltage of the Eindhoven University of Technology AVF cyclotron are measured using a number of electrostatic induction pick‐up probes. Data handling is by means of sampling, correlating, and a CAMAC system. On the hf signal is superimposed a very strong first (fundamental) harmonic signal induced by the accelerating voltage. Therefore, the second harmonic component of the probe signal is used. Furthermore, all odd harmonic components of the signal are suppressed by using a special sampling technique. For the first harmonic component the suppression is about 60 dB.