Abstract: When, according to the invention, constructing a drive system for rotating a cleaning head in a tank and allowing the system to comprise a hysteresis coupling having two magnetic parts, one being present inside the liquid space (4) and the other outside the liquid space, respectively, a completely liquid-tight separation between the housing (2) and a gear (14) may be ensured. The magnetic part (8, 18) of the hysteresis coupling may be formed by electromagnets, and with a displaceable (13) position of one part relative to the other part (11, 19), the coupling may be adjusted with respect to the transferred torque and/or speed.

Abstract: When, according to the invention, a cleaning head is provided with a hysteresis coupling (9, 11) between the turbine (3) and the gear in the gear housing (13), the gear will remain separated from the turbine and not be subjected to liquid impact. The hysteresis coupling (9, 11) may be adjusted using electromagnets (9) as an inductor, which allows control/regulation of the rotating movements of the cleaning head to achieve the best possible cleaning pattern.

Abstract: When, according to the invention, constructing a drive system for rotating a cleaning head in a tank and allowing the system to comprise a hysteresis coupling having two magnetic parts, one being present inside the liquid space (4) and the other outside the liquid space, respectively, a completely liquid-tight separation between the housing (2) and a gear (14) may be ensured. The magnetic part (8, 18) of the hysteresis coupling may be formed by electromagnets, and with a displaceable (13) position of one part relative to the other part (11,19), the coupling may be adjusted with respect to the transferred torque and/or speed.

Abstract: A detector circuit is to be used for measuring current by means of substantially identically wound ring core transformers, in which magnetomotive forces are induced by a main current. The magnetomotive forces are counteracted by magnetomotive forces induced by a compensating current. Two of the ring core transformers (2, 3) are magnetized in antiphase by means of a modulation signal. The detector circuit includes optionally a synchronous rectifier for providing an adjusting signal for the compensating current. According to the invention means are provided for compensating for possible differences between the two ring core transformers for the modulation signal. These means include a cornmon winding surrounding the two ring cores (2, 3), said common winding detecting a possible error signal used in a negative feedback loop which automatically seeks to establish an equilibrium.