Abstract: In a control device which includes an integrating positioning drive comprising a motor and transmission with backlash and lag, the backlash being the hysteresis of the transmission of mechanical quantities which occurs when the direction of rotation changes and which is caused, for example, by gear tolerances in the transmission due to manufacturng constrains, in addition to a first feedback path which supplies a signal proportional to the position of a control member, there is also provided a second feedback path developing a signal dependent on the positioning rate and the magnitude of the lag in the motor and, the mechanical members of the positioning drive are designed in such a manner that the transmission lag which occurs is greater than the sum of the position changes of the control member during starting of the positioning member over the period from stand-still to reaching its nominal speed and the position change occuring during the lag after the positioning motor is deenergized, providing a control

Abstract: A method of operating turbo compressors. To prevent pumping surges, blow-off valves are opened upon reaching a blow-off line extending parallel, with respect to time, to the pumping limit. The difference between the compressor discharge pressure and flow rate and the blow-off line is non-linearly amplified in a manner related to the actual pressure and flow rate so that the amplification gain is increased if the operating point of the compressor shifts into the non-permissible range beyond the blow-off line. Special provisions are made for starting the compressor.