GB801495A - Means for indicating differences in rotational speeds - Google Patents

Abstract

801,495. Electric correspondence control. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. March 20, 1956 [March 23, 1955], No. 8618/56. Class 40 (1). Means for indicating differences in rotational speeds comprises two alternating voltage tachometer generators 1, 2 which at zero speed difference provide alternating voltages of equal frequencies the alternating voltages being added and supplied to an indicating means consisting of a rectifier 7 followed by a smoothing filter 9, 10 which is so dimensioned that it cannot smooth frequencies substantially corresponding to the speed difference to be indicated and a relay means 11, which is arranged to react when the instantaneous value of the voltage from the smoothing filter falls below a predetermined value. As shown, the relay means comprises a thermionic valve 11 and this may have a relay connected in its anode circuit, the relay being arranged to control, for example, a mechanical coupling between a starting motor and a rotating load having a large inertia. In such a case one of the tachometer generators is driven by the starting motor and the other by the load. The outputs of the tachometer generators are applied to the rectifier 7 through equal resistances 3, 4. When the speed differences are large the output of the smoothing filter is a negative D.C. voltage which is sufficient to bias the valve 11 to cut-off, but as the frequency difference falls the filter output changes to varying D.C. and when the minimum instantaneous value of the D.C. voltage falls low enough the valve 11 is enabled to conduct and so operates the relay. A voltage source 14 can be connected between the capacitor 10 and the grid of the valve 11 to change its cut-off voltage. In a modification the generator outputs may be applied to the rectifier 7 through a transformer 7.