Device for determining the frequency of alternating electrical quantities, particularly of a rotating-field machine

摘要

An angle ( alpha ) can be allocated to two alternating quantities (a1, a2) by means of the relation a1 DIVIDED a2=ctg alpha A quantity (w) corresponding to the change of this angle with time (frequency) is to be determined. For this purpose, the alternating quantity (a1) is connected to a first multiplier (M1) and the alternating quantity (a2) and the change of the alternating quantity (a1) with time is connected to a second multiplier (M2) and the quantity (w) is picked up at a following subtracting circuit (3). The frequency can be obtained directly if the alternating quantities are in each case connected to a squaring circuit (12, 13), the outputs of the squaring circuit are added together and the quantity (w) is divided by this sum. <IMAGE>