GB371014A - Improvements in or relating to electric frequency meters - Google Patents

Abstract

371,014. Frequency measurements- SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Jan. 8, 1931, No. 705. Convention date, Jan. 17, 1930. [Class 37.] In a frequency measuring device utilizing the change of phase in a tuned circuit when it is energized by current at a frequency other than its natural frequency, the tuned circuit comprising a condenser 3 and inductance 4 is connected to the supply frequency terminals 1, 2 in series with a resistance 5. A.D.C. measuring instrument 6 such as a moving coil instrument, is connected across the resistance 5 in series with the contacts 7 of a mechanical rectifier, such as a diaphragm rectifier, the coil 8 of which is energized from the terminals 1, 2 of the supply frequency in series with a condenser 9 or variable choking coil or other phase displacer, by a current 90‹ out of phase with the applied voltage. When the applied frequency is the same as the natural frequency of the tuned circuit, the rectifier contacts are arranged to permit the flow of equal positive and negative parts of the cycle through the instrument 6 which has a centre zero. When the applied frequency differs from the frequency of the tuned circuit the phase of the current in the latter varies with respect to the applied voltage and also the current energizing the rectifier. Accordingly, the rectifier contacts are closed for a different 180‹ part of the cycle of current in the tuned circuit and the resultant current, positive or negative, after rectification, deflects the pointer of the instrument 6 one way or the other. To eliminate the effect of potential fluctuations, the measuring instrument may be a cross coil instrument, the directing coil of which is supplied through a rectifier, e.g. a copper oxide rectifier, from the supply to be measured. Alternatively, a constant potential circuit may be used to supply the tuned circuit. The measuring instrument may be an oscillograph or an ampere-hour meter. In the latter case the measurement is converted into electrical impulses which are transmitted to distant points and there actuate an indicating instrument. A constant turning movement may be given to the meter with the measured turning moment superposed thereon, or the latter alone may act on the meter in which case the direction of rotation of the meter must also be transmitted. Alternatively, in the latter method, the energizing phase of the rectifier 7, 8 may be adjusted so that the direct current fluctuates between maximum and minimum values but does not change direction, in which case the direction of rotation of the meter is not transmitted.