Frequency Measurements with the Cathode Ray Oscillograph

Abstract

The cathode ray oscillograph frequency measurement circuit described differs from previous circuits in the use of by-pass condensers and plate leaks which permit connection of the oscillograph to a-c. circuits having large d-c. components and which permit the use of biasing controls for shifting the position of patterns on the screen. Reference oscillators are used in conjunction with the frequency standards. They are of a type chosen. for their high stability. The well-known properties of Lissajous' figures are reviewed briefly and then developed more fully for the cases in which only one term of their ratios may be determined from the oscillograph pattern. Following a general discussion of the accuracy of syntonization, there is discussed a detailed method of calibrating oscillators. The patterns used may be interpreted from one term of their ratio. Interpolation formulas are derived for use in making interpolations on the reference oscillators. The methods of interpolation discussed may be used for intervals up to 0.5 per cent frequency with high degrees of accuracy. The interpolation formulas are extended further in the development of approximation methods by which any unknown frequency may be quickly determined within a few per cent. Several special circuits are described for use infrequency measurements work with the cathode ray oscillograph. The methods and apparatus described are suitable not only for the technical measurements of a development and research nature but are equally adaptable for routine commercial work.