Control of Temperature Variation in the Frequency of Tuning Forks (with demonstrations)

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The increasing use of tuning forks not only as frequency standards but as controlling devices for equipment requiring perfect synchronization calls either for very accurate temperature control with the ordinary steel fork, or for the development of forks in which the variation of frequency with temperature is negligibly small. Two methods have been employed to achieve this end—either the development of metal alloys having very small frequency-temperature coefficients, or the fabrication of compensated forks from two materials having coefficients of opposite sign. While alloy steels, such as Invar and Elinvar, can be produced having coefficients of the order of one-twentieth that of ordinary steel, yet very considerable variations in coefficients are found in individual samples of these alloys even when cut from the same piece of stock. The combination of two alloys having positive and negative temperature coefficients has proven a more practical means of producing forks of uniform qualities and with frequencies independent of temperature. Demonstrations of the thermal properties of forks of this type will be made.