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in electrical and radio engineering, a precision device for tuning and calibration of measuring instruments (determination of errors or correction of scale values). Its operation is based on comparison to a standard of the value being measured.
Calibration generators operating on several strictly defined frequencies from 100 hertz (Hz) to 100 megahertz (MHz) are usually used for frequency calibration of frequency meters, standard-signal generators, radio reception and transmission equipment, and other instruments with a continuously variable tuning range. Electrical oscillations are supplied by a piezoelec-trically stabilized generator with a relative frequency error of up to ±1 × 10”-5. In addition to the fundamental frequencies, harmonics of the fundamental frequencies in the range of 20-40 gigahertz (GHz) are also used. In a continuous frequency range heterodyne frequency meters are also used for this purpose. A calibrating generator usually consists of a reference crystal oscillator, a frequency converter, a mixer-detector, and an audiofrequency amplifier, which make possible calibration without any additional apparatus. The principle of operation of a calibrator is based on a comparison of the frequency being measured with the fundamental frequency (or one of its harmonics) of a crystal oscillator and separation of the difference frequency by the zero-beat method in a mixer-detector.
Frequency standards are calibrated by means of receiver comparators according to the signals of radio stations transmitting on superlong wavelengths. Under certain conditions of propagation of long waves (a = 10, 000 m), phase stability over a 24-hour period makes possible highly precise comparison of the frequency of the signals received to standard frequencies. In 1970 there were seven radio stations that regularly transmitted signals of great frequency precision. Their signals could be received throughout the world. Calibrators also exist for checking the voltage indicated by electron-tube voltmeters; they are called calibration voltage sources (for direct and alternating current).
Calibrators are also used for precision work in metrology, for measuring sets of standards, and for calibrating instrument scales. Calibration should not be confused with graduation, which is a metrological operation that consists in the division of an instrument scale into units established for it.
REFERENCESMalikov, M. F. Osnovy metrologii, part 1. Moscow, 1949.
Izmereniia v elektrotekhnike: Spravochnik, vol. 1. Compiled by B.A. Dobrokhotov. Moscow-Leningrad, 1965.
Shkurin, G. P. Spravochnik po elektroizmeritel’nym i radioizmerit’nym priboram, 3rd ed., vols. 1-2. Moscow, 1960.
V. V. BOGOMAZOV