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phase shifter[′fāz ‚shif·tər]
a device used in automation, conversion technology, and measuring technology to change the phase of electromagnetic oscillations. The design of a phase shifter depends on the range of operating frequencies, the limits of the phase change, and the accuracy of the equipment. Four-pole networks consisting of resistors, induction coils, and capacitances are usually used as phase shifters for low frequencies and in the radio-frequency range (up to several megahertz).
The simplest type of phase shifter consists of a phase-shift circuit composed of a resistor and a capacitor or of a resistor and an induction coil. Such phase shifters are usually used to produce a fixed phase shift within a range from 0° to 90°. More advanced types consist of a bridge circuit with three resistors and one capacitor; such designs produce an adjustable phase shift in the range from 0° to 180° with small changes in the magnitude of the output signal. Transistor and electron-tube phase shifters with bridge circuits are also used; they feature a phase inverter with a divided load as one of the network components. The phase shift produced is 180°. In the designs mentioned, the phase shift obtained depends on the frequency. This drawback is eliminated in follow-up phase shifters, in which any deviation of the phase shift from a specified value is automatically corrected by changing the parameters in such a way that the deviation is reduced.
Rotary transformers, selsyns, and three-phase asynchronous electric motors with blocked rotors are used for phase adjustment in AC circuits powered from mains rated at frequencies standardized for industry. Phase shifters for decimeter and shorter wavelengths are assembled from sections of coaxial lines and waveguides. The error of phase adjustment is from 0.5° to 1° for electromechanical phase shifters and from 0.05° to 0.1° for electronic phase shifters.
REFERENCESValitov, R. A., and V. N. Sretenskii. Radiotekhnicheskie izmereniia. Moscow, 1970.
Avramenko, V. L., Iu. P. Galiamichev, and A. A. Lanne. Elektricheskie linii zaderzhki i fazovrashchateli (handbook). Moscow, 1973.
Kushnir, F. V. Radiotekhnicheskie izmereniia, 3rd ed. Moscow, 1975.