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power meter[′pau̇·ər ‚mēd·ər]
an instrument for measuring the power of the electromagnetic oscillations generated by oscillators, amplifiers, radio transmitters, and other devices operating in the high-frequency, superhigh-frequency, or optical regions. Power meters may measure absorbed or transmitted power. The first type of meter is used to measure the total power dissipated in a load; the second type measures the portion of the power that reaches the load through a wave-guide or coaxial transmission line (if the division coefficient is known). Power meters are classified according to method of measurement as calorimetric, bolometric, thermoelectric, ponderomotive, and so on.
The operation of a calorimetric power meter is based on conversion of the energy of electromagnetic oscillations to heat and measurement of the quantity of heat according to the flow of a heat-transfer agent (usually water) flowing through the load and according to the temperature difference of the heat carrier entering and leaving the load. Calorimetric power meters are used for power measurements in the intermediate range from 1 watt (W) to 0.1 megawatt (MW) and for frequencies from 0.01 to 100 gigahertz (GHz); their error is 5–10 percent (for standard meters, 1–3 percent).
Bolometric meters record the change in electrical resistance of a bolometer or thermistor connected to the arms of a bridge when electromagnetic oscillations are fed to them. Bolometric power meters have the advantage of high sensitivity.
In thermoelectric power meters the energy of electromagnetic oscillations is converted by a thermocouple into a voltage, which is amplified and fed to a dial or digital indicator calibrated directly in units of power. The limits of measurement are 0.01 microwatt (μ W) to 10 milliwatts (Mw) for bolometric power meters and 1 μW to 10 mW for thermoelectric power meters. These limits may be expanded by the use of attenuators. Such power meters operate at frequencies from a few megahertz to tens of gigahertz (in coaxial channels) and even hundreds of gigahertz; their error is 5–10 percent.
Torsional ponderomotive power meters are based on measurement of the torque generated by the interaction between an electromagnetic field and a current induced in a stationary component (a plate or frame suspended from an elastic filament). Ponderomotive power meters have an error of 0.5–1.5 percent; the measurement limits are from tens of milliwatts to tens of kilowatts. They are used as standards for calibrating power meters of other types.
REFERENCESValitov, R. A., and V. N. Sretenskii. Radiotekhnicheskie izmereniia. Moscow, 1970.
Shkurin, G. P. Spravochnik po elektro- i elektronno-izmeritel’nym priboram. Moscow, 1972.
E. G. BILYK