page_title: Wattmeter
hierarchical_section_title: Wattmeter
caption_attribution_description: Wattmeter showing forward or reflected power, on the MEF-33 remote control unit of an SCR-522 (BC-624/625, Swiss army designation SE-013) VHF aircraft transceiver
context_page_description: The wattmeter is an instrument for measuring the electric power in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.
  A wattmeter reads the average value of the product vi = p, where v is the voltage with reference polarity in the ± terminal with respect to the other terminal of the potential coil, and i is the current with reference direction flowing into the ± terminal of the current coil. The wattmeter reads P = ∫₀ᵀ vi dt, which in sinusoidal steady-state reduces to Vᵣₘₛ Iᵣₘₛ cos, where T is the period of p and φ is the angle by which the current lags the voltage.
context_section_description: The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.
  A wattmeter reads the average value of the product v(t)i(t) = p(t), where v(t) is the voltage with reference polarity in the ± terminal with respect to the other terminal of the potential (pressure) coil, and i(t) is the current with reference direction flowing into the ± terminal of the current coil. The wattmeter reads P = (1/T) ∫₀ᵀ v(t)i(t) dt, which in sinusoidal steady-state reduces to Vᵣₘₛ Iᵣₘₛ cos(φ), where T is the period of p(t) and φ is the angle by which the current lags the voltage.
caption: Wattmeter
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