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Power Measurements in Inductive Circuits - Valhalla Scientific Skip to main content

The AC power drawn from the source (e.g. line – 120VAC @ 60Hz 220VAC @ 50Hz) is the integral over one cycle of the instantaneous watts values. As shown in figure C, during a portion of each cycle power is used by the inductive device (e.g. electric motor), while during other portions of the line cycle, power is actually given back by the inductive device. The portion of the cycle where power is given back by the inductive device is called “negative power”. In sinusoidal applications, Power = EI cos θ can be seen in figure C above to reflect the true watts during a complete line cycle (360°).

All Valhalla Digital Power Analyzers can accommodate negative power portions of a circuit’s power curve and perform accurate power measurements regardless of waveform differences between voltage and current. Valhalla’s four-quadrant multiplier design determines instantaneous watts by multiplying voltage and current in real time.

The “instantaneous watts” levels (both positive and negative) are accumulated and the integrated average value (True Watts) is displayed by the power analyzer. The four-quadrant multiplier overcomes problem VA phase offsets, accurately measures power for virtually any non-sinusoidal wave shape and works at low power factors. Valhalla offers a wide variety of digital power analyzers ideally suited for what may be normally a problem power measurement ( i.e. circuit power levels). Low current versions (option 20mA) are available to provide optimized, full-scale resolution and accuracy at lower power levels often associated with modern circuitry.

Valhalla’s Digital Power Analyzers can be an excellent research and development resource for today’s engineers designing the most energy efficient products ever.