Why Doesn't the Theoretical Power Value Match the Measured Power Value?

Check for differences in the specifications or features of the instruments.

For values that do not match when inputting a 50/60 sine wave

  • Check whether the value is within the specifications (error) of each power meter.
  • Check the DC offset in DC mode
  • Check whether the measuring range is set appropriately.
  • Check whether your power meters have harmonic measurement functions.

If the measuring range is too large relative to the input signal, the amount of error will increase. Differences in measured values can occur due to DC offset and other effects on AC power meters and AC/DC power meters. If the waveform is subtly distorted, harmonic components are present. The effects of such harmonic components can cause differences in measured values between power meters dedicated for 50/60 Hz and power meters supporting harmonics. 

For values do not match when inputting distorted waves or high frequency waves

  • Check whether the value is within the specifications (error) of the high frequency input of each power meter.

If the measured values on power meter A are larger than those from power meter B, there are at least two possibilities:

  1. The frequency characteristic (bandwidth) of power meter A is higher (frequencies are attenuated on power meter B).
  2. Power meter B has superior common mode (voltage) rejection ratio characteristics.

Related Products & Solutions

Precision Power Analyzer WT3000

With 0.02% accuracy and 1MHz bandwidth, the WT3000 delivers where the highest precision measurements are required. It is the industry standard for R&D work on inverters, motor drives, lighting systems and electronic ballasts, UPS systems, aircraft power, transformer testing, and other power conversion devices.

PZ4000 Power Analyzer

The PZ4000 is designed for High Frequency Power Measurements as well as Transient Power Measurements. Its real-time acquisition system can perform cycle-by-cycle power measurements. One to Four input elements offer Basic Power Accuracy of 0.2% with 2 MHz Bandwidth and 5MS/sec digitizing rates.

WT1600 Digital Power Meter

The High-end WT1600 is designed for a wide range of applications, from energy-saving to large load applications. The WT1600 has a six element input capability to provide maximum flexibility, and Basic Power Accuracy of 0.1% with 1 MHz Bandwidth.

WT1800 High Performance Power Analyzer

The WT1800 Power Analyzer offers maximum flexibility with up to six wattmeter elements, high bandwidths, simultaneous high speed digitizing, and wide voltage and current ranges. Although this model is still available, the newer WT1800E offers higher accuracy.

WT2010/WT2030 Digital Power Meters

The WT2000 digital powermeter series has been designed with emphasis on basic performance (bandwidth, accuracy, response speed, and noise immunity) from the viewpoint of measurement of electrical quantities. The broad range of functions of these power analyzers enable them to be used in various fields of applications.

WT500 - Mid Range

  • Power and Harmonic (THD) Measurements with Independent Range Controls
  • Efficiency measurements of AC/DC or DC/AC Inverters & Motors


Power Analyzers and Power Meters

Yokogawa, the world's largest manufacturer of energy and power analyzers and meters, provides a broad choice of digital power analyzers to satisfy all requirements.

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