Why are the Measured Values for Voltage, Current, and Power Unstable?

Check the "Sync Source" and zero cross filter (frequency filter) settings. For the WT3000, "Sync Source" setting is irrelevant if the data update rate is 250 ms, 500 ms, 1 s, or 2 s.

Sync Source Setting
In principle, if the AC signal is is not averaged over an interval synchronized with the cycle of the signal, a correct measurement cannot be obtained. For the applicable models listed above, the synchronous source determines the interval at which the cycle of the signal is detected and calculated. You should make a determination from the voltage and current waveforms as to whether to set the "Sync Source" to voltage or current.

Detection of the input waveform's period is made using a comparator (zero cross detector) referencing the center of the waveform's amplitude. Be sure to select a waveform for the "Sync Source" that: is nearly sinusoidal, has little harmonic distortion, and that has minimal jitter around the zero cross point (center of the waveform amplitude).

For example, with inverter motors and other such devices, current should be used since it is closer to sinusoidal than voltage which is a PWM waveform, but for commercial frequencies the voltage signal is often an ideal sine wave, so you should select voltage.

For inverters and other such devices, harmonic components are also included in the current, and sometimes the period cannot be detected accurately. In such cases, set the zero cross filter.

The zero cross filter (frequency filter) rejects components equal to or higher than the cutoff frequency, resulting in accurate period detection. The filter cutoff frequency for the WT210, 230, 1600, and PZ4000 is 500 Hz.

Checking the suitability of the "Sync Source" setting
For frequency measurement, check whether the fundamental wave of the item set to the sync source can be accurately measured.

Related Products & Solutions

Mid Range

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


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.

Power Analyzers and Power Meters

Measure characteristics of devices that generate, transform or consume electricity. Also called power meters or wattmeters, these devices measure parameters such as true power (watts), power factor, harmonics, and efficiency.