Compact power meter offers low current measurement benefits

August 25, 2015 // By Paul Buckley
Yokogawa Meters & Instruments' WT300E series of compact power meters has been released as enhanced versions of Yokogawa's 5th generation of compact power meters, which the company claims to be the world's best-selling power meter.

The family consists of the Models WT310E single phase, WT310EH single phase high current, WT332E two-element and WT333E three-element versions.  The units offer enhanced measurement accuracy of 0.1% of reading +0.05% of range.  The WT310E provides low current measurement capability to 50 µA, and up to 26 ARMS.  The unit is aimed at the engineer doing Stand-by-Power measurements, Energy Star, SPECpower and IEC62301 / EN50564 testing, Battery Charger and other low level power measurements.

Many of today's power conversion circuits use energy saving switching techniques.  These can cause distorted voltage or current waveforms with high harmonic content.  To measure these waveforms accurately, the WT300E series power meters use high resolution sixteen bit ADCs with a digitising rate of 100 ksample/sec.  They have an enhanced low frequency measurement capability of 0.1 Hz.  Overall bandwidth is DC and 0.1 Hz to 100 kHz,

The WT310EH is a single phase high current version with current ranges from 1A to 40 ARMS.  The bandwidth on this model is DC and 0.1 Hz to 20 kHz. The WT332E is a two element meter for use on split phase and three phase three wire circuits.  The WT333E is a three element meter for use on three phase three wire or three phase four wire circuits.  These models have current ranges of 0.5A to 20 ARMS, with low current measurements to 5 mA.  All models have voltage ranges from 15 to 600 Volts RMS, and low voltage measurement capability to 150 mV.

An optional Harmonic Analysis function is available for the WT300E series Digital Power Meters.  This will benefit the design and test engineer in product performance evaluation and for power quality conformance testing.  Both the Normal power parameters and Harmonic data are measured simultaneously providing for faster and more accurate power analysis.  Harmonic Analysis and THD Calculations can be made up to the 50th order from a 50 or 60 Hz fundamental frequency.

The Integration function measures Amp-Hour and Watt-Hour parameters.  This is mportant for stand-by-power measurements.  In the stand-by mode the current can be very low.  Then when the device goes to operation mode, the current can increase substantially. The new Auto Range feature will optimise the range setting for maximum accuracy measurements. Yokogawa's 'Average Active Power' function makes it possible to measure power consumption under conditions where the power fluctuates greatly.  Watt-Hours are measured over some time period then the Time is divided out to leave an average power reading.  This is the industry preferred method for  Stand-by-Power measurements.