Fluke, Scopemeter, a combination of multimeter and scope, also checks harmonic magnitude

The trend in home appliances is to make them smaller, lighter, and more efficient. How can we reduce power consumption and increase efficiency?

The core and differentiating factor in home appliances is the motor. The conventional fixed-speed motor always runs at the same speed when electricity is supplied and requires a constant level of electricity to be continuously supplied. As such, it is vulnerable to voltage changes and consumes a lot of power.

The motor technology to solve this problem is to incorporate an inverter. An inverter, which converts direct current into alternating current, can have a voltage and frequency of the desired size when converting into alternating current. If an inverter is incorporated into a motor, the rotation speed of the motor can be adjusted according to the amount of energy required, allowing control of speed and efficiency.

Using an inverter has the advantage of allowing gear changes without a separate gearbox, reducing starting current, and controlling multiple motors with one inverter. However, it has the disadvantage of generating harmonics.

Harmonics occur when multiples of the fundamental waveform are superimposed on the fundamental waveform, causing distortion of the fundamental waveform and resulting in voltage imbalance. This can have a detrimental effect on the entire motor drive system and can even result in motor damage. The causes of harmonics are varied, but they are mainly caused by a rapidly increasing electronic load.

In motor drive systems, it is necessary to measure the values at the input to ensure that the drive does not generate harmonics or create voltage dips, swells, or transients that could interfere with other electrical operations.

Fluke's power measuring instrument, the FLUKE 430 series, can analyze all elements of power, including voltage, current, frequency, power, harmonics, transients, and voltage dips/swells, all at once with a single device. You can check for unusual phenomena by simply entering the nominal voltage without any special settings.

Voltage imbalance, which is the voltage level difference at each phase, can be measured by measuring the voltage difference between the input and output terminals. There is a difference in whether the measured waveform is a sine wave or a pulse width modulation waveform. In the case of the output terminal, a pulse width modulation signal (PWM) is output. This is created by adjusting the pulse waveform to various frequencies to create a waveform with a value similar to an actual sine wave. The frequency varies depending on the inverter characteristics, but is usually Hz to MHz (GHz). Since general power analyzers are set to the operating frequency of 50 Hz and 60 Hz, measurement is impossible, so a scope meter with a wide frequency bandwidth must be used for measurement.

Scopemeter is a combination of millimeter and oscilloscope functions, and Fluke's Fluke190 series is a representative example. It is a 2 or 4-channel portable instrument that includes a DMM function that can test voltage, resistance, and diodes using a 4mm banana input terminal, just like a general multimeter. The maximum resolution is 500 counts, and it is equipped with a lithium-ion battery, allowing up to 8 hours of use. It is specialized for industrial sites and has a safety rating of CATIII 1000V and CATIV 600V.

Fluke Baek Jun-ho, the manager, said, “Basically, a THD of 6% or more is a problem. Using a power meter, you can check not only THD but also the size of each harmonic order,” and “Since the symptoms and causes are different for each order, it is important to identify the harmonic content of each order.”