Agilent Technologies U1270 Series Especificaciones descargar pdf (Pagina 8)

Advanced DMM Features

Harmonic ratio

Vsense (voltage sense

detector)

The voltage sense (Vsense), or the non-contact voltage detector, is an important

feature for personal safety. Vsense offers significant protection for any person

that will potentially come in contact with energized electrical components. For

example, Vsense determines the presence of AC voltage in insulated wires, wall

receptacles, fuses, junction boxes, switches, and other voltage-carrying electri-

cal systems without breaking into power lines.

Harmonic distortion has become increasingly prevalent in today’s world due to

the expanded use of equipment and machinery. The harmonic ratio feature can

help technicians quickly check for the presence of harmonics in the electrical

power system. This harmonic ratio function calculates a value from 0 to 100%

to indicate the deviation of non-sinusoidal and sinusoidal waveform. This value

indicates the presence of harmonics. A pure sinusoidal waveform without har-

monics has a harmonic ratio of 0%. Measurements with a higher harmonic ratio

show that more harmonics are present in the signal. The figure below illustrates

how the harmonic ratio is derived.

LPF (low pass filter)

While the trend to replace mechanical systems with electronic systems is

growing, troubleshooting motor drives can be difficult. This is especially true

when taking voltage, frequency, and current measurements on the output side

of the motor drive. A regular true RMS multimeter cannot measure the output

from a motor drive because the variable frequency drive (VFD) applies pulse

width modulated, non-sinusoidal voltage to the motor terminals. Many true RMS

meters display readings 20 to 30% higher than the drive’s controller display as

most of true RMS digital multimeters have wide bandwidth. These multimeters

are measuring the carrier frequency/switching frequency generated by VFDs.

The low pass filter (LPF) is designed to help block unwanted voltages above

1kHz when measuring AC voltage or AC frequency. The LPF can improve mea-

surement performance on composite sine waves that are typically generated by

inverters and variable frequency motor drives.

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Agilent Technologies U1270 Series Especificaciones Pagina 8