Off

rms" type or it will give wildly erroneous readings. Many inexpensive DMMs do not have the ability to read the peaks of the AC waveform. Reading the peak of the AC waveform is essential for use with engine-powered AC generators.

DC Volts

All DMMs will measure DC volts, and do so accurately. The meter will identify polarity—which wire is positive and which is negative. If the meter is connected backwards (positive to negative and negative to positive), it will indicate this by showing a minus symbol before the number. The polarity feature allows verification that PV modules, inverters, charge controllers, and batteries are properly installed and not reversed in polarity, which often will damage expensive equipment. Checking for correct polarity is an important step when installing systems.

AC Amps

AC amperage is usually measured in two ranges on most DMMs. One range is in the 200 milliamp (mA) scale, and the other usually can measure up to 10 amps. Both ranges are fuse protected, and if you exceed their capability, you will blow the fuse.

Quick Definitions

Voltage is electrical pressure, called EMF (electromotive force) by electronics nerds; the unit used is the volt (V).

Current (or amperage) is the rate of electron flow in a circuit; the unit is the amp (A).

Resistance is the quality of all materials to impede the flow of electrons; the unit is the ohm (Q).

Frequency is the regular reversal in the direction of flow of electrons; the unit is the hertz (Hz).

^wett cc

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