Electronics Measurements: What is a Multimeter?
Along with a good soldering iron, a good multimeter is the most important item in your electronics toolbox. Your electronic exploits will be much more fruitful, if you learn how to use it properly.
A simple, inexpensive multimeter can be purchased from your local RadioShack store for under $20. If you shop around, however, you can often find a basic multimeter for under $10 and sometimes for as little as $5.
Of course, you can also spend much more, but if you're just getting started, an inexpensive multimeter is fine. Eventually, you'll want to invest a little more money in a better-quality multimeter.
A digital multimeter displays its values using a digital display that shows the actual numbers for the measurements being taken. The alternative to a digital multimeter is an analog multimeter, which shows its readings by moving a needle across a printed scale. To determine the value of a measurement, you simply read the scale behind the needle.
Alternatively, you can get an analog multimeter where you have to actually read the scale to get the value. Either one is fine so just choose what you are most comfortable with.
The following paragraphs describe the various parts that make up a typical multimeter:
Display or meter: Indicates the value of the measurement being taken. In a digital multimeter, the display is a number that indicates the amperage (current), voltage, or resistance being measured. In an analog meter, the current, voltage, or resistance is indicated by a needle that moves across a printed scale. To read the value, you look straight down at the needle and read the scale printed behind it.
Selector: Most multimeters — digital or analog — have a dial that you can turn to tell the meter what you want to measure. The various settings on this dial indicate not only the type of measurement you want to make (voltage, current, or resistance) but also the range of the expected measurements. The range is indicated by the maximum amount of voltage, current, or resistance that can be measured.
Higher ranges let you measure higher values, but with less precision. For example, the analog multimeter has the following ranges for reading DC voltage: 2.5 V, 10 V, 50 V, 250 V, and 500 V.
If you use the 2.5 V range, you can easily tell differences of a tenth of a volt, such as the difference between 1.6 and 1.7 V. But when the range is set to the 500 V range, you'll be lucky to pick out differences of 10 volts.
On/off switch: Some multimeters don't have an on/off switch. Instead, one of the positions on the selector dial is Off. Other multimeters have a separate on/off switch. If your meter doesn't give you any readings, check to make sure the power switch is turned on.
Test leads: The test leads are a pair of red and black wires with metal probes on their ends. One end of these wires plugs into the meter. You use the other end to connect to the circuits you want to measure. The red lead is positive; the black lead is negative.