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Digital multimeters (DMM), once called voltmeters, have been described as the tape measure for engineers in the new millennium. With electronics and electrical circuits included in almost every consumer and industrial product, DMMs are a must for designing, testing, and troubleshooting. Here’s a look at the features and capabilities of DMMs, as well as how to use them safely.
DMM Basics
DMMs are tools for measuring volts (V), ohms (Ω), and amperes (A). Most DMMs have other features and characteristics, but measuring those three variables are the foundation for all electrical measurements. You should also know the different ways DMMs display their measurements.
Resolution, for instance, refers to how fine a DMM’s measurement is. By knowing the meter’s resolution, you can determine if it is possible for it to see a small change in the measured signal. For example, if the DMM has a resolution of 1 mV on the 4 V range, it can see a change of 1 mV (1/1,000 of a volt) while reading a 1 V signal.
You wouldn’t buy a ruler marked in one-inch (or one-centimeter) segments if you had to measure down to a quarter inch (or one millimeter). A thermometer that measures only in whole degrees isn’t much use when your normal temperature is 98.6 °F. You need a thermometer with one-tenth-degree resolution.
Accuracy is the largest allowable error under specific operating conditions. In other words, it is an indication of how close the DMM’s measurement is to the actual value of the signal. Accuracy for DMMs is usually expressed as a percent of the reading. An accuracy of one percent of reading means that for a displayed reading of 100 V, the actual value of the voltage could be anywhere between 99 V and 101 V.
Digital and analog displays: For high accuracy and resolution, digital display show three or more digits for each measurement. The analog needle display is less accurate and has lower effective resolution because you have to estimate values between the lines. A bar graph shows signal changes and trends just like an analog needle, but is more durable and less prone to damage.
Analog meter specifications are determined by the error at full scale, not...