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Multimeters - Accuracy, resolution, and sensitivity
The accuracy of a multimeter represents the maximum amount of error that occurs when it takes a measurement. For example, the multimeter may be accurate to 2,000 volts, ±0.8 percent. A 0.8-percent error with the types of voltages used in DC-operated circuits — typically 5 to 12 volts DC — measures only about 0.096 volts. For hobby electronics projects, you don’t need a more precise level of accuracy. As you compare the accuracy of multimeters, bear in mind that just about every model of meter gives the hobbyist the results that he or she needs. Digital meters have another type of rating, this one more commonly called resolution. The number of digits in the display determines the smallest change that the meter can register. Most digital meters designed for hobbyists have 31⁄2 digits, so they can display a value as small as 0.001 (the half digit appears as a 1 on the far left of the display). The hobbyist’s meter can’t accurately represent anything less than 0.001. For most hobby-level electronics projects, you don’tneed to worry about this. Resolution in digital multimeters is also a function of analog-to-digital converter (ADC) electronics. An ADC converts an analog signal to a digital one. Many consumer-grade multimeters use a 12-bit ADC. Without getting into all the technical mumbo-jumbo, a 12-bit ADC can take any analog signal and convert it into 4,096 discrete steps. (These discrete steps are necessary because of the way digital circuits work. In the digital world there can’t be any in-between or “sort of” values.) Meter manufacturers select an ADC with a resolution that works with the number of display digits on the device. A 31⁄2 digit digital readout displays the values of a 12-bit ADC just about right. Along the lines of accuracy and resolution, you need to consider the specification for sensitivity. This phrase means the smallest value that a meter can meaningfully detect when you use it under normal conditions. Quality digital multimeters sport a maximum sensitivity of about 1 microvolt (AC or DC); that’s one millionth of a volt. The lower the value, the better the sensitivity. Quality analog multimeters offer a maximum sensitivity of about 20,000 ohms per volt, typically shown as 20KΩ/V. The higher the ohms value, the better the sensitivity. |
Digital multi-meter
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This intel was contributed by Puniksem
Puniksem
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May, 2012
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