Introduction to Digital Multimeter Accuracy
Accuracy refers to the maximum allowable error in a specific use environment. In other words, precision is used to indicate
The closeness of the measured value of the digital multimeter to the actual value of the signal under test.
For DMMs, accuracy is usually expressed in percent of reading. For example, the meaning of 1% reading accuracy is: when the display of the digital multimeter is 100.0V, the actual voltage may be between 99.0V and 101.0V.
Specific values may be added to basic precision in specification sheets. Its meaning is the number of words to be added to transform the rightmost end of the display. In the previous example, the precision might be stated as ±(1%+2). Therefore, if the GMM reads 100.0V, the actual voltage will be between 98.8V and 101.2V.
The accuracy of an analog meter is calculated based on the full-scale error, not the displayed reading. Typical accuracy for analog meters is ±2% or ±3% of full scale. Typical basic accuracy of a DMM is between ±(0.7%+1) and ±(0.1%+1) of reading, or even higher.
Introduction to Resistance of Digital Multimeter
Measure the resistance in the electrical barrier. Resistance values vary widely, from a few milliohms (mΩ) for contact resistance to billions of ohms for insulation resistance. Many DMMs measure resistance as low as 0.1 ohms, and some can measure as high as 300 megohms (300,000,000 ohms). For extremely large resistance, the Fluke multimeter will display "OL", indicating that the measured resistance exceeds the range. When measuring an open circuit, "OL" will be displayed.
Resistance measurements must be made with circuit power turned off, or damage to the meter or circuit board will result. Some digital multimeters provide a protection function when a voltage signal is mistakenly connected in resistance mode. Different models of DMMs have different protection capabilities.
When making accurate measurements of low resistances, the resistance of the measuring lead must be subtracted from the measured value. Typical test lead resistance is between 0.2Ω and 0.5Ω. If the resistance of the test leads is greater than 1Ω, the test leads must be replaced.
