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Digital Multimeter Frequently Asked Questions


Q: Why does my multimeter not go to zero in the ac volts mode?
A: If it is a true-rms ac multimeter, such as the 17X or 8X, it will not zero and should not be zeroed. Most of these true-rms type multimeters have a minimum ac voltage and current level specification for both the ac volts and ac current modes, typically specified from 3% to 5% of range. When a signal is applied above the specified minimum level, the meter will meet its accuracy specifications. You will find this specification in the specification section in the rear of the user manual.
Q: What does the CAT III safety rating mean?
A: The answer is in the application note "ABCs of DMMs Multimeter features and functions explained".
Q: In the accuracy specification (1% of reading + 3 counts), what does the counts mean?
A: It refers to the least significant digit on the meter on that range. As an example, lets work the math for measuring 120 volts ac on this 6000 count meter (the A to D converter goes from 0 to 5999 counts). To measure 120 volts ac, the meter will have to be on the 600.0 ac voltage range. The resolution (least significant digit) then is 0.1 volt. (120 V X 1% = 1.2 V + 3 digits) = (1.2 V + 0.3 v) = 1.5 V
Q: What is the difference in the Min/Max and Peak modes on multimeters?
A: The Min/Max mode is as its name implies, it is the highest and lowest reading that the multimeter measured from the time the Min/Max record mode was started. Typically, they need the measured signal's maximum or minimum to be 200 to 350 milliseconds long or longer to get an accurate reading. They work from any mode such as volts dc, true-rms volts ac, resistance, and current functions. Peak mode measures the positive and negative peak voltage of a signal. For the 120 volt ac line, the peaks will read +169 volts and -169 volts (120 V x 1.414 = 169 V for a clean sine wave). Typically they will work for peaks that are 250 microseconds or longer.
Q: When I short my test leads together in the resistance mode, it does not read zero. Why not?
A: The meter is measuring the resistance of the test leads, which for a new set of test leads will typically be in the 0.1 to 0.3 ohm range. The test lead error needs to be subtracted from the resistance readings. Some of the more feature rich meters will have a Relative delta (use the actual delta symbol in the final article) mode pushbutton that will subtract the lead error for you.
Q: How many save readings for the Fluke 289 can be stored in the meter?
A: You may save up to 400 total saved single readings in the Save Memory.
Q: How many record sessions for the Fluke 289 can be saved before download in necessary?
A: You may save up to 400 total recordings in memory. With intervals set to 15 minutes, you could get several one week recordings before it is necessary to upload results to a computer, even if you had used all of 400 of the saved reading memory locations.
Q: For the Fluke 289, how many Min/Max and Peak readings can be saved in meter memory?
A: Again, the total possible in each (Min/Max or Peak) is 400, for a total of 800 readings.
Q: For the Fluke 289, what about the file folders in the +Name menu. Can these also store 400 readings each?
A: No. When you select names, such as Motor, Panel, Circuit, Control, or Battery, what you are doing is placing Save, Record, Min Max or Peak readings in the chosen file folder. The total available in each measurement type is still 400.

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