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If I have a 3 and half digital voltmeter operating on the voltage range of 40V then what would be its resolution? While trying to solve this I found in one of the books that only active digits ( which in this case are 3) will be used to calculate the resolution. However doing so I was getting the wrong answer. Is this method not correct?

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3 1/2 digits means the most significant digit can only show a 1 or nothing at all, so the most segments that can be displayed are 1888.

A 40V range would not be able to use the most significant digit, so you only have 3 digits that can be used to display the value, so you can only display up to 40.0

So your least significant digit there represents 100mV (0.1V), which is your resolution.

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3 1/2 DVM can count (0 -1999)

so tatal count is 2000

Range of DVM is 40 V

2000 count =40 v

1 Count - 40÷2000 =0.02 V Is your resolution.

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  • 2
    \$\begingroup\$ Sorry, Vikash, but that's just wrong. The display will have to be on the 200V range rather than 20V, so it will show 40.0V if it's 40V in, so the resolution is 0.1V. Oh, and BTW, a 3-1/2 digit meter can usually go -1999 to 1999 or almost 4000 counts. \$\endgroup\$ – Spehro Pefhany Mar 27 '19 at 1:13

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