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Interpreting Internal DMM Specifications
This section is provided to give you a better understanding of the
terminology used and will help you interpret the internal
DMM’s
specifications.
Number of Digits and Overrange
The “number of digits” specification is the most fundamental, and
sometimes, the most confusing characteristic of a multimeter.
The number of digits is equal to the maximum number of “9’s” the
multimeter can measure or display. This indicates the number of
full digits. Most multimeters have the ability to overrange and add
a partial or “
1
⁄
2
” digit.
For example, the internal
DMM can measure 9.99999 Vdc on the 10 V
range. This represents six full digits of resolution. The internal
DMM
can also overrange on the 10 V range and measure up to a maximum of
12.00000 Vdc. This corresponds to a 6
1
⁄
2
-digit measurement with 20%
overrange capability.
Sensitivity
Sensitivity is the minimum level that the internal DMM can detect for a
given measurement. Sensitivity defines the ability of the internal
DMM
to respond to small changes in the input level. For example, suppose you
are monitoring a 1 mVdc signal and you want to adjust the level to
within
±1 µV. To be able to respond to an adjustment this small, this
measurement would require a multimeter with a sensitivity of at least
1
µV. You could use a 6
1
⁄
2
-digit multimeter if it has a 1 Vdc or smaller
range. You could also use a 4
1
⁄
2
-digit multimeter with a 10 mVdc range.
For ac voltage and ac current measurements, note that the smallest
value that can be measured is different from the sensitivity. For the
internal
DMM, these functions are specified to measure down to 1% of
the selected range. For example, the internal
DMM can measure down
to 1 mV on the 100 mV range.
Chapter 9 Specifications
Interpreting Internal DMM Specifications
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