Interpreting Multimeter Specifications
This section is provided to give you a better understanding of the terminology
used and will help you interpret the multimeter’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 Agilent 34401A can measure 9.99999 Vdc on the 10 V
range. This represents six full digits of resolution. The multimeter 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 multimeter can detect for a
given measurement. Sensitivity defines the ability of the multimeter 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
Agilent 34401A, these functions are specified to measure down to 1% of
the selected range. For example, the multimeter can measure down to
1 mV on the 100 mV range.
Chapter 8 Specifications
Interpreting Multimeter Specifications
226
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