120 34410A/11A/L4411A User’s Guide
4 Measurement Tutorial
Measurements Below Full Scale
You can make the most accurate ac measurements when the multimeter is at
or near the full scale of the selected range. Autoranging occurs at 10%
(down–range) and 120% (up–range) of full scale. This enables you to measure
some inputs at full scale on one range and 10% of full scale on the next higher
range. In general, the accuracy is better on the lower range; for the highest
accuracy, select the lowest manual range possible for the measurement.
High–Voltage Self–Heating Errors
If you apply more than 300 V
rms
, self–heating occurs in the multimeter's
internal signal–conditioning components. These errors are included in the
multimeter's specifications.
Temperature changes inside the multimeter due to self–heating may cause
additional error on other ac voltage ranges. The additional error is less than
0.02% and dissipates in a few minutes.
AC Current Measurement Errors (Burden Voltage)
Burden voltage errors, which apply to dc current, also apply to ac current
measurements. However, the burden voltage for ac current is larger due to the
multimeter's series inductance and your measurement connections. The
burden voltage increases as the input frequency increases. Some circuits may
oscillate when performing current measurements due to the multimeter's
series inductance and your measurement connections.
Low–Level Measurement Errors
When measuring ac voltages less than 100 mV, be aware that these
measurements are especially susceptible to errors introduced by extraneous
noise sources. An exposed test lead acts as an antenna and a properly
functioning multimeter will measure the signals received. The entire
measurement path, including the power line, act as a loop antenna. Circulating
currents in the loop create error voltages across any impedances in series with
the multimeter's input. For this reason, you should apply low–level ac voltages
to the multimeter through shielded cables. You should connect the shield to
the input LO terminal.
Make sure the multimeter and the ac source are connected to the same
electrical outlet whenever possible. You should also minimize the area of any
ground loops that cannot be avoided. A high–impedance source is more
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