34410A/11A/L4411A User’s Guide 123
Measurement Tutorial 4
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 susceptible to noise pickup than a
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