Measurements Below Full Scale
You can make the most accurate ac measurements when the multimeter
is at full scale of the selected range. Autoranging occurs at 10% and
120% 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. The accuracy
will be significantly different for these two cases. For highest accuracy,
you should use manual range to get to the lowest range possible for the
measurement.
High-Voltage Self-Heating Errors
If you apply more than 300 Vrms, self-heating will occur 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 will be less than 0.02% and will
dissipate in a few minutes.
Temperature Coefficient and Overload Errors
The Agilent 34401A uses an ac measurement technique that measures
and removes internal offset voltages when you select a different function
or range. If you leave the multimeter in the same range for an extended
period of time, and the ambient temperature changes significantly (or if
the multimeter is not fully warmed up), the internal offsets may change.
This temperature coefficient is typically 0.002% of range per °C and is
automatically removed when you change functions or ranges.
When manual ranging to a new range in an overload conditi on, the
internal offset measurement may be degraded for the selec ted r a nge.
Typically, an additional 0.01% of range error may be introduced.
This additional error is automatically removed when you remove the
overload condition and then chan ge functions or ranges.
Chapter 7 Measurement Tutorial
Measurements Below Full Scale
210