34410A/11A/L4411A User’s Guide 119
Measurement Tutorial 4
The fractional NPLC values offer faster measurements, at the expense of some accuracy.
When you set the NPLC to 1 or more, you not only achieve improved accuracy
associated with time averaging, but also achieve rejection of the power–line interference
(normal mode rejection, or NMR); the greater the integral NPLC value, the larger the
NMR.
Aperture is the period, measured in seconds, during which the multimeter's
analog–to–digital (A/D) converter samples the input signal for a measurement. A longer
aperture yields better resolution; a shorter aperture provides for faster measurements.
This feature allows the user to set a specific measurement period, not based on power
line frequency. Values range from 100
μs to 1 s for the 34410A, and from 20 μs to 1 s for
the 34411A/L4411A.
No normal mode rejection is provided in aperture mode.
Offset Compensation
With offset compensation enabled (ON), the multimeter makes a normal temperature
measurement first, followed by a second measurement to determine any offset voltage in
the input circuitry. The resultant displayed measurement corrects for this offset.
Enabling offset compensation increases measurement time.
NULL Reading:
The multimeter allows a separate null setting to be saved for the temperature function.
When making null measurements, each reading is the difference between a stored null
value and the input signal. One application of NULL is to increase accuracy of two–wire
resistance measurements by first nulling the closed–circuit test lead resistance.
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