34410A/11A/L4411A User’s Guide 121
Measurement Tutorial 4
For ac voltage, additional settling time may be required when the dc level varies from
sample to sample. The default sample delays allow for a dc level change of 3% of range
for all filters. If the dc level change exceeds these levels, additional settling time is
required. The multimeter's dc blocking circuitry has a settling time constant of 0.2
seconds. This settling time only affects measurement accuracy when dc offset levels
vary from sample to sample. If maximum measurement speed is desired in a scanning
system, you may want to add an external dc blocking circuit to those channels with
significant dc voltages present. This circuit can be as simple as a resistor and a capacitor.
For ac current, additional settling time is not required when the dc level varies sample to
sample.
Making High–Speed dc and Resistance Measurements
The multimeter incorporates an automatic zero measurement procedure (autozero) to
eliminate internal thermal EMF and bias current errors. Each measurement actually
consists of a measurement of the input terminals followed by a measurement of the
internal offset voltage. The internal offset voltage error is subtracted from the input for
improved accuracy. This compensates for offset voltage changes due to temperature. For
maximum reading speed, turn autozero off. This will more than double your reading
speeds for dc voltage, resistance, and dc current functions. Autozero does not apply to
other measurement functions.
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