3 Features and Functions
70 Keysight 34420A User’s Guide
Digital Filter
– The digital filter is a moving average (boxcar) filter. Equal weighting is applied
to all readings to calculate the displayed reading.
– Three digital filters are available:
SLOW (average last 100 readings),
MEDIUM (average last 50 readings), or
FAST (average last 10 readings)
– When the digital filter is enabled, the ‘Filt’ annunciator flashes until the
required number of readings are obtained. The measurement displayed before
the ‘Filt’ annunciator is steady is the average of the number of readings taken
so far. For example, with the filter set to MEDIUM (average of 50 readings), the
measurement displayed after 20 readings will be the average those 20
readings. The ‘Filt’ annunciator will flash until 50 readings have been taken.
– The filter count resets (and the ‘Filt’ annunciator will flash) if the function,
range, integration time, or channel is changed.
– The filter count resets if a reading is outside a set range of the average. The
amount of input reading change required to reset the filter count is:
Analog Filter
The analog filter is an 11 Hz, two-pole low pass filter. Use this filter to remove line
frequency noise from the input measurement.
– The filter requires approximately 300 milliseconds after the input is present to
settle. Using the filter, therefore, slows the measurement rate significantly.
– Use the analog filter only when line power noise (50/60 Hz) is causing an
overload (OVLD) condition. See page 77.
– The analog filter is available for voltage and thermocouple temperature
measurements. The analog filter is not available for resistance measurements.
1mV Range All Other Ranges
FAST ± 400 ppm of range ± 100 ppm of range
MEDIUM ± 700 ppm of range ± 300 ppm of range
SLOW ± 2000 ppm of range ± 1000 ppm of range
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