114 34410A/11A User’s Guide
4 Measurement Tutorial
High-Speed Measurements
Making High–Speed AC Measurements
The multimeter's ac voltage and ac current functions implement three
different low–frequency filters. These filters allow you to trade–off
minimum measured frequency for faster reading speed. The FAST filter
settles in 0.025 seconds, and is useful for frequencies above 200 Hz. The
MEDIUM filter settles in 0.63 seconds for voltage and 0.25 seconds for
current, and is useful for measurements above 20 Hz. The SLOW filter
settles in 2.5 seconds for voltage and 1.67 seconds for current, and is
useful for frequencies above 3 Hz.
With a few precautions, you can perform ac measurements at speeds up to
500 readings per second. Use manual ranging to eliminate autoranging
delays. By setting the trigger delay to 0, the FAST, MEDIUM, and SLOW filters
will allow up to 500, 150, and 50 readings per second, albeit with reduced
accuracy, since the filter may not fully settle. If the sample–to–sample
levels are similar, little settling time is required for each new reading.
Under this specialized condition, the MEDIUM filter will provide reduced
accuracy results at 20 readings per second, and the FAST filter will provide
reduced accuracy results at 200 readings per second.
In applications where sample–to–sample levels vary widely, but the dc
offset level does not change, the MEDIUM filter will settle at 2 to 4 readings
per second (depending upon the lowest frequency component in the
waveform) as shown in the following table:
AC Filter Filter
Bandwidth
Settling Time
(Seconds)
Full Settling
(rdgs/Sec)
Partial
Settling
Maximum
rdgs/Sec
ACV ACI ACV ACI ACV/ACI ACV/ACI
Slow 3 Hz 2.5 1.67 0.4 0.6 2 50
Medium 20 Hz 0.63 0.25 1.6 4 20 150
Fast 200 Hz 0.025 0.025 40 40 200 500
Medium Filter Performance Full Accuracy Reading Rate
No DC Level Change
Lowest Frequency Component 20 Hz 50 Hz 100 Hz 200 Hz
AC Current (allowable rate rdgs/Sec) 44 4 4
AC Voltage (allowable rate rdgs/Sec) 23 4 4
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