120 34410A/11A/L4411A 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 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 0.625 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 1.66 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 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 provides reduced
accuracy results at 20 readings per second, and the FAST filter provides 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 settles 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) 4 4 4 4
AC Voltage (allowable rate rdgs/Sec) 2 3 4 4
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