User`s guide

34410A/11A/L4411A User’s Guide 117
Measurement Tutorial 4
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) 44 4 4
AC Voltage (allowable rate rdgs/Sec) 23 4 4
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