Keysight E1412A, Руководство пользователя и руководство по программированию SCPI, Страница: 44 / 243

xliv Keysight E1412A Digital Multimeter User Guide
Keysight E1412A Multimeter Application Information AC Current Measurement Errors
AC Current Measurement Errors
Burden voltage errors, which apply to dc current, also apply to ac current
measurements. However, the burden voltage for ac current is larger due to the
multimeter's series inductance and your measurement connections. The burden
voltage increases as the input frequency increases. Some circuits may oscillate
when performing current measurements due to the multimeter's series
inductance and your measurement connections.
Making High-Speed AC Voltage or Current Measurements
The multimeter's ac voltage and ac current functions implement three different
low-frequency filters. These filters allow you to trade low frequency accuracy for
faster reading speed. The
fast filter settles in 0.1 seconds, and is useful for
frequencies above 200Hz. The medium filter settles in 1 second, and is useful for
measurements above 20Hz. The slow filter settles in 7 seconds, and is useful for
frequencies above 3Hz.
With a few precautions, you can perform ac measurements at speeds up to 50
readings per second. Use manual ranging to eliminate autoranging delays. By
setting the preprogrammed settling (trigger) delays to 0, each filter will allow up
to 50 readings per second. However, the measurement might not be very
accurate since the filter is not fully settled. In applications where
sample-to-sample levels vary widely, the medium filter (20Hz) will settle
adequately at almost 1 reading per second, and the fast filter (200Hz) will settle
adequately at almost 10 readings per second.
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 5 readings per second, and the fast filter will provide
reduced accuracy results at 50 readings per second. Additional settling time may
be required when the dc level varies from sample to sample.
DC Blocking Circuitry
The multimeter's dc blocking circuitry has a settling time constant of
0.2 seconds. This time constant 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.