Fluke 28IIEX Fluke 28IIEx User Manual - Page 28

Zero Input Behavior of True-rms Meters, Low-Pass Filter, AC current: below 3 % of 600

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28 II Ex Users Manual When you measure voltage, the Product puts approximately 10-MΩ (10,000,000 Ω) impedance in parallel with the circuit. This loading effect can cause measurement errors in high-impedance circuits. In most cases, the error is negligible (0.1 % or less) if the circuit impedance is 10 kΩ (10,000 Ω) or less. For better accuracy when you measure the dc offset of an ac voltage, measure the ac voltage first. Record the ac voltage range, then manually select a dc voltage range equal to or higher than the ac range. This procedure has better accuracy of the dc measurement because the input protection circuits are disabled. Zero Input Behavior of True-rms Meters True-rms meters accurately measure distorted waveforms, but when the input leads are shorted together in the ac functions, the Product shows a measurement between 1 and 30 counts. When the test leads are open, the measurements can change from interference. These offset measurements are common. They do not change the ac measurement accuracy of the Product for the specified measurement ranges. Unspecified input levels are: • AC voltage: below 3 % of 600 mV ac, or 18 mV ac • AC current: below 3 % of 60 mA ac, or 1.8 mA ac • AC current: below 3 % of 600 μA ac, or 18 μA ac 18 Low-Pass Filter The Product is has an ac low-pass filter. When you measure ac voltage or ac frequency, push  to set the low-pass filter mode (K). The Product measures in the chosen mode, but the signal diverts through a filter that stops unwanted voltages more than 1 kHz, refer to Figure 3. The lower frequency voltages go through with decreased accuracy to the measurement less than 1 kHz. The low-pass filter can get you better measurement performance on composite sine waves that are typically found on inverters and variable-frequency motor drives.

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28 II Ex
Users Manual
18
When you measure voltage, the Product puts
approximately 10-M
Ω
(10,000,000
Ω
) impedance in
parallel with the circuit. This loading effect can cause
measurement errors in high-impedance circuits. In most
cases, the error is negligible (0.1 % or less) if the circuit
impedance is 10 k
Ω
(10,000
Ω
) or less.
For better accuracy when you measure the dc offset of an
ac voltage, measure the ac voltage first. Record the ac
voltage range, then manually select a dc voltage range
equal to or higher than the ac range. This procedure has
better accuracy of the dc measurement because the input
protection circuits are disabled.
Zero Input Behavior of True-rms Meters
True-rms meters accurately measure distorted
waveforms, but when the input leads are shorted together
in the ac functions, the Product shows a measurement
between 1 and 30 counts. When the test leads are open,
the measurements can change from interference. These
offset measurements are common. They do not change
the ac measurement accuracy of the Product for the
specified measurement ranges.
Unspecified input levels are:
•
AC voltage: below 3 % of 600 mV ac, or 18 mV ac
•
AC current: below 3 % of 60 mA ac, or 1.8 mA ac
•
AC current: below 3 % of 600
μ
A ac, or 18
μ
A ac
Low-Pass Filter
The Product is has an ac low-pass filter. When you
measure ac voltage or ac frequency, push
to set
the low-pass filter mode (
K
). The Product measures in
the chosen mode, but the signal diverts through a filter
that stops unwanted voltages more than 1 kHz, refer to
Figure 3. The lower frequency voltages go through with
decreased accuracy to the measurement less than 1 kHz.
The low-pass filter can get you better measurement
performance on composite sine waves that are typically
found on inverters and variable-frequency motor drives.