Zero input behavior of true rms meters (87), Low pass filter (87) – Fluke 87 V User Manual

Page 23

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Making Measurements


Zero Input Behavior of True RMS Meters (87)

True Rms Meters accurately measure distorted
waveforms, but when the input leads are shorted together
in the AC functions, the meter displays a residual reading
between 1 and 30 counts. When the test leads are open,
the display readings may fluctuate due to interference.
These offset readings are normal. They do not affect the
Meter’s AC measurement accuracy over 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


A AC, or 18



Low Pass Filter (87)

The 87 is equipped with an ac low pass filter. When
measuring ac voltage or ac frequency, press A to
activate the low pass filter mode (K). The Meter continues
measuring in the chosen ac mode, but now the signal
diverts through a filter that blocks unwanted voltages above
1 kHz, refer to Figure 3. The lower frequency voltages pass
with reduced accuracy to the measurement below 1 kHz.
The low pass filter can improve measurement performance
on composite sine waves that are typically generated by
inverters and variable frequency motor drives.



To avoid possible electric shock or personal
injury, do not use the Low Pass Filter option
to verify the presence of hazardous voltages.
Voltages greater than what is indicated may
be present. First, make a voltage measure-
ment without the filter to detect the possible
presence of hazardous voltage. Then, select
the filter function.


In Low Pass Mode, the Meter goes to manual
mode. Select ranges by pressing the RANGE
button. Autoranging is not available in Low Pass

1 kHz

100 Hz


Figure 3. Low Pass Filter

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