KYORITSU 2417 - Manual (Page 15)

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Frequency response of 40 Hz to 1 kHz permits measurements
of current with harmonics superimposed on the fundamental
frequency. High frequency current from appliances such as
inverters, switching regulators etc. can therefore be measured.
NOTE
● Model 2417 hasa very good frequency response due to
the electrical property of the transformer jaws used for the
instruments.
Therefore, it measures AC current of not only 50 Hz or 60 Hz
fundamental wave form but also of higher frequencies and
harmonics superimposed on the fundamental frequency
when present in the circuit under test. To eliminate the effect
of noise from the high frequency and measure AC current
of 50 Hz or 60 Hz fundamental frequency, a filter circuit is
incorporated into the Model 2417 which works when the
frequency selector switch is set to the 50/60 Hz position.
It is designed to attenuate frequencies starting from around
100 Hz with an attenuation characteristic of approx. -24
dB/octave (signal strength declines to one sixteenth of that
at the initial frequency when it doubled). Recently there
has been increased usage of power through inverters,
switching regulators, etc. When the high frequency noise
from such appliances leaks or flows into the ground through
capacitors not filtering completely, the earth leakage breaker
may not trip. In such a case the instruments may not give
current readings with the frequency selector switch at the
50/60 Hz position. Therefore, it is necessary to make current
measurements with the switch at the "WIDE" position.
When in doubt as to the presence of high frequencies
and harmonics that affect AC current measurements,
take current readings with the switch at the 50/60 Hz and
"WIDE" positions respectively and then compare the results
obtained.