Hioki IM7580, Instruction Manual

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Countermeasures to Prevent Entry of External Noise
Appx. 2 Countermeasures to Prevent Entry of
External Noise
This instrument has been designed not to malfunction even when there is entry of noise due to the
measurement cables and the power supply line.
However, measurement errors or malfunctions can result in case of significantly high levels of
interference. Refer to the examples given below for countermeasures that can be taken with
respect to noise in case of a malfunction.
Countermeasures to prevent entry of noise from the power supply line
You can use the following countermeasures to reduce the entry of noise from the power supply line.
Grounding using a protective ground wire
This instrument has been provided with a structure such that the ground wire of the power cable
can be used as protective grounding for the instrument.
Protective grounding plays an important role in not only the prevention of electrical accidents but
also the use of an internal filter to eliminate the entry of noise from the power supply line.
Use the supplied 2-pole grounding type power cord, and connect to a commercial power supply
with a ground wire that has been grounded without fail.
Attaching a noise filter to the power supply line
Connect a commercial plug-in noise filter to the power outlet and connect the instrument to the
output of the noise filter in order to suppress the entry of noise from the power line.
Plug-in noise filters are commercially available from various manufacturers.
Inserting an EMI suppression ferrite core to the power cord
Pass the power cord through a commercially available EMI suppression ferrite core and secure the
core as close as possible to the AC power inlet of the instrument in order to suppress the entry of
noise from the power supply line.
Suppression is more effective if the EMI suppression ferrite core is attached close to the power plug
of the power supply.
If a toroidal ferrite core or split ferrite core with sufficiently large internal diameter is used, the
amount of noise suppression can be increased by passing the power cord through the core several
times. EMI ferrite cores and ferrite beads are commercially available from various specialist
manufacturers.
Countermeasures to prevent entry noise from the measurement
cables
If interference is producing noise in the measurement cables, its influence can be moderated by the
following countermeasure.
Attaching an EMI suppression ferrite core to commercially available cables
Pass the test cables through a commercially available anti-interference ferrite core, and fix it close
to the measurement terminals, this will suppress noise from the measurement cables.
Moreover, if there is margin in the internal diameter of the ferrite core, the amount of noise can be
further reduced by winding the measurement cables several times around the ferrite core (as with
the power cord as described above).
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