AFJ Instruments LT32C/10 Руководство по эксплуатации - Страница 15

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D.3 • EUT'S UNDER INSULATION CLASS I

In general, CLASS I devices (power cord with GROUND wire) have good shielding capabilities thanks to

a low-impedance PE (equipotential) protection circuit. In such cases, the earth connection, or PE

conductor of the EUT, can be connected to the reference ground of the test setup.

Since, inside the EUT, the capacitance between the enclosure or Protective Earth terminal, and the

mains conductors is low, at low frequencies the significant component for the test results, is the

symmetric component. Therefore, in such conditions, it may often occur that all conductors show the

same signal level values.

D.4 • EUT'S UNDER INSULATION CLASS II

HANDHELD EQUIPMENT

In all cases where a GROUND wire is missing, the safety accomplishments are met using so-called

"reinforced, or double insulation" design.

When a handle, or grip, made of insulating material, is provided to operate and control the

equipment, the Reference Standards request that the measurements are performed somehow

simulating the influence of the presence of a human hand on the coupling capacitance between the

mains conductors inside the DUT and the enclosure, by wrapping a metal foil around such handle or

grip. The size of the metal foil must be 60mm in width, as long as needed, and connected to the

"Artificial Hand" outlet on the LISN front panel.

If the housing of the device is made of conducting material, a suitable hold point of the housing must

be connected to said outlet.

In case of mixed nature of the housing (partly insulating, partly conducting), the metal foil shall be

wrapped around the insulating part.

Both the metal foil, and the conducting housing, must be connected to the "Artificial Hand" outlet.

NON-HANDHELD EQUIPMENT

Since a GROUND wire is missing, in this case the earth reference is the metal sheet laid on the

measurement table or floor, as specified in the Reference Documents. A suitable metal point on the, if

applicable, non-conducting housing, shall be connected to such reference ground.

Up to frequencies of approximately 3MHz, the coupling between the DUT and the metal sheet is very

low, thus giving rise to possible measurement gross errors, under the influence of external capacitance:

therefore, avoid the proximity of operators, or objects that may be source of such disturbances.

Above 3MHz, the coupling becomes increasingly effective, and external perturbations affect the

measurement to a lesser and lesser extent.

AFJ LT32C/10 LISN - Operating Manual - rev. 3.8 / 2019-01

Distributed by:

Reliant EMC LLC

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