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The cabinet is important to improve noise tolerance and suppress noise emissions.
One factor causing the problems is a poor electrical contact between the metal sheets constituting
the cabinet. Generally high frequency noise causes a malfunction in devices, so it is important to
design a cabinet with tolerance to high frequency noise.
(1) Basic structure of the cabinet
Basically, the cabinet must be made of metal.
Welding is recommended for constructing the cabinet because low impedance electrical
conduction is required between the metal sheets of the sidewalls, the roof, and the base of the
cabinet to improve noise tolerance.
Bead welding is better than spot welding as a welding method for the cabinet because it can
provide low impedance electrical conduction between the metal sheets.
When the structure of the cabinet is of assembly type, make sure to keep electrical conduction
by making a direct contact between the metal sheets with their contact areas unpainted.
When the metal sheets of the cabinet need to be connected only with cables because of
structural restrictions, connection at low impedance is difficult as compared with the structure in
which welding is used for connection or a direct connection is made between the metal sheets.
It is necessary to keep a sufficient cross sectional area for the wires to be used, a good contact
between connection points, and a sufficient contact area.
Note) This section describes how to achieve low impedance electrical conduction to improve noise
tolerance. In construction of a protection circuit, a connection between metal sheets is necessary
through electric wires which have the cross section corresponding to the AC input power supply
capacity of the unit installed on each metal sheet.
Establish direct contact between metal sheets
with the joint portions not painted.