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7 I/O MODULES
MELSEC-ST
Circuit example
Method for selecting elements
Remarks
Varistor method
Varistor
Inductive
load
Select a cut voltage (Vc) for
the varistor to meet the
following condition. Multiply the
value by root two for use of AC
power.
Vc Power supply voltage
1.5 (V)
Note that when selecting an
element whose Vc is too high,
its effect will weaken.
The recovery time delays
slightly.
POINT
(1) Avoid providing a protection circuit as shown below.
Capacitor
Inductive
load
This circuit is greatly effective to an arc at shut-off.
However, since an electric charge has been
accumulated in a capacitor while a contact is off,
short circuit current of the capacitor flows while
the contact is on, which tends to result in contact
welding.
Capacitor
Inductive
load
This circuit is greatly effective to an arc at shut-off.
However, since a charge current of the capacitor
flows while the contact is on, which tends to result
in contact welding.
(2) A protection circuit must be provided so that it may be close to a load or contact
(module). If their distance is far, the protection circuit cannot show its effect.
Provide the circuit so that their distance may be within 50cm (19.69 inch) (rough
standard).
Summary of Contents for MELESEC-ST
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