Wiring the S7-400
4-20
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
Suppression for DC-Operated Coils
DC-operated coils are interconnected to diodes or zener diodes.
+
-
+
-
With diode With zener diode
Figure 4-7 Suppression for DC-Operated Coils
Suppression with Diodes / Zener Diodes
Suppression with diodes or zener diodes exhibits the following characteristics:
Switching overvoltages can be avoided entirely. A zener diode has a higher
turn-off voltage.
High turn-off delay (6 to 9 times higher than without suppressor circuits)
The zener diode switches off more quickly than a diode circuit.
Suppression with AC-Operated Coils
AC-operated coils are suppressed with varistors or RC elements.
With varistor With RC element
~
~
~
~
Figure 4-8 Suppression with AC-Operated Coils
Suppression with a Varistor
Suppression with a varistor exhibits the following characteristics:
The amplitude of the switching overvoltage is limited but not attenuated.
The steepness of the surge voltage remains the same.
Low turn-off delay.
Suppression with RC Elements
Suppression with an RC element exhibits the following characteristics:
The amplitude and steepness of the switching overvoltage are reduced.
Low turn-off delay.
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