Figure 3-58: Circuit With A Diode (Ac/Dc Operation) - Siemens sirius System Manual

Diode
Surge suppressors
SIRIUS System Manual
GWA 4NEB 430 0999-02b
Circuit with diode
(DC operation)
U [ V ]
Sp
20
0
0 200

Figure 3-58: Circuit with a diode (AC/DC operation)

This is what happens when a coil is disconnected that is connected to a
diode:
Advantages: No overvoltage occurs during disconnection. The diode block
becomes effective at 0.6 V.
Disadvantage: The diode can only be used for DC operation.
The break time of the contactor is considerably increased and amounts to 6
to 9 times the off-delay.
This increased break time can be used, if necessary, for control purposes,
such as for bridging brief interruptions in voltage.
Zener diodes (diode combinations) are available for shorter break times. The
break time then amounts to 2 to 6 times the off-delay.
The following surge suppressors are available for the 3RT1 contactors:
Surge suppressor
Suppression diode
Diode combination:
suppression diode and Zener
diode
Varistor
RC element
Table 3-28: Surge suppressor
U
Sp
^
= 0, 6 V = U
SP
der D i ode
t [ µs ]
With LED
For S00 For S00
x x
-- x
x x
-- x
3RT1/3RH1 contactors
Without
LED
For S0 For S2, S3
-- --
x x
x x
x x
3-75