B&R BRCOMP1-0 Anwenderhandbuch Seite 152

B&R COMPACT PLC
If the coil resistance is less than 24 Ω, the thermal protection unit takes over and switches the output
off.
At a coil resistance of between 24 Ω and 48 Ω the switch-on tiem should be paid attention to. Depend-
ing on the switching frequency, it may not be longer than 10 seconds or not longer than the switch-off
time. Continued operation is not possible in this range!
If, for example, one switching cycle per second is executed, the switch-on time may not be longer than
0.5 sec.
Example With which maximum switching frequency can a magnetic valve be switched with the
following coil data?
Find your coil resistance on the Y axis and follow the horizontal line to the right until
you reach the intersecting parameter curve for 2 H (see diagram). At this intersection
the vertical line to the x axis can be found. Follow this line to the x axis and read the
maximum switching frequency (pay attention to the logarithmic scale).
The magnetic valve can be operated at a maximum switching frequency of 4 Hz.
Operation with a higher switching frequency is not allowed and can lead to a thermal
shutdown of the output.
If a higher switching frequency is required, an external protection circuit must be
implemented. Most manufacturers of relays and magnetic valves provide protective
circuits for the respective elements.
The inverse voltage V
Example of a protection circuit
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Inductivity:
Coil resistance:
must be ≤ 8 V.
F
V
F
2 H
120 Ω
Relay