Bosch IO-BOX32 Manual page 67

Filter
Voltage drops
1070 072 302-101 (01.06) GB
However, the occurrence of a cable break, pulling put a connector for
inductive load, e. g. solenoid valves, contactors, etc, or the deliberate
deactivation by means of a mechanical contact lead to very high interference
levels which can spread in the system due to galvanic, inductive or
capacitive interaction. To dampen this, a corresponding interference
suppression element (free-wheeling diodes, varistors, RC elements) must
be fitted at the inductive load.
Due to their universal application, it is recommended to use bidirectional
suppressor diodes. These consist either of two opposingly poled, in-line
switched suppressor diodes or one poled suppressor diode with bridge
rectification. Corresponding modules are commercially available.
Also suitable are varistor modules which, for example, are offered by the
manufacturers of contactors for the relevant contactors.
Normally, the interference immunity of the IO-BOX32 is sufficient that a
function is assured even in an environment with relatively strong
interference. To improve the EMC properties even further, it might be
necessary to implement additional filtering measures. These measures are
to be examined for each individual case. Suitable filters can be selected from
the wide range available on the market.
The IO-BOX32 logic supply can bridge voltage drops of up to
10 milliseconds to ensure the continuity of its operation. This means that a
disruption of bus operation by brief voltage drops is unlikely. Drops in supply
at outputs are not covered here. This means that, in the event of voltage
drops of this kind, contactors and other actuators can be de-energized.
Falsified input data due to voltage drops are usually prevented by filters in
the input circuits. The usual activation times are approx. 3 ms. If longer
interruptions in the power supply occur, suitable measures must be initiated.
For example, magnetic voltage stabilizers can be used on the AC voltage
side or stand-by batteries or support capacitors on the DC voltage side.
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