Gonnheimer Elektronic F870S, User Manual

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F870S 2 Pressurized enclosure system F870S Page 9
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2.4.4 Leakage compensation
Within this operation mode the unit generate and hold a pressure level of at lest 0.8 mbar
(80 Pa) inside the Ex p- cabinet.
The use of a proportional solenoid valve prevents wasting of the purge medium while the
pre purging procedure as well later in basic operation mode.
In tradition to the control unit GÖNNHEIMER FS850S, the first Ex p- control unit using pro-
portionally working pressure and flow control, the FS870S works as well as an
input-sided
pressure regulator
:
The proportional solenoid valve is the actuator of a PID- control and regulates the incoming
purge medium accordingly to the leakage of the cabinet. The benefits of pressure feedback
control are:
1. Considerable less consumption of protective gas - additional costs for proportional valve will
be amortized soon
2. Increased service reliability achieved by constant pressure inside enclosure - increasing leak-
age caused by e.g. ageing of the enclosure will be balanced and sudden failure is pre vented
3. Almost no flow noise and only a small protective gas consumption using a solid enclosure
Figure 4: Consumption of protective gas
Another advantage using a proportional solenoid valve is; that pressure control is also used
during purging. A set-point pressure will be achieved in the enclosure, while the flow vol-
ume, that leaves the enclosure, will be recorded and integrated over time, until the required
purge volume is achieved. The advantages are:
1. A defined pressure while purging - pressure sensitive parts of the enclosure, like mem-
brane switch panels or windows, will not be overloaded.
2. Purge volume accuracy is achieved by integration of the purge medium flow volume at
the outlet. Wasting purge medium is no more a topic of today.
The use of the F870S system leads to a considerable stress relief of the Ex p cabinet and
sensitive parts like foil keyboards, windows etc.. In comparison to conventional Ex p- sys-
tems, the FS870S requires a much lower cabinet pressure to achieve a comparable flow
rate. (Example: A reduction of the cabinet pressure by 5 mbar leads to 50 kg / m² de-
creased load at the cabinet walls).