BEKA BA334E, Руководство пользователя, Страница: 9 / 64

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If the reset switch is required in the safe area a
Zener barrier or intrinsically safe relay is required to
transfer the contact closure into the hazardous area.
Almost any intrinsically safe relay with certification
permitting the contacts to be connected to
equipment in the hazardous area may be used.
A diode return Zener barrier is not suitable for this
application.
Alternatively the BA334G may be configured so that
the total display is reset to zero when the
&
and
*
push buttons are operated simultaneously for
more than three seconds. See 6.19
3.6 Certification label information
The Rate Totaliser certification information label is
fitted in a recess on the top outer surface of the
enclosure. It shows the ATEX and IECEx
certification information plus BEKA associates
name, location, year of manufacture and the
instrument serial number. Non European
certification information may also be included.
BA334G Certification information label
4. SYSTEM DESIGN FOR GAS HAZARDOUS
AREAS.
4.1 Use with Zener barriers
Zener barriers are the least expensive intrinsically
safe interface between a safe and hazardous area.
However they require a high integrity earth
connection that may be expensive to install and
they do not provide isolation. When a high integrity
earth connection is not already available, it may be
less expensive and complicated to use galvanic
isolators for the installation of a single BA334G.
Terminals 2, 6 and RS2 of the BA334G Rate
Totaliser are internally connected together. If any
of these terminals are earthed, as shown in Figs 2
& 3, the other common terminals should only be
connected to the same earth, i.e. the barrier
busbar, or to circuits that have 500V rms insulation
to earth.
Any Zener barrier may be used with the BA334G
providing it's certification is for use with apparatus
in the required Zone and gas group, and it's output
parameters do not exceed the input parameters of
the Rate Totaliser terminals to which it is
connected. Only one polarity of Zener barrier i.e.
positive or negative, may be used in a Rate
Totaliser system.
Fig 2 illustrates the basic circuit that is used for all
BA334G installations protected by Zener barriers.
For simplicity, connections for the pulse output and
optional alarms and 4/20mA output are shown
separately in sections 6.24 and 10 of this manual.
Fig 2 BA334G used with Zener barriers