BEKA BA377NE, Руководство пользователя

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3.4.2 Ex nA certification
Each control output is a separate galvanically
isolated Ex nA circuit with the following input
parameters:
Ui = 30V dc
Ii = 200mA
This allows each control output to switch any dc
circuit providing that in normal operation the
maximum supply voltage is not greater than 30V dc
and the switched current is not greater than 200mA.
Providing that the BA377NE Timer or Clock is
correctly installed in a panel enclosure located in
Zone 2 complying with the requirements for Ex n
protection, the two control outputs may be used to
switch suitably protected equipment located in any
Zone of a hazardous area, or equipment located in a
safe area.
Fig 6 shows a typical application in which a
BA377NE Timer or Clock, mounted in an Ex n panel
enclosure located in Zone 2, is being controlled by a
flameproof Ex d 2-wire sensor located in Zone 1.
Control output 1 is switching an Ex e sounder in
Zone 1 and control output 2 is switching a sounder
located in the safe area.
Fig 6 Typical control output application
(Shown without recommended screened cables)
To comply with the requirements of EN 60079-14
Electrical installations design, selection and
erection , each of the wires entering the hazardous
area should be individually fused and contain a
means of isolation. These two requirements are
frequently satisfied by using fuse holders with easily
removable fuses and removing the fuses to achieve
isolation. This is a satisfactory method at the low
voltages and currents common in instrumentation
systems. Clear identification of, and easy access to
the means of isolation is essential for their effective
use. It is also necessary to ensure that the
maintenance
procedure makes sure that
unauthorised re-closure of the switches does not
occur. It is not considered necessary to have a
means of isolation or electrical protection for the
screen. Figure 2 illustrates an example of this type
of fused terminal block.
For some application Ex nA instrumentation
energised by a current limited power supply or
instrument that can be switched off, is often
considered adequate and to comply with the
requirements of the standard.