10.3.1 Solid state output
Each alarm output is a galvanically isolated single
pole solid state switch as shown in Fig 11. The
output is polarised and current will only flow in one
direction, terminals 8 and 10 should therefore be
connected to the positive side of the circuit being
switched.
Ron
=
less than 5
Ω
+ 0.7V
Roff
=
greater than 1M
Ω
Fig 11 Equivalent circuit of each alarm output
10.3.2 Type nA certification
Each alarm output is a separate galvanically isolated
Ex nA circuit with the following input parameters:
Ui
=
30V dc
Ii
=
200mA
This allows each alarm output to switch any dc
circuit providing that in normal operation the
maximum supply voltage is not greater than 30V and
the switched current is not greater than 200mA.
Fig 12 shows a typical application in which a
BA354NE Rate Totaliser is displaying the output
from a 2-wire transmitter in Zone 2. Alarm 1 is
switching a solenoid valve in Zone 2 and alarm 2 is
switching a sounder located in the safe area.
The BA354NE has Ex nA protection but when
mounted in Zone 2 the alarm outputs may be used
to switch Ex nC Protected Sparking and Ex nR
Restricted Breathing apparatus in addition to Ex nA
apparatus.
Fig 12 Typical alarm application
(Shown without recommended screened cables)
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