10.3.1 Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output as shown in Fig 12. The
output is polarised and current will only flow in one
direction.
Ron
=
less than 5Ω + 0.7V
Roff
=
greater than 1MΩ
Fig 12 Equivalent circuit of each alarm output
10.3.2 Intrinsic safety
Each alarm output is a separate galvanically
isolated intrinsically safe circuit. The EC-Type
Examination Certificate states that for intrinsic
safety considerations, under fault conditions the
output voltage, current and power at terminals 8 &
9 and 10 & 11 will not exceed those specified by
clause 5.7 of EN 60079-11 for
simple apparatus.
This simplifies system documentation and allows
the alarm output terminals 8 & 9 and 10 & 11 to be
connected to almost any intrinsically safe circuit
protected by a Zener barrier or galvanic isolator
providing the output parameters of the circuit do
not exceed:
Uo =
30V dc
Io
=
200mA
Po =
0.84W
The maximum equivalent capacitance and
inductance between each set of alarm terminals is:
Ci
= 24nF
Li
= 8µH
To determine the maximum permissible cable
parameters these figures should be subtracted
from the maximum permitted cable capacitance
and inductance specified by the certificate for the
interface powering the alarm circuit, such as the
solenoid driver and switch transfer galvanic
isolators shown in Fig 13.
Fig 13 Typical alarm application
(Shown without recommended screened cables)
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