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9.3.1 Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output which as shown in Fig 10.
The output is polarised and current will only flow in
one direction.
Ron
=
less than 5
Ω
+ 0.7V
Roff
=
greater than 1M
Ω
Fig 10 Equivalent circuit of each alarm output
9.3.2 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 (Effectively 0)
To determine the maximum permissible cable
capacitance Ci should be subtracted from the
maximum permitted cable capacitance specified by
the certificate powering the alarm circuit, such as
the solenoid driver and switch transfer galvanic
isolators shown in Fig 11.
Fig 11 Typical alarm application
(Shown without recommended screened cables)