22
9.3.1
Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output as shown in Fig 14. 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 14 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
Io
=
200mA
Po
=
0.84W
The
maximum
equivalent
capacitance
and
inductance between each set of alarm terminals is:
Ci
=
0
Li
=
0.008mH (0.01mH)
The maximum allowable cable capacitance will be
the same as that permitted by the certificate for the
device powering the alarm circuit, such as the
solenoid driver or switch transfer galvanic isolators
shown in Fig 15. The maximum permitted cable
inductance will be that specified for the device
powering the alarm circuit less 0.01mH.
Fig 15 Typical alarm application
(Shown without recommended screened cables)
