6) Electrical System Design For Installation In
Hazardous Areas Using Galvanic Isolators
Galvanic isolators although more expensive than Zener
barriers, do not require a high integrity earth connection. For
small systems where a high integrity earth is not already
available, the use of galvanic isolators often reduces the
overall installation cost and simplifies design.
6.1 Single stage alarm
The IS-D105 sounder may be powered by any galvanic
isolator having output parameters within the limits specified in
section 4.3, which has been certified Ex ia by an EC Notified
Body. The sounder may be controlled by turning the galvanic
isolator on and off, or by a mechanically activated switch on
the hazardous area side of the isolator.
Fig 7 Single stage alarm using galvanic isolator.
6.2 Multi stage alarm
The IS-D105 sounder second and third stages may be
activated by using Galvanically Isolated Relays that have
output parameters within the limits specified in section 4.4.
which have been certified Ex ia by an EC Notified Body.
Fig 8 Multi stage alarm using galvanic isolated relays
7) Cable
Parameters
The maximum permitted cable parameters are as specified
on the certificate of the Zener barrier or galvanic isolator that
has been selected for the installation. Normally the limits are
not restrictive, but care should be taken not to exceed a
capacitive limit of 83nF for installations when very long cables
are used.
8) Volume
Control
The output level of the IS-D105 sounder can be set by
adjusting the volume control potentiometer (see Fig 2).
Safe Area
Hazardous Area
+
-
IS-D105 Sounder
Terminals
Galvanic Isolator
Power
Power
-
+
Safe Area
Hazardous Area
Galvanic Isolator
IS-D105 Sounder
Terminals
Galvanic Isolated Relay
-
On/Off*
On/Off*
To a
maximum
of 2 other
sounders
