MAN3041-1
18
9
Orbis IS Adaptor
An adaptor is available which enables Orbis detector heads to be fitted to existing Series 60 IS bases in
order to upgrade systems with minimal disruption.
The existing system should conform to ATEX Certificate No. Ex97D2054 SYST. The IS Adaptor is
distinguished by the
markings “part of
intrinsically
safe fire detector Baseefa06ATEX0007X”.
10
System Design
The design of an intrinsically safe fire detection system should only be undertaken by engineers familiar
with codes of practice for detection systems and hazardous area electrical systems. The relevant standards
are BS5839: Part 1, BS EN 60079-14:2003 respectively.
The fire detection performance of the Orbis I.S. range is the same as that of its standard counterparts but
some electrical parameters are different. Please use the technical data given in this guide for Orbis IS
devices. Performance information given in the Orbis Product Guide is applicable to the Orbis I.S. range.
The BASEEFA certification of the I.S. devices covers their characteristics as components of an intrinsically
safe system and indicates that they can be used with a margin of safety in such systems.
10.1
Types of safety barrier
The certified system configurations allow for two types of safety barrier, each of which has its own
advantages and disadvantages. A brief outline of their characteristics is given below.
Single Channel 28V/300
Ω
Barrier
This is the most basic type of barrier and therefore the
lowest in cost. Being passive devices, they also
impose the minimum of restrictions on the operation of the fire detectors. Thus, single channel barriers are
available either as positive or negative polarity where the polarity refers to the polarity of the applied
voltage relative to earth. The significance of this is that one side of the barrier must be connected to a high-
integrity (safety) earth. Although this earth connection has no effect on the operation of Orbis IS devices
and is not needed for their correct operation, it may not be acceptable to the operation of the control and
indicating equipment. If the earth connection is not acceptable then the isolating barriers should be used.
Galvanically Isolated Barrier
Galvanically isolated barriers. These are also referred to
as “transformer isolated d.c. repeaters”, “isol
ating
interfaces” and “transformer isolated current
repeaters”. They differ from conventional shunt zener
barriers in that they provide electrical isolation between the input (safe area) and the output (hazardous
area). This is achieved by the use of a D.C./D.C. converter on the input side which is connected to the
hazardous area through a voltage and power-limiting resistor/ zener combination similar to a conventional
barrier.
The galvanic isolation technique means that the circuit does not need a high integrity (safety) earth and
that the intrinsically safe circuit is fully floating. Earth leakage problems for control and indicating
equipment are therefore eliminated if this type of interface is used.
Note: Although the circuit does not require a high integrity earth, it is permissible to earth either side of the
hazardous area circuit if required by other system considerations.
