Hochiki IFD-E(IS) - Manual (Page 7)

Hochiki Europe (UK) Ltd 7
2-3-0-809/ISS2/JUL07
Galvanically isolated barriers are widely used with conventional flame detector systems. If the system is
of an addressable type with signal pulses on the supply lines then the response time of most standard
barriers will be too slow to allow their use. In these applications special galvanically isolated barriers are
required that can freely transmit the required protocol pulses without introducing severe voltage drops.
These interfaces are available as single or dual channel versions and are recommended for any
application in which direct earth connections are not acceptable.
The galvanically isolated barrier is a two-wire device which does not need an external power supply.
Current drawn from the detector supply connections by the barrier itself is less than 500µA
Approved Safety Barriers
For systems a generic specification for the barriers is as follows:
Any shunt zener diode safety barrier certified and approved to meet the ATEX Directives or CENELEC /
IEC standards.
ATEX group and category II (1) G
CENELEC / IEC marking [EEx ia] II C (associated apparatus)
Having the following or lower output parameters:
Max. output volts U
o
: = 30V
Max. output current I
o
: = 100mA
Max. output power P
o
: = 0.65W
A number of barriers meet this specification and examples are given below:
Supplier Type Polarity Mounting Technique
Pepperl & Fuchs Ltd
77 Ripponden Road
Oldham
Lancashire OL2 8PF
United Kingdom
www.pepperl-fuchs.com Z728
Z779
Z828
KFD0-CS-Ex1.51
KFD0-CS-Ex2.51 +
+
-
DIN rail
DIN rail
DIN rail
DIN rail
DIN rail Shunt 300
Ω
Shunt 300
Ω X 2
Shunt 300
Ω
Galvanic X 1
Galvanic X 2
MTL
Power Court
Luton
Bedfordshire LU1 3JJ
United Lingdom
www.mtl-inst.com MTL7028+
MTL7728+
MTL7779+
MTL7706+ +
+
+
+ DIN rail
DIN rail
DIN rail
DIN rail Shunt 300
Ω
Shunt 300
Ω
Shunt 300
Ω X 2
Active 300
Ω,
4-20mA output
Safety Earth
Single channel and star connected A.C. safety barriers must be connected to a high integrity earth by at
least one and preferably two copper cables, each of cross sectional area of 4mm² or greater. The
connection must be such that the impedance from the connection point to the main power system earth is
less than one ohm.
Intrinsically safe circuits in the hazardous area should be insulated from earth and must be capable of
withstanding a 500V RMS A.C. test voltage for at least one minute.
When using armoured or copper sheathed cables, the armour or sheath is normally isolated from the safe
area busbar.