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non-hazardous area hazardous area measuring and control circuit Ex(i)
1’ 1 1 1‘

MT BLITZDUCTOR XT signal line BLITZDUCTOR XT
2’ 2 2 2‘
transmitter
unearthed measuring transformer,
insulation strength A → E: > 500 V a.c.,
with Ex(i) input (max. L o , C o )
L BXT L line L BXT L tr
1’ 1 1 1‘
MT C BXT C line C BXT C tr
2’ 2 2 2‘
C C
≥ L BXT + L line + L BXT + L tr C o ≥ C BXT + C line + C BXT + C tr + C

Figure 8.2.4.1 Calculation of L 0 and C 0

non-hazardous area (safe area) to separate these two differ- Group II is valid for all fields of application, e.g. chemical in-
ent areas. dustry, coal and grain processing, with the exception of under-
The maximum safety values of a safety barrier or a measur- ground mining.
ing transducer with Ex(i) output circuit are defined in the test Group II C has the highest risk of explosion since this group
certificates of an authorised test institute: takes into account a mixture with the lowest ignition energy.
¨ Maximum output voltage U 0 The certification of BLITZDUCTOR for explosion group II C
means that it fulfils the highest, i.e. most sensitive require-
¨ Maximum output current I 0
ments for a mixture of hydrogen in air.
¨ Maximum external inductance L 0
¨ Maximum external capacitance C 0 Classification into temperature classes
When an explosive atmosphere is ignited as a result of the hot
The designer / installer must test in each individual case, surface of a piece of equipment, a substance-specific minimum
whether these permissible maximum values of connected temperature is required to cause an explosion. This ignition
equipment located in the intrinsically safe circuit (i.e. process temperature characterises the ignition behaviour of the gases,
field devices, conductors and SPD) are maintained. The corre- vapours or dusts on a hot surface. For economic reasons, gases
sponding values are printed on the rating plate of the relevant and vapours are therefore classified into certain temperature
equipment or can be found in the type examination certificate. classes. Temperature class T6, for example, specifies that the
maximum surface temperature of the component must not
Note exceed 85 °C during operation or in the event of a fault and
When using intrinsically safe SPDs from DEHN, the internal that the ignition temperature of the gases and vapours must
inductances and capacitances of the equipment are negligi- be higher than 85 °C.
bly small according to the EC type examination certificate. With its T6 classification, BLITZDUCTOR XT also fulfils the high-
Zero must be used here to calculate the maximum values of est requirements in this aspect.
L 0 and C 0 . In accordance with the ATEX / IECEx certificate of conformity,
the following electrical parameters must also be taken into
Classification into explosion groups consideration.
Explosive gases, vapours and mists are classified according to
the spark energy required to ignite the most explosive mixture Selection criteria for SPDs – BLITZDUCTOR XT
with air. Based on the example of BLITZDUCTOR XT, BXT ML4 BD EX 24,
Equipment is classified according to the gases with which it the specific selection criteria for this component are explained
can be used. below (Figures 8.2.4.2).

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