3.3 Special conditions for safe use
The ATEX intrinsic safety certificate has an ‘X’ suffix
indicating that for some applications special conditions
apply for safe use.
a.
When installed in an Ex px, Ex py or Ex pz panel
enclosure the indicator must be powered by an
appropriately rated Zener barrier or galvanic
isolator located in a safe area.
The supply circuit for indicators used in the
equipment with pressurised type of protection shall
be rated for a prospective short circuit current of
not more than 10kA.
b.
When installed in an Ex e panel enclosure the
indicator must be powered by an appropriately
rated Zener barrier or galvanic isolator located in a
safe area.
c.
When installed in an Ex ta, Ex tb or Ex tc panel
enclosure the indicator must be powered by an
appropriately rated Zener barrier or galvanic
isolator located in a safe area.
d.
For use in Group IIIC conductive dust atmospheres
the indicator shall be mounted such that the
instrument terminals have at least IP6X protection.
3.4 4/20mA input
The input safety parameters for the 4/20mA input,
terminals 1 and 3 are:
Ui
=
30V dc
Ii
=
200mA
Pi
=
0.84W
The maximum equivalent capacitance and inductance
between the two 4/20mA input terminals 1 and 3 is:
Ci
= 13nF
Li
= 8µH (Effectively 0)
The maximum permitted loop cable parameters can
be calculated by adding these figures to Ci and Li of
other instruments in the loop and subtracting the totals
from the maximum cable capacitance Co and cable
inductance Lo permitted for the Zener barrier or
galvanic isolator powering the loop.
Although the indicators do not themselves comply with
the requirements for
simple
apparatus
, the EC-Type
Examination Certificate states that for intrinsic safety
considerations, under fault conditions the output
voltage, current and power at terminals 1 & 3 will not
exceed those specified by clause 5.7 of EN 60079-11
for
simple apparatus.
This simplifies the application
and intrinsic safety documentation for a loop into
which an indicator is connected. Apart from Ci, the
effect of the indicator may be ignored when assessing
the loop safety.
3.5 Intrinsic safety certification label
The intrinsic safety certification label is fitted in a
recess on the top outer surface of the instrument
enclosure. It shows the ATEX certification
information, instrument serial number, year of
manufacture plus BEKA associates' name and
location. IECEx certification information is also
included, a typical label is shown below.
BA307E-SS intrinsic safety certification label
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