4
Although the BA304D indicator does not itself
comply with the requirements for
simple
apparatus
,
the EC-Type Examination Certificate specifies that
under fault conditions the voltage, current and
power at the 4/20mA input terminals 1 and 3 will
not exceed those specified for
simple apparatus
in
Clause 5.4 of EN50020:1994. This allows the
BA304D to be connected into any intrinsically safe
circuit protected by a Zener barrier or galvanic
isolator providing the output parameters of the
circuit do not exceed:
Uo
=
30V dc
Io
=
200mA
Po
=
0.85W
For this reason the BA304D indicator has only an
apparatus certificate. No system certificate has
been issued, or is required, because the system
certificate of the loop into which the indicator is
connected remains valid. Note: The optional
display backlight does have a system certificate.
The BA304D EC-Type Examination Certificate
specifies the maximum equivalent capacitance and
inductance between the two 4/20mA input
terminals is:
Ci
=
20nF
Li
=
10µH
To determine the maximum permissible cable
parameters these figures must be subtracted from
the maximum cable capacitance and inductance
permitted by the system certificate of the loop into
which the BA304D is installed.
3.3 Zones, gas groups and T rating
The BA304D has been certified for Group II,
Category 1, G, EEx ia IIC T5 Tamb -40 to 60
o
C.
When connected to a suitable system the indicator
may be installed in:
Zone
0
explosive gas air mixture
continuously present.
Zone 1
explosive gas air mixture likely
to occur in normal operation.
Zone 2
explosive gas air mixture not
likely to occur, and if it does will
only exist for a short time.
Be used with gases in groups:
Group
A
propane
Group
B
ethylene
Group
C
hydrogen
Having a temperature classification of:
T1
450°C
T2
300°C
T3
200°C
T4
135°C
T5
100°C
This allows the BA304D indicators to be installed
in all Zones and to be used with most common
industrial gases.
3.4 Certification Label Information
The certification label is fitted in a recess on the
top outer surface of the enclosure. It shows the
ATEX certification information plus BEKA
associates name and location. Non European
certification information may also be included. The
instrument serial number and date of manufacture
are shown on a separate label inside the terminal
compartment.
4. SYSTEM DESIGN FOR HAZARDOUS
AREAS
4.1 Transmitter loops
A BA304D indicator may be connected in series
with almost any intrinsically safe 4/20mA current
loop and calibrated to display the measured
variable or control signal in engineering units.
There are two basic design requirements:
1. The intrinsic safety output parameters of the
4/20mA loop, which are defined by the Zener
barrier or galvanic isolator, must be less
than:
Uo
=
30V dc
Io
=
200mA
Po
=
0.85W
2.
The loop must be able to tolerate the
additional 1.1V required to operate the
indicator.
Fig 2 illustrates a typical application in which a
BA304D indicator is connected in series with a 2-
wire transmitter protected by a Zener barrier.
