5
This allows the BA324D 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 recorded on a separate label inside the
terminal compartment.
4. SYSTEM DESIGN FOR HAZARDOUS
AREAS
4.1 Transmitter loops
A BA324D 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
BA324D indicator is connected in series with a 2-
wire transmitter protected by a Zener barrier.
Fig 2 BA324D in a transmitter loop
4.2 Remote indication
A BA324D may be driven from a 4/20mA safe area
signal via an intrinsically safe interface to provide a
remote indication within a hazardous area. The
type of interface is not critical, either a Zener
barrier or a galvanic isolator may be used,
providing the output parameters of the interface
are :
Uo less than
30V dc
Io less than
200mA
Po less than
0.85W
Note: when the hazard is a IIC gas, and two single
channel Zener barriers or a two channel Zener
barrier are used, only one barrier or channel may
be a 28V 300ohm device.
Again it is necessary to ensure that the voltage
capability of the 4/20mA signal is sufficient to drive
the indicator plus the voltage drop introduced by
the intrinsically safe interface. Figs 3A, 3B and 3C
show the alternative circuits which may be used.
If one side of the 4/20mA current loop may be
earthed, a single channel Zener barrier provides
the lowest cost protection. If the 4/20mA signal is
not isolated, then two Zener barriers, a two
channel Zener barrier or a galvanic isolator must
be used.
