6
4. SYSTEM DESIGN FOR GAS HAZARDOUS
AREAS.
These indicators are versatile and simple to apply,
allowing them to be safely connected to hazardous
area equipment employing any type of certified
explosion protection such as, flameproof Ex d,
pressurised Ex p, increased safety Ex e or Ex nA.
They should not be used with energy limited
protected equipment such as intrinsic safety Ex i or
Ex nL.
4.1 Transmitter loops
The BA304SG and BA324SG may be connected in
series with almost any hazardous area Zone 1 or
Zone 2 4/20mA loop. They can be configured and
calibrated on-site to display a measured variable
or control signal in engineering units.
The
indicators are transparent to HART
®
signals.
There are three simple design requirements:
1. The loop must be able to tolerate the
additional 5.3V required to operate the
indicator.
When fitted with an optional
backlight this increases to 9.1V
2. The 4/20mA loop supply voltage must not
exceed 30V.
3. The indicator should be fitted with Ex e
certified cable glands and / or stopping plug.
4. Wiring should comply with the requirements
of
IEC 60079-14
Electrical
installations
design, selection and erection.
Figs 2 illustrates a typical application in which an
indicator is connected in series with a 2-wire
flameproof Ex d transmitter.
Alternatively an
increased safety Ex e, pressurised Ex p, or in Zone
2, a Type n Ex nA transmitter could be used.
Fig 2 Typical application showing indicator
displaying transmitter output.
4.2
Remote indication
Both models may be driven from a safe area
instrument with a 4/20mA output to provide a
remote display within a Zone 1 or 2 hazardous
area as shown in Fig 3.
Fig 3 Remote indication in Zone 1 or 2
4.3
Monitoring hazardous area equipment
The BA304SG and the BA324SG also provide a
convenient way of monitoring a 4/20mA process
variable in hazardous area equipment protected by
a flameproof Ex d enclosure.
Fig 4 shows how a 4/20mA output can be brought
via an Ex d gland from a flameproof enclosure and
displayed by a local BA304SG or BA324SG
indicator without the need for a Zener barrer or
galvanic isolator within the flameproof enclosure.
Fig 4 Monitoring equipment protected by a
flameproof enclosure in Zone 1 or 2.
A similar technique may be used to monitor
equipment protected by a pressurised Ex p
enclosure.
