4. SYSTEM DESIGN FOR ZONE 2 GAS
HAZARDOUS AREAS
4.1 Transmitter loops
The BA354NE Rate Totaliser may be connected in
series with almost any Ex n
*
protected 4/20mA flow
loop and calibrated to display the rate of flow and
total flow in engineering units. There are four
design requirements:
1. The current flowing in the 4/20mA loop, must
not exceed 100mA in normal operation.
2. Wiring must comply with Clause 9 of
EN60079-14
Electrical installation in
hazardous areas
.
3. The instrument enclosure must be fitted with
Ex n or Ex e certified glands, conduit fittings or
blanking plugs.
4. The loop must be able to tolerate the additional
1.2V required to operate the Rate Totaliser.
This increases to 5.0V if the Rate Totaliser is
fitted with an optional backlight which is loop
powered. See 10.4.1
*
May also be connected into Ex e, Ex d or Ex p
4/20mA loops. see BEKA application note
AG310.
Figs 2 illustrate a typical application in which a
BA354NE Rate Totaliser is connected in series with
a 2-wire Ex n flow transmitter.
Fig 2 Typical Zone 2 transmitter loop
To strictly comply with the requirements of
EN60079:
14 Electrical installations design, selection
and erection
, each of the wires entering the
hazardous area should be individually fused and
contain a means of isolation. However, in practice
instrumentation energised by a current limited power
supply or instrument that can be switched off is often
considered adequate.
4.2 Remote indication
The BA354NE Rate Totaliser may be driven directly
from a safe area instrument with a 4/20mA output to
provide a remote display within a Zone 2 hazardous
area.
There are four design requirements:
1. The current flowing in the 4/20mA loop, must
not exceed 100mA in normal operation.
2.
Wiring must comply with Clause 9 of
EN60079-14
Electrical installation in
hazardous areas
.
3. The instrument enclosure must be fitted with
Ex n or Ex e certified glands, conduit fittings or
blanking plugs.
3. The 4/20mA output from the safe area
instrument must be able to supply the 1.2V
required to operate the Rate Totaliser. This
increases to 5.0V if the Rate Totaliser includes
an optional backlight which is loop powered.
See 10.4.1
Fig 3 shows a typical
application.
Fig 3 Remote indication in Zone 2 hazardous area
To strictly comply with the requirements of
EN60079:14
Electrical Installation in Hazardous
Areas
, each of the wires entering the hazardous
area should be individually fused and contain a
means of isolation. However, in practice
instrumentation energised by a current limited power
supply or instrument that can be switched off is often
considered adequate.
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