5
3.3
4/20mA input
The input safety parameters for the 4/20mA input,
terminals 1 and 3 are:
Ii
=
100mA
The indicators are current input instruments
incorporating an internal protection circuit that
defines the voltage developed between the input
terminals 1 and 3, therefore the ATEX certificate
does not specify a maximum input voltage Ui.
3.4
Certification label information
The certification information label is fitted on the
top surface of the instrument assembly. It shows
the ATEX and IECEx certification information and
BEKA associates name and location. Non
European certification information may also be
shown. The instrument serial number and date of
manufacturer are recorded on a separate label
inside the instrument enclosure.
BA304NG certification label
BA324NG certification label
4.
SYSTEM DESIGN FOR ZONE 2 GAS
HAZARDOUS AREAS.
4.1
Transmitter loops
Both models may be connected in series with
almost any Ex n protected 4/20mA current loop
and calibrated to display the measured variable or
control signal in engineering units. The indicators
are transparent to HART
®
signals.
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 EN
60079-14
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
indicator. This increases to 5.0V if the
indicator is fitted with an optional backlight
which is loop powered. See 9.4.1
Figs 2 illustrate a typical application in which an
indicator is connected in series with a 2-wire Ex n
transmitter.
Fig 2 Typical Zone 2 transmitter loop
To strictly comply with the requirements of
EN 60079:
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.
