19
9.
ACCESSORIES
9.1
Units measurement & instrument
identification.
New BA304NG and BA324NG indicators are
supplied with a printed scale card showing the
units of measurement and tag information specified
when the instrument was ordered. If this
information was not supplied a blank scale card will
be supplied which can easily be marked with a dry
transfer or a permanent marker.
Custom printed scale cards are available as
accessories and may be easily fitted as shown in
section 5.4 of this manual.
Both indicators can also be supplied with a blank
or custom laser engraved stainless steel legend
plate - see Fig 5. The plate, which after installation
is visable from the front of the instrument, is
supplied loose with two fixing screws for securing it
to the rear of the instrument's back-box. This plate
can typically accommodate:
1 row of 5 alphanumeric characters 10mm high
or 1 row of 6 alphanumeric characters 7mm high
or 2 rows of 10 alphanumeric characters 5mm high
9.2
Display backlight
The BA304NG and BA324NG loop powered
indicators can be supplied with a factory fitted
backlight that may be loop or separately powered.
When loop powered the backlight produces green
background illumination enabling the display to be
read at night or in poor lighting conditions. No
additional power supply or field wiring are required,
but the indicator voltage drop is increased. When
separately powered the backlight is brighter, but an
additional field wiring is required.
Fig 10 Terminals for optional backlight
9.2.1
Loop powering the backlight
The backlight is loop powered by connecting it in
series with the indicator’s 4/20mA input as shown
in Fig 11, which increases the maximum indicator
voltage drop from 1.2 to 5V.
Fig 11 Backlight loop powered
To strictly comply with the requirements of
EN 60079:14
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.
