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8.4 Display backlight
The BA504E and BA524E 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 to 5V.
When separately powered the backlight is brighter,
but additional field wiring and a power supply are
required.
Fig 15 Terminals for optional backlight
8.4.1 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 16, which increases the maximum indicator
voltage drop from 1.2 to 5V.
Fig 16 Loop powered backlight
Providing the increased voltage drop can be
tolerated the intrinsic safety and system design
described in sections 3 and 4 of this manual
remain valid with the backlight loop powered.
8.4.2 Separately powering the backlight
The optional backlight may also be powered from a
separate power supply as shown in Fig 16.
Fig 17 Separately powered backlight
The separately powered backlight is a current sink
which will draw a constant 34.7mA when the
voltage between terminal 12 and 14 is greater than
11V. If the supply voltage is less than 11V the
backlight will continue to function but the brilliance
will be reduced.
Current Minimum voltage
BA504E & BA524E
34.7mA
11V
