User Guide

4.2 BA390XS
BA390XS lamps, unlike the BA390X, do not contain a
current regulator. The current drawn, and hence the
brightness, must be dened by an external resistor or an
external current regulator.
Caution
Connecting a BA390XS lamp to a non current
limited source may permanently damage the lamp.
BA390XS lamps are intended for use with low current
intrinsically safe logic outputs and their performance is
specied at 4mA. Fig 5 shows how one multiple output
bus-powered eldbus module can control up to six
BA390XS lamps.
BA390XS
Intrinsically
safe
digital
output
module
4mA
+
Fieldbus
Hazardous area
Fig 5 BA390XS lamp powered by multiple digital output
eldbus module
In this example the module has six isolated 12V outputs
each current limited at 4mA, so no additional current limit
is required.
When a BA390XS is powered from an intrinsically safe
voltage source such as a Zener barrier or galvanic isolator,
a series resistor is required to dene the lamp current.
Resistor value in k = IS supply voltage – 8
Required lamp current in mA
This current limiting resistor may be installed in the
hazardous area without additional certication using
the rules for Simple Apparatus dened in section 5.7 of
IEC 60079-11. The lamp current should be selected to
provide the required brightness – see section 2.2 of this
guide.
Fig 6 shows how four BA390XS lamps can be powered
from a 24V dc supply via a single industry standard 28V
300 Zener barrier or galvanic isolator. Each lamp
operates at a minimum current of 5mA when all the lamps
are illuminated, but the current rises and hence the lamp
brightness increases when the other lamps are switched
off.
BA390XS
+
Hazardous area Safe area
Barrier
28V 93mA barrier
or galvanic isolator
24V dc
5mA
1800

BA390XS
+
5mA
1800

BA390XS
+
5mA
1800

BA390XS
+
5mA
1800

Fig 6 Four BA390XS lamps powered from a common
barrier or isolator
5