19
8.2.2
Separately powering the backlight
The optional backlight may also be powered from a
separate power supply as shown in Fig 13.
Fig 13 Backlight separately powered
When separately powered the backlight draws a
constant current providing the supply is equal to or
greater than the minimum specified voltage.
Below this supply voltage the backlight continues
to function but with reduced brilliance.
Current
Minimum voltage
Both models
34.7mA
11V
8.3
Alarms
Both models can be supplied with factory fitted
dual solid state, single pole, voltage free alarm
outputs. Each alarm output may be independently
configured as a high or low alarm with a normally
open or normally closed output in the non-alarm
condition.
When the 4/20mA current powering the indicator is
removed both alarm outputs will open irrespective
of configuration. The open circuit condition should
therefore be chosen as the alarm condition when
designing an alarm system.
Fig 14 illustrates the
conditions available and shows which are fail safe.
When an alarm occurs an alarm annunciator on
the indicator front panel is activated and if required
the numerical display can alternate between the
measured
value
and
the
alarm
channel
identification
ALr1
or
ALr2
.
CAUTION
Alarm outputs should not be used for critical
safety applications such as an emergency shut
down system.
The alarms are activated by the indicator’s
numerical display. Use of the Tare Function
tArE
will change the numerical display, the
alarms will continue to function at the original
displayed value, but this will correspond to a
different input current.
Fig 14 Alarm outputs
Configurable functions for each alarm include
adjustable setpoint, hysteresis, alarm delay and
alarm accept.
