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9. ACCESSORIES
9.1 Scale card
The BA338C has a window on the right hand side
of the display to hold a card showing the units of
measurement e.g. Litres, Gallons, M
3
.
Instruments can be supplied with a printed scale
card showing any units specified at the time of
ordering. If a printed card is not requested, a blank
card will be supplied.
Scale cards can easily be marked on-site as
follows:
a. Remove the rear terminal block(s) and the
rear panel as shown in Fig 10.
b. Carefully pull the rate totaliser assembly
from the enclosure.
c. Gently pull and then slide the blank scale
card towards the display window until the
card is free. Mark the card with the required
legend and replace in the slot.
d. Reassemble the instrument.
9.2 Tag number
The BA338C can be supplied with a thermally
printed tag number on the rear panel. This tag
number is not visible from the front of the
instrument after installation.
9.3 Alarms
The BA338C can be supplied with two solid state
single pole outputs which may be independently
programmed as high or low, rate or total alarms
with normally open or normally closed outputs.
WARNING
These alarm outputs should not be used
for critical safety applications such as a
shut down system.
When the BA338C power supply is turned off or
disconnected, both BA338C alarm outputs will
open irrespective of whether normally open or
normally closed outputs have been selected.
When designing a system an open output should
therefore be the alarm condition.
Alarm annunciators on the instrument display
indicate the status of both alarms. If an alarm delay
or silence time has been selected the annunciator
will flash during the delay or silence period.
Programmable functions for each alarm include
adjustable setpoint, alarm delay time and alarm
silence time. Hysteresis may be applied to rate
alarms.
The BA338C total display is up-dated and
compared with the programmed alarm setpoint
twice per second, irrespective of the display
update time selected. This may result in the total
alarm being delayed for up to half a second after
the total has exceeded the setpoint.
9.3.1 Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output as shown in Fig 11. The
outputs are polarised and current will only flow in
one direction. Terminals A1 and A3 should be
connected to the positive side of the supply.
Ron
=
5
Ω
+ 0.6V
Roff
=
greater than 180k
Note:
Because of the series protection diode
some test meters may not detect a closed
alarm output
Fig 11 Equivalent circuit of each alarm output
9.3.2 Intrinsic safety
Each of the two alarm outputs is a separate
galvanically isolated solid state switch. The EC-
Type Examination Certificate specifies that under
fault conditions the voltage, current and power at
each alarm output will not exceed those specified
for
simple apparatus in Clause 5.4 of
EN50020:1994. This allows each of the BA338C
alarm outputs to be connected to any intrinsically
safe circuit protected by a certified Zener barrier or
galvanic isolator providing that the output
parameters of each circuit do not exceed:
Uo
28V dc
Io
200mA
Po
0.85W
No system certificate has been issued for the
BA338C alarm outputs, as the system certificate
for the circuit to which the alarms are connected
remains valid.
