BEKA BA334NG, Руководство пользователя

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10. ACCESSORIES
10.1 Units of measurement & instrument
identification.
New BA334NG Rate Totalisers 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 fitted which
can easily be marked with a dry transfer or a
permanent marker on-site.
Custom printed scale cards are available as
accessories and may be easily fitted as shown in
section 5.4 of this manual.
The BA334NG can also be supplied with a blank or
custom laser engraved stainless steel legend plate -
see Fig 7. The plate, which after installation is
visible 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
10.2 Backlight
The BA334NG Rate Totaliser can be supplied with a
factory fitted backlight that produces green
illumination enhancing display contrast and enabling
it to be read at night or in poor lighting conditions.
The backlight is internally powered from the
instrument so that no additional wiring is required,
but the instrument supply current increases to
32mA.
10.3 Alarms
The BA334NG can be supplied with factory fitted
dual solid state single pole alarm outputs that may
be independently programmed as high or low, rate
or total alarms with normally open or normally
closed outputs.
Configurable functions for each alarm include
adjustable setpoint, alarm delay time and alarm
silence time. Hysteresis may be applied to rate
alarms.
CAUTION
Alarm outputs should not be used for
critical safety applications such as a shut
down system.
When the BA334NG power supply is turned off or
disconnected, 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 chosen for the
alarm condition.
Alarm annunciators on the instrument display
indicate the status of each alarm. If an alarm delay
or silence time has been selected the annunciator
will flash during the delay or silence period.
The BA334NG internal counters are up-dated and
compared with the alarm setpoint twice per
second, irrespective of the display update time
selected. This may result in an alarm being
delayed for up to half a second after the rate or
total has exceeded the setpoint.
10.3.1 Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output as shown in Fig 15. 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 = less than 5 Ω + 0.7V
Roff = greater than 1M Ω
Note: Because of the series protection diode
some test meters may not detect a closed
alarm output.
Fig 15 Equivalent circuit of each alarm output
10.3.2 Ex nA certification
Each alarm output is a separate galvanically
isolated Ex nA circuit with the following input
parameters:
Ui = 30V dc
Ii = 200mA
This allows each alarm output to switch any dc
circuit providing that in normal operation the
maximum supply voltage is not greater than 30V
dc and the switched current is not greater than
200mA.
Providing that the BA334NG Rate Totaliser is
correctly installed in Zone 2 the two alarm outputs
may be used to switch suitably protected
equipment located in Zone 1 or 2 of a hazardous
area, or equipment located in a safe area.