20
When alarm 1 is programmed as a low alarm
and alarm 2 as a high alarm, the display
shown in Fig 11A will be produced providing
setpoint 1 is less than setpoint 2.
If the low
setpoint (1) is greater than the high setpoint
(2), or the function of the alarms is reversed,
the setpoints will be indicated by two single
segments on the right hand bargraph as
shown in Fig 11B.
If only one alarm is enabled the setpoint will be
indicated by a column extending from the
setpoint to the top of the display for a high
alarm, and from the setpoint to the bottom of
the display for a low alarm.
Fig 11A Set point display
Fig 11B Display with set points reversed
Annunciators above the digital display show
the status of both alarms, and the digital
display can be programmed to alternate
between the measured value and an alarm
identification.
Programmable functions
for
each alarm
include adjustable setpoint, hysteresis, alarm
delay and alarm accept.
When frequent
setpoint changes are required, a separate
menu provides direct access to both setpoints
from the display mode without giving the
operator access to the programme and alarm
menus.
A different security code may be
included to prevent tampering or accidental
adjustment.
9.2.1 Solid state output
Each alarm has a galvanically isolated single
pole solid state switch output as shown in
Fig 12. The outputs are polarised and current
will only flow in one direction. Terminal 8 and
10 should be connected to the positive side of
the supply.
Ron
=
5ohms + 0.6V
Roff
=
greater than 180k
Note: Because of the series protection diode
some test meters may not detect a closed
alarm output.
Fig 12 Equivalent circuit of each alarm output
9.2.2 Intrinsic safety
Each alarm output 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 5.7 of
EN60079-11. This allows each of the BA326C
alarm outputs to be connected to any
intrinsically safe circuit protected by a Zener
barrier or galvanic isolator providing that the
output parameters of each circuit do not
exceed:
Summary of Contents for ba326c
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