25
Fig 10 Equivalent circuit of each alarm output
Note:
Because of the series protection diode
some test meters may not detect a
closed alarm contact.
9.2.2 Type n certification
Each of the two alarm outputs is a galvanically
isolated solid state switch which has been certified
as a separate Ex nL Group II, Category 3G circuit.
The input safety parameters for each alarm are:
Ui
30V dc
Ii
100mA
This allows each alarm output to switch any dc
circuit providing that in normal operation the
maximum supply voltage is not greater than 30V,
and the maximum current is not greater than
100mA.
Fig 11 shows a typical application in which alarm
one has been programmed as a flow alarm to
control a solenoid valve. Alarm two has been
programmed as a total alarm which turns a pump
off when the total flow exceeds the setpoint.
Fig 11 Typical alarm application
9.2.3 Programming and adjustment
When a BA354ND is supplied with alarms the main
programme menu is extended as shown in Fig 12.
The two alarm functions appear between the 'C--P'
and the 'SCALE-t' functions, and each alarm may
be programmed as a rate or a total alarm.
For simplicity Fig 12 only shows the programmable
functions on the rate option of alarm AL1. Alarm 2
and the total options are identical except that the
total alarms do not have hysteresis.
The following table summarises each of the alarm
programme functions and includes a cross
reference to more detailed information. Again
only the functions on alarm AL1 are listed.
Summary of programmable alarm functions
Display Description of function
'EnbL'
Alarm enable
Enables or disables the alarm function
without changing the alarm parameters.
See section 9.2.4
'tYPE'
Type of alarm
Defines whether the alarm operates on
the rate or total display.
See section 9.2.5
'SPr1'
Alarm setpoint 1
or
Adjusts the alarm setpoint. The
'SPt1'
alarm is activated when the rate or total
display equals the setpoint.
See section 9.2.6
'HI.LO'
Alarm function
Defines whether the alarm has a high
or low function
See section 9.2.7
'no.nc'
Normally open or normally closed
output
Determines whether the single pole
alarm output is open or closed in the
non alarm condition.
See section 9.2.8
'HStr'
Hysteresis
Adjusts the alarm hysteresis. Only
available on rate alarms.
See section 9.2.9
