17
Fig 8 Alarm outputs
Programmable functions for each alarm include
adjustable setpoint, hysteresis, alarm delay and
alarm accept.
9.2.1 Solid state output
Each alarm has a galvanically isolated single pole
solid state switch output as shown in Fig 9. The
outputs are polarised and current will only flow in
one direction. Terminals 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 9 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 5.4 of EN50020:1994.
This allows each of the BA324D 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:
Uo
28V dc
Io
200mA
Po
0.85W
No system certificate has been issued for the
BA324D alarm outputs, as the system certificate
for the circuit to which the alarms are connected
remains valid. Hazardous or safe area loads may
be switch as shown in Fig 10.
The maximum equivalent capacitance and
inductance of each BA324D alarm output is:
Ci
= 40nF
Li
= 20µH
To determine the maximum permissible cable
parameters, the equivalent alarm output
parameters must be subtracted from the maximum
cable capacitance and inductance specified by the
system certificate of the circuit connected to each
alarm.
Fig 10 Typical alarm application
