7
4.2 Non FISCO Systems
If the BA488CF-P PROFIBUS display is to be
connected to a fieldbus segment that does not
comply with FISCO requirements, the safety
parameters of the power supply and the
PROFIBUS Display must be compared using the
entity concept.
The maximum output safety parameters of the
device powering the fieldbus segment must be
equal to, or less than, the input safety parameters
of terminals 1 & 2 of the BA488CF-P PROFIBUS
display, namely:
Ui
=
17.5V dc
Ii
=
380mA dc
Pi
=
5.32W
The maximum permitted cable parameters for the
fieldbus segment must be reduced by the
equivalent internal capacitance Ci and inductance
Li of the BA488CF-P. The BA488CF-P equivalent
capacitance and inductance are very small and
make little practical difference.
Ci
= 1nF
Li
= 8µH
4.3 External switches
For applications requiring operator inputs to be
made by large industrial push buttons, terminals
S1 to S7 allow up to six external switches to be
connected to the BA488CF-P PROFIBUS Display.
When external switches are connected the front
panel push buttons may be operated in parallel or
disabled – see section 6.3.7
For installation in a hazardous area the switches
and associated wiring must comply with the
requirements for
simple apparatus
. i.e. the switch
must be mechanically activated and have IP20
protection, and both the switch and the wiring must
be capable of withstanding a 500V rms insulation
test to earth for one minute. Most industrial push
buttons and wiring satisfy these requirements.
Although the allowable cable parameters are large,
it is recommended that the cables are less than 5m
long.
If a safe area switch is to be connected to a
Fieldbus Display located in a hazardous area, the
switch contact must be transferred via a certified
intrinsically safe relay or a galvanic isolator having
zero output safety parameters as shown in Fig 3.
Fig 3
External
push button
switch in safe area
4.4 Alarm outputs
Each alarm output is a galvanically isolated single
pole solid state switch output as shown in Fig 4.
Fig 4 Equivalent circuit of each switch output
The outputs are polarised and current will only flow
in one direction. Odd numbered terminals should
be connected to the positive side of the supply.
Ron
=
5
+ 0.7V
Roff
=
greater than 1M
Note:
Because of the series protection diode,
some test meters may not detect a closed alarm
output
WARNING
These Alarm Outputs should not be used
for critical safety applications such as an
emergency shut down system.
When the BA488CF-P PROFIBUS display is
disconnected from the fieldbus, or the fieldbus is
de-energised all the alarm outputs will open
irrespective of how they have been configured.