BEKA BA317NE, Manual

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4.1 Power supply
The BA317NE Totaliser require a minimum of 10V
between terminal 1 & 2 and consumes:
10mA without optional backlight
plus 6mA when terminals 3 & 4 are linked
A 24V dc regulated supply with a current limit located
in a safe area is suitable. The power supply should
meet the requirements for personnel safety so that
‘live maintenance’ can safely be performed. The
implicit requirement for galvanic isolation from the
mains supply ensures that the possible difficulties
from circulating earth currents caused by mains faults
is minimised. In European terms if the power supply
is CE marked it is almost certainly acceptable.
To comply with the requirements of EN 60079: 14
Electrical installations design, selection and erection ,
each of the wires entering the hazardous area should
be individually fused and contain a means of isolation.
These two requirements may be satisfied by using
DIN rail mounted terminals incorporating an easily
removable fuse which can be extracted to achieve
isolation as shown in Fig 2. Clear identification of,
and easy access to the means of isolation is essential
for their effective use. It is also necessary to ensure
that the maintenance procedure makes sure that
unauthorised re-closure of the switches does not
occur. It is not considered necessary to have a means
of isolation or electrical protection for the screen.
Fig 2 DIN rail mounting terminals incorporating a fuse
For some applications Ex nA instrumentation
energised by a current limited power supply or
instrument that can be switched off, is considered
adequate and to comply with the requirements of the
standard.
4.2 Pulse input
The BA317NE can display speed and run-time from a
wide variety of pulse outputs speed sensors located in
a Zone 2 hazardous areas or in a safe area.
Fig 3 shows the connections when the sensor is
located in Zone 2 and Fig 4 the connections required
when the sensor is in a safe area.
Fig 3 Connections for sensor in Zone 2
Fig 4 Connections for sensor in safe area
Providing the BA317NE Tachometer is correctly
installed in an Ex n panel enclosure located in Zone
2, the input terminals may be connected to a
certified speed sensor located in Zone 1 as shown in
Fig 5. The speed sensor should have Ex e or Ex d
certification permitting installation in Zone 1.
Intrinsically safe Ex i certified flowmeter sensors
should not be used.
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