9
4.3
Use with Galvanic Isolators
Galvanic isolators are probably the simplest
intrinsically safe interface as they provide isolation
and do not require a high integrity earth
connection.
Any certified galvanic isolator with output
parameters less than the input parameters of the
BA338C may be used. The BA338C system
certificates list some of the suitable devices
together with the maximum permitted cable
parameters
Fig 4 BA338C used with galvanic isolators
Fig 4 illustrates the basic circuit that is used for all
BA338C installations protected by galvanic
isolators. For simplicity, connections for the
optional pulse output, 4/20mA output and backlight
are included in the appendix to this manual.
Alternatively the pulse source may be located in
the safe area. Fig 5 shows how an additional
galvanic isolator is used to transfer the signal to
the rate totaliser in the hazardous area.
Fig 5 Pulse source in safe area
4.3.1 Power supply
Any certified galvanic isolator may be used to
power the BA338C providing the output safety
parameters are less than the maximum input
parameters of terminals 1 & 2. In addition to
matching the safety parameters, the isolator must
be capable of supplying at least 25mA at 10Vdc to
the BA338C. The BA338C system certificates list
some of the suitable devices together with the
maximum permitted cable parameters.
4.3.2 Pulse input
As shown in Fig 4 the BA338C will count pulses
from a wide variety of sources. Terminals 5 and 6
are for sources that need powering e.g. a switch
contact or a 2-wire NAMUR proximity detector.
Terminals 3 and 4 are for voltage inputs. Only one
input may be used at a time, i.e pulses can not be
counted at terminals 3 & 4 and at 5 & 6 at the
same time. No galvanic isolator is required in
series with the input if the pulse source is located
within the hazardous area.
