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5.4 USE WITH GALVANIC ISOLATORS
Galvanic isolators are probably the easiest
intrinsically safe interface to use as they provide
isolation and do not require a high integrity earth
connection.
Any EEx ia IIC certified intrinsically safe galvanic
isolators may be used with the BA364D providing
the output parameters do not exceed the input
parameters of the terminals to which they are
connected.
To assist with system design, the galvanic
isolator system certificate lists some of the
isolators that may be used and defines the
maximum permitted cable parameters.
Fig 5.2 illustrates the basic circuit that is used for
all BA364D clock installations protected by
galvanic isolators.
Fig 5.2 Basic clock circuit using isolators
5.4.1 Power supply
The BA364D galvanic isolator system certificate
lists a wide range of certified galvanic isolators
that may be used to power the instrument. If
using the entity concept to select an isolator, in
addition to matching the safety parameters, the
isolator must be capable of supplying 10V dc
minimum at 15mA to the BA364D.
5.4.2 Synchronisation
When terminals 7 & 8 are connected together
the displayed time will be automatically set to the
preprogrammed reset time. The clock will be
inhibited until terminals 7 & 8 are disconnected
from each other, when it will restart from the
preprogrammed time. To achieve reliable
synchronisation terminals 7 & 8 should be
connected together by a pair of contacts which
close for at least one second. This function
enables one or more BA364D clocks to be
synchronised with a master clock once every 24
hours.
Synchronisation may be accomplished by any
mechanically operated switch located in the
hazardous area providing it can withstand a 500V
rms insulation test to earth for one minute. No
galvanic isolator is required.
The BA364D may also be synchronised from
within the safe area. Any switch may be used,
but a galvanic isolator or intrinsically safe relay is
required to transfer the contact closure into the
hazardous area. See system certificate for a list
of some devices that may be used. Fig 5.2
illustrates how the BA364D may be synchronised
from both the safe and the hazardous area.
5.4.3
Optional control outputs
The BA364D can be supplied with two isolated
solid state control outputs. Each output may be
programmed to turn on and off twice during a
twenty four hour period. These outputs may be
used to switch certified intrinsically safe devices
within the hazardous area, or the contacts may
be transferred to the safe area via a galvanic
isolator.
