BEKA BA314E, Manual

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4.1.8 Remote reset
The Tachometer's run-time display may be remotely
reset to zero by connecting terminals RS1 and RS2
together for more than one second. Permanent
interconnection inhibits the run-time clock. Remote
resetting may be accomplished by any mechanically
operated switch located in the same hazardous area
as the Tachometer providing the switch and the
associated wiring can withstand a 500V rms insulation
test to earth. No Zener barrier is required.
A BA314G may also be remotely reset from the safe
area. Any switch may be used but a Zener barrier is
required to transfer the contact closure into the
hazardous area which may be combined with the
supply barrier so that only one package is required. A
diode return barrier is not suitable for this application.
Fig 2 illustrates how a BA314G may be reset from
both the safe and the hazardous area.
Note: The Tachometer may be configured to reset
the total display to zero by operating the
&
and
*
push buttons simultaneously for more
than two seconds in the totalising mode i.e.
when the instrument is displaying flow. See
section 6.15.
4.2 Use with Galvanic Isolators
Galvanic isolators are probably the simplest
intrinsically safe interface to install as they provide
isolation and do not require a high integrity earth
connection.
Any galvanic isolator may be used with the BA314G
providing it's certification is for use with apparatus in
the required Zone and gas group, and it's output
parameters do not exceed the input parameters of
the Tachometer terminals to which it is connected. It
must also have the correct function.
Fig 4 BA314G used with galvanic isolators.
Fig 4 illustrates the basic circuit that is used for all
BA314G Tachometer installations protected by
galvanic isolators. For simplicity, connections for
the pulse output, optional alarms and 4/20mA output
are shown in sections 6.20 and 9 of this manual.
The Tachometer’s pulse source may also be located
in the safe area as shown in Fig 5. An additional
galvanic isolator is used to transfer the signal to the
Tachometer in the hazardous area, although it may
be difficult to find isolators for transferring some
sensor outputs.
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