BEKA BA334E, Руководство пользователя, Страница: 12 / 64

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4.1.8 Remote reset
The Rate Totaliser's total display may be remotely
reset to zero by connecting terminals RS1 and RS2
together for more than one second. Permanent
interconnection inhibits totalisation. Remote
resetting may be accomplished by any mechanically
operated switch located in the same hazardous area
as the Rate Totaliser providing the switch and the
associated wiring can withstand a 500V rms
insulation test to earth. No Zener barrier is required.
A BA334G 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 BA334G may be
reset from both the safe and the hazardous area.
Note: The Rate Totaliser may be configured to
reset the total display to zero by operating
the
&
and
*
push buttons simultaneously
for more than three seconds in the totalising
mode i.e. when the instrument is displaying
flow. See 6.19
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
BA334G 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 Rate Totaliser terminals to which
it is connected. It must also have the correct
function.
Fig 4 BA334G used with galvanic isolators.
Fig 4 illustrates the basic circuit that is used for all
BA334G installations protected by galvanic
isolators. For simplicity, connections for the pulse
output, optional alarms and 4/20mA output are
shown separately in sections 6.24 and 10 of this
manual.
The totaliser pulse source may be located in the
safe area as shown in Fig 5. An additional
galvanic isolator is used to transfer the signal to
the rate totaliser in the hazardous area, although it
may be difficult to find isolators for transferring
some flowmeter transducer outputs.