BEKA BA317NE, Manual

Page: 36 / 40

9.5.6 Output pulse width:
durAtion
When
5CALEd
is selected in the
5ourCE
function as
described in section 9.5.4, the output pulse width in
milliseconds is defined by this function. One of 11
pulse widths may be selected:
0 . 1
0 . 5
1
2 . 5
5
10
25
50
100
250
500
Using the
&
or
*
push button select
durAtion
in
the pulse output sub-menu and press
(
to reveal the
existing pulse duration. The value can be changed by
pressing the
&
or
*
push button to select the
required value followed by the
)
button to return to
durAtion
prompt.
Note: This function only appears in the pulse output
sub-menu when
5CALEd
is selected in the
5ourCE
function.
9.5.7 Pulse storage
If the
diVidE
and
durAtion
functions are configured
such that the output pulse frequency with the specified
pulse width can not be output in real time, the number
of pulses will be stored and transmitted at the
maximum possible speed.
When the total display is reset to zero or the power
supply to the Tachometer is disconnected or turned
off, any stored pulses will not be retained.
9.6 4/20mA output
The BA317NE Tachometer can be supplied with a
factory fitted galvanically isolated 4/20mA output
which may be conditioned to represent any part of the
Tachometer speed display. Only one output option
can be fitted to a BA317NE.
9.6.1 Type nA certification
The optional 4/20mA output is a separate galvanically
isolated Ex nA circuit with the following input
parameters:
Ui = 30V dc
This allows the 4/20mA output to be connected to any
dc circuit providing that in normal operation the
maximum supply voltage is not greater than 30V dc..
Providing that the BA317NE Tachometer is correctly
installed in a panel enclosure located in Zone 2
complying with the requirements for Ex n protection,
the 4/20mA current output may be used to transmit
to suitably protected equipment located in Zone 1 or
2 of a hazardous area, or to equipment located in a
safe area.
Fig 19 Application of 4/20mA output
(Shown without recommended screened cables)
Fig 19 shows a typical application in which a
BA317NE Tachometer is mounted in an Ex n panel
enclosure located in Zone 2 is retransmitting the
4/20mA current to the safe area.
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 installing DIN rail mounted terminals incorporating
a fuse which can easily be opened as shown in Fig 2
to provide isolation. 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 cable
screens.
For some application Ex nA instrumentation
energised by a current limited power supply or
instrument that can be switched off, is often
considered adequate and to comply with the
requirements of the standard.
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