BEKA BA314E, Manual

Page: 26 / 58

6.20 Pulse output
All BA314G Tachometers have an isolated open
collector pulse output having the following
parameters:
Ron = 60

+ 3V
Roff = 1M
Imax = 10mA
The output pulse may be a synchronous duplicate of
the input pulse or may be scaled and the pulse length
extended.
6.20.1 Intrinsic safety
The pulse output is an optically isolated separate
intrinsically safe circuit that has zero output safety
parameters. The output therefore complies with the
requirements
for simple apparatus . This allows pulse
output terminals P1 and P2 to be connected to any
intrinsically safe circuit protected by a certified Zener
barrier or galvanic isolator providing the output
parameters do not exceed:
Uo = 28V dc
Io = 200mA
Po = 0.84W
The equivalent capacitance and inductance of the
pulse output are both zero which allows the maximum
permissible cable parameters specified by the
certificate for the Zener barrier or galvanic isolator
powering the pulse output circuit to be used.
6.20.2 System design
The Tachometer pulse output is a passive circuit i.e.
not powered, but it is totally isolated from all other
Tachometer circuits. Subject to complying with
intrinsic safety interconnection requirements, the
terminals P1 and P2 may be connected to another
instrument which will accept an open collector input.
The pulse output may also be transferred to the safe
area via a galvanic isolator or a Zener barrier.
Fig 11 shows how a 2-channel Zener barrier may be
used to produce a voltage pulse in the safe area that
could be used to drive a safe area tachometer. The
positive terminal of the pulse output circuit P1 is
connected to the BA314G Tachometer’s positive
supply terminal 1 at the instrument. When an output
pulse occurs and the open collector 'closes', P2 is
connected to P1 and a pulse output current flows
through the diode return barrier to resistor R1 in the
safe area. The current flowing in the circuit is
determined by resistor R1 which should be chosen to
limit the output current to less than 10mA. For a 24V
supply R1 should therefore be greater than 2,200
Ω
Fig 11 Transferring pulse output to safe area using
Zener barriers
6.20.3 Configuration
The pulse output configuration sub-menu
PuL5E . oP
is shown in Fig 12.
.
The pulse output sub-menu allows the source of the
output pulse to be selected in the
5ourCE
sub-
function. For re-transmission applications the
output pulse may be a synchronous duplicate of the
input pulse by selecting
dirECt
in the
5ourCE
sub-
function.
When
5CALEd
is selected, two additional functions,
diVidE
and
durAtion
are introduced into the sub-
menu enabling the input pulse frequency to be
divided to produce the output pulse frequency, and
the output pulse width (duration) to be lengthened.
6.20.4 Access Pulse output sub-menu:
PuL5E . oP
Access the Tachometer configuration menu as
described in section 6.2. Using the
&
and
*
push
buttons scroll though the menu until
PuL5E . oP
is
displayed, pressing
(
will then access the pulse
output sub-menu which is shown in Fig 12.
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