BEKA BA337E, Manual

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10.5 Pulse output
All BA338E Rate Totalisers are supplied with an opto-
isolated pulse output. The pulse output is available as
a factory fitted option on the smaller BA337E Rate
Totaliser, but only one output option can be fitted to
this model.
The pulse output is an open collector having the
following parameters:
Ron = 60

+ 3V
Roff = 1M
I max = 10mA
The output pulse may be a duplicate of the input pulse
for re-transmission applications, or it may be derived
from the least significant digit of the total display.
When derived from the total display the output pulse
frequency may be divided and the output pulse width
defined.
The retransmitted RTx annunciator on the instrument
display shows the status of the retransmitted pulse
output. Annunciator activation depends upon the
setting of
5ource
in the pulse output configuration
menu.
5caled:
Annunciator activated each time pulse output
open collector is
on
, i.e. Ron is less than 60 Ω
+ 3V.
direct:
Annunciator continuously activated
10.5.1 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 dc
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.
10.5.2 System design
The Rate Totalisers pulse output is a passive circuit
i.e. not powered, but it is totally isolated from all other
Rate Totaliser circuits.
Subject to complying with
intrinsic safety interconnection requirements, the
terminals P1 and P2 may be connected to another
instrument with an open collector input. The pulse
output may also be transferred to the safe area via a
galvanic isolator or a Zener barrier.
Fig 17 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 counter.
The
positive terminal of the pulse output circuit P1 is
connected to the Rate totaliser’s positive supply
terminal 1. When an output pulse occurs and the
open collector output ‘closes’, P2 is connected to P1
and the pulse current flows through the diode return
barrier to resistor R1 in the safe area. The current
flowing in the circuit is determined by R1 which
should be chosen to limit the pulse output current to
less than 10mA. For a 24V supply R1 should be
greater than 2,200
Ω .
Fig 17 Transferring pulse output to the safe area
using Zener barriers
10.5.3 Configuration
All BA338E Rate Totalisers are supplied with an
opto-isolated pulse output, the pulse output is also
available as a factory fitted option on the smaller
BA337E.
Therefore the pulse output menu shown
in Fig 18 appears in the configuration menu of all
BA338E Rate Totalisers, but only in the configuration
menu of BA337E Rate Totalisers having an optional
factory fitted pulse output.
The pulse output sub-menu enables the source of
the output pulse to be selected in the
5ourCE
sub-
function. For re-transmission applications the
output pulse may be a duplicate of the input pulse by
selecting
dirECt
in the
5ourCE
sub-function.
Alternatively, selecting
5CALEd
derives the output
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