BEKA BA337E, Manual

Page: 46 / 61

Using the
&
or
*
push button select
durAtion
in
the pulse output sub-menu and press
(
which will
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 in the sub-menu.
Note:
This function only appears in the pulse output
sub-menu when
5CALEd
is selected in the
5ource
sub-function (10.5.6).
10.5.9 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 Rate Totaliser is disconnected or turned
off, any stored pulses will not be retained.
10.6 4/20mA output
Both the BA337E and BA338E Rate Totalisers can be
supplied with a factory fitted galvanically isolated
4/20mA output which may be configured to represent
the rate or total display. Only one output option can
be fitted to a BA337E.
10.6.1 Intrinsic safety
The 4/20mA output has been certified as a separate
galvanically isolated intrinsically safe circuit complying
with the requirements for
simple apparatus.
This
allows terminals C1 and C3 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 maximum equivalent capacitance and inductance
of the 4/20mA output output is:
Ci = 2.2nF
Li = 4µH
To determine the maximum permissible cable
parameters, these figures should be subtracted from
the maximum cable capacitance and inductance
specified by the certificate for the Zener barrier or
galvanic isolator powering the 4/20mA output circuit.
10.6.2 System design
The Rate Totalisers 4/20mA output is a galvanically
isolated passive current sink i.e. not powered, but it
is totally isolated from all other Rate Totaliser
circuits. It is effectively a 2-wire 4/20mA transmitter
requiring a minimum supply of 10V with its current
being controlled by the Rate Totaliser. Subject to
complying with intrinsic safety interconnection
requirements, the terminals C1 and C3 may be
connected to another instrument, which will accept a
4/20mA transmitter input.
The 4/20mA current
output may also be transferred to the safe area via a
galvanic isolator or Zener barriers.
Terminals C2
and C4 are internally linked and may be used for
joining a return 4/20mA wire.
Fig 19 shows how a 2-channel Zener barrier may
be used to transfer the 4/20mA current output into
the safe area, alternatively a galvanic isolator may
be used.
Fig 19 Application of 4/20mA output
10.6.3 Configuration
When a Rate Totaliser is supplied with an optional
4/20mA output the configuration menu is extended
as shown in Fig 20. The 4/20mA output sub-menu
is accessed via the
4-20 oP
function.
The 4/20mA output sub-menu allows the 4/20mA
output to be controlled by the rate or the total display
and to be scaled.
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