BEKA BA384E, Manual

Page: 9 / 68

9
3.5 Pulse input terminals
The BA384G Rate Totaliser has two pulse inputs, A
and b, that may be individually configured for use
with different types of flowmeter. Each input is a
separate intrinsically safe circuit, although the
negative side of each input is internally connected to
the negative side of the power supply and the reset
terminal RS2. See Fig 1. The two inputs should
not be connected in parallel.
For flowmeters with sensors that require energising
to determine their state, such as a switch contact,
open collector or a 2-wire proximity detector in a
turbine flowmeter, fitting an external link between
terminals 3 & 4 of the BA384G for input A and
between terminals 7 & 8 for input b, connects an
internal 7V, 6mA supply to the respective input.
Energising is not required when a BA384G input is
connected to a voltage pulse source.
Fitting an energising link changes the output safety
parameters of each BA384G input as shown in the
following table which also shows the types of sensor
requiring energising (link fitting).
Output safety
parameters of each input.
Type of input Link* Uo Io Po
Switch contact Yes 10.5V 9.2mA 24mW
Proximity detector Yes 10.5V 9.2mA 24mW
Open collector Yes 10.5V 9.2mA 24mW
Magnetic pick-off No 1.1V 0.5µA 0.2mW
Voltage input (low) No 1.1V 0.5mA 0.2mW
Voltage input (high) No 1.1V 0.5mA 0.2mW
*For input A link terminals 3 and 4
*For input b link terminals 7 and 8
3.5.1 Flowmeters that don't require energising
Flowmeters employing magnetic pick-offs and
voltage pulse sensors do not require energising,
therefore terminals 3 & 4 for input A and terminals 7
& 8 for input b should not be linked. When not
energised i.e. without a link, each BA384G input
complies with the requirements for
simple
apparatus . For intrinsic safety purposes, sources of
energy with output parameters less than 1.5V;
100mA and 25mW are considered to be
simple
apparatus (Clause 5.7 of EN60079-11), which allows
their output parameters Uo, Io & Po to be ignored
when assessing the safety of an intrinsically safe
system, thus simplifying loop assessment and
documentation.
Almost any flowmeter with a voltage pulse output
may be directly connected to one of the BA384G
inputs in a hazardous area providing that:
a. The flowmeter is a certified intrinsically safe
device having output parameters equal to or
less than:
Uo ≤ 28V dc
Io ≤ 200mA dc
Po ≤ 0.84W
or complies with requirements for
simple apparatus.
b. The flowmeter and associated wiring can
withstand a 500V rms insulation test to earth.
c. The flowmeter is located in the same
hazardous area as the BA384G.
The BA384G EU-Type Examination Certificate
specifies that the equivalent capacitance and
inductance of each BA384G input is:
Ci = 2nF
Li = 4µH
To determine the maximum permissible cable
parameters these figures should be subtracted from
the maximum permitted output parameters Lo and
Co specified by the certificate for the flowmeter
connected to the BA384G input terminals. The
BA384G input parameters are small and therefore
unlikely to make a significant difference to the
allowable cable parameters.
3.5.2 Flowmeters that require energising
Flowmeters with switch contacts, proximity detector
or open collector outputs require energising which is
achieved by linking two BA384G terminals together
for each input as described in section 3.5. When
energised, the output parameters of each BA384G
Rate Totaliser input are:
Uo = 10.5V dc
Io = 9.2mA dc
Po = 24mW
These output parameters do not comply with the
requirements for
simple apparatus and should be
considered when assessing the safety of the
flowmeter connected to a BA384G input.