BEKA BA334E, Руководство пользователя, Страница: 7 / 64

7
CAUTION installation in Zone 0
When installed in a Zone 0 potentially explosive
atmosphere requiring EPL Ga apparatus, the
instrument shall be installed such that even in
the event of rare incidents, an ignition source
due to impact or friction between the aluminium
label and iron/steel is excluded.
No special conditions apply when the BA334G Rate
Totaliser is installed in Zone 1 or in Zone 2. This
allows the BA334G to be installed in all gas Zones
and to be used with most common industrial gases
except carbon disulphide and ethyl nitrite which
have an ignition temperature of 95°C.
3.3 Power supply
When installed in a hazardous area the BA334G
should be powered from a certified Zener barrier,
galvanic isolator or associated apparatus with an
intrinsically safe voltage output.
The safety parameters of terminals 1 and 2 are:
Ui = 28V dc
Ii = 200mA dc
Pi = 0.84W
Uo = 0
Io = 0
Any certified Zener barrier, galvanic isolator or
associated apparatus with output safety parameters
equal to or less than these input limits may be used.
The maximum equivalent capacitance and
inductance between terminals 1 and 2 is:
Ci = 2nF
Li = 4µH
To determine the maximum permissible cable
parameters the above figures, which are small and
may be ignored in some applications, should be
subtracted from the maximum permitted cable
parameters specified for the Zener barrier, galvanic
isolator or associated apparatus powering the
BA334G Rate Totaliser.
3.4 Pulse input terminals
The BA334G Rate Totaliser has a single pair of
pulse input terminals 5 and 6 that may be
configured for use with different types of flowmeter.
For flowmeters with transducers that require
energising to determine their state, such as switch
contacts or a 2-wire proximity detector in a turbine
flowmeter, an external link between terminals 3 & 4
of the BA334G connects an internal 7V, 6mA
supply to the input. Energising is not required
when the Rate Totaliser's input is connected to a
voltage pulse source.
Fitting an external link between terminals 3 & 4
changes the output safety parameters of the Rate
Totaliser input terminals 5 & 6 as shown in the
following table. This table also shows the types of
sensor requiring energising (link fitting).
Output safety parameters
Type of input Link 3 & 4 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 0.5mA
0.2mW
Voltage input (low)
No 1.1V 0.5mA
0.2mW
Voltage input (high)
No 1.1V 0.5mA
0.2mW
3.4.1 Flowmeter sensors not require energising
Flowmeters employing magnetic pick-offs or
voltage pulse sensors do not require energising,
therefore terminals 3 & 4 should not be linked.
When not energised i.e. without a link, the output
parameters of the pulse input terminals comply
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 the BA334G input 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.