BEKA BA337E, Руководство пользователя

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3.5 Pulse input terminals
The BA337E and BA338E Rate Totalisers have 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 BA337E or BA338E 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
3.5.1 Flowmeter sensors that don't 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 BA337E or BA338E 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.
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 BA337E or BA338E.
The BA337E and BA338E EC-Type Examination
Certificate specifies that the equivalent capacitance
and inductance of pulse 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 totaliser's pulse input terminals.
The totalisers pulse input equivalent capacitance
and inductance are small and unlikely to make a
significant
difference to the allowable cable
parameters.
3.5.2 Flowmeter sensors that require energising
Flowmeters with switch contacts, proximity detector
or open collector outputs require energising which is
achieved by linking Rate Totaliser terminals 3 and 4
together as described in section 3.5.
When
energised, the output parameters of the pulse input
terminals 5 and 6 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 the totaliser pulse input.
Any certified intrinsically safe flowmeter may be
connected to a BA337E or BA338E energised input
providing that:
a. The flowmeter is a certified intrinsically safe
device having input parameters equal to or
greater than:
Ui ≥ 10.5V dc
Ii ≥ 9.2mA dc
Pi ≥ 24mW
or
complies with the 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 BA337E or BA338E.
d. Minimum operating voltage of a flowmeter
incorporating a proximity detector is less than
7.5V.
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