BEKA BA334NG, Manual

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4.2 Pulse input
The BA334NG can display the rate and total flow
from flowmeters with a wide variety of pulse outputs
located in a Zone 2 hazardous areas or in a safe
area. Fig 3 shows the connections when the
flowmeter is located in Zone 2 and Fig 4 the
connections required when the flowmeter is in a
safe area.
Fig 3 Connections for flowmeter sensor in Zone 2
Fig 4 Connections for flowmeter sensor in safe area
Providing the BA334NG Rate Totaliser is correctly
installed in Zone 2, the input terminals may be
connected to a certified flowmeter sensor located in
Zone 1 as shown in Fig 5. The flowmeter sensor
should have Ex e or Ex d certification permitting
installation in Zone 1. Intrinsically safe Ex i
certified flowmeter sensors should not be used.
Fig 5 Connection to an Ex d or Ex e flowmeter in
Zone 1.
4.2.1 Input switching thresholds
For reliable totalisation the Rate Totaliser pulse
input must fall below the lower threshold and rise
above the upper thresholds shown in the following
table.
Input transducer
Switching thresholds
Lower Upper
Open collector 2k Ω 10k Ω
Voltage pulse low 1.0V 3.0V
Voltage pulse high 3.0V 10.0V
Magnetic pick-off 0mV 40mV peak
Proximity detector 1.2mA 2.1mA
Switch 100 Ω 1000 Ω
Flowmeters with a switch contact, proximity
detector or an open collector output require
energising which is achieved by linking Rate
Totaliser terminals 3 and 4.
4.2.2 Switch contact input
Any flowmeter with a mechanically or magnetically
activated switch contact located in Zone 2 or in the
safe area may be directly connected to pulse input
terminals 5 and 6 which are non incendive,
providing the flowmeter and associated wiring can
withstand a 500V rms insulation test to earth.
Most magnetically activated reed relays used in
turbine flowmeters comply with these
requirements. The BA334NG contains a
configurable debounce circuit to prevent contact
bounce being counted. See section 6.7.