BEKA BA384E, Manual

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Fig 5 BA384G Rate Totaliser protected by
galvanic isolators with sensors in safe area.
4.2.1 Power supply
The BA384G requires a minimum of 10V between
terminal 1 & 2 and consumes:
10mA without optional backlight
plus 6mA when terminals 3 & 4 are linked
plus 6mA when terminals 7 & 8 are linked
plus 16mA with optional backlight
Any galvanic isolator certified for the gas group in
which the BA384G is installed may be used to power
the instrument. The output safety parameters of the
isolator must be equal to or less than the input
safety parameters of terminals 1 & 2 and the voltage
at terminals 1 & 2 must be greater than 10V. These
requirements are not restrictive and allow a wide
range of galvanic isolators, such as solenoid drivers,
to be used.
4.2.2 Pulse inputs
As shown in Figs 4 and 5 both BA384G inputs can
be directly connected to hazardous area flowmeters,
or to safe area flowmeters via isolators. Galvanic
isolators are not required in series with the input if
an intrinsically safe flowmeter is located within the
same hazardous area as the BA384G.
The BA384G Rate Totaliser may be used with
flowmeters having a wide variety of pulse outputs.
The following table shows the switching thresholds
for each type. For reliable operation the Rate
Totalisers input signal must fall below the lower
threshold and rise above the upper threshold.
Sensor
Switching thresholds
Lower Upper
Switch 100 Ω 1000 Ω
Proximity detector 1.2mA 2.1mA
Open collector 2k Ω 10k Ω
Magnetic pick-off 0mV 40mV peak
Voltage pulse low 1.0V 3.0V
Voltage pulse high 3.0V 10.0V
Switch contacts, proximity detectors and open
collector sensors require energising which is
achieved by linking two BA384G terminals together
for each input as shown in Figs 4 and 5.
4.2.3 Switch contact input
Any flowmeter with a mechanically or magnetically
activated switch contact output may be directly
connected to input terminals 5 & 6 or 9 &10. The
flowmeter should be located in the same hazardous
area as the BA384G, and the flowmeter and
associated wiring should be able to withstand a
500V rms insulation test to earth. Most
magnetically activated reed relays used in turbine
flowmeters comply with these requirements. The
BA384G contains a configurable debounce circuit to
prevent contact bounce being counted. Three levels
of de-bounce protection are independently available
for each input. See section 6.7.
4.2.4 Open collector input
Certified intrinsically safe flowmeters with an open
collector output may be directly connected to input
terminals 5 & 6 or 9 &10 providing the flowmeter is
located in the same hazardous area as the BA384G,
and the flowmeter and associated wiring can
withstand a 500V rms insulation test to earth.
The BA384G contains a configurable debounce
circuit to prevent false triggering. Three levels of de-
bounce protection are independently available for
each input. See section 6.7.