BEKA BA384E, Manual

Page: 12 / 68

12
13.5V min without optional backlight
18.9V min with optional backlight
plus 2.1V when terminals 3 & 4 are linked
plus 2.1V when terminals 7 & 8 are linked
4.1.2 Pulse inputs
As shown in Fig 2 both BA384G Rate Totaliser
inputs may be connected to hazardous area
flowmeters with a wide variety of outputs, or to safe
area flowmeters as shown in Fig 3.
No Zener barrier is required in series with each input
if the intrinsically safe flowmeter is located within the
same hazardous area as the BA384G. The
following table shows the Rate Totaliser's input
switching thresholds when configured to operate
with various sensors. For reliable operation input
pulses must fall below the lower threshold and rise
above the upper threshold.
Flowmeter output
Switching thresholds
Lower Upper
Switch contacts 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
Flowmeters with a switch contact, proximity detector
or an open collector output require energising which
is achieved by linking two BA384G terminals
together for each input as shown in Figs 2 & 3.
4.1.3 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 debounce protection are independently available
for each input. See section 6.7.
4.1.4 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.
4.1.5 2-wire proximity detector input
Most certified intrinsically safe flowmeters
incorporating a NAMUR 2-wire proximity detector
may be directly connected to a BA384G input,
providing the input safety parameters of the
flowmeter (proximity detector) are equal to or greater
than the output safety parameters of a BA384G
input. i.e.
Ui ≥ 10.5V dc
Ii ≥ 9.2mA dc
Pi ≥ 24mW
and the minimum operating voltage of the flowmeter
(proximity detector) is less than 7.5V. The flowmeter
must be located in the same hazardous area as the
BA384G and with the associated wiring be able to
withstand a 500V rms insulation test to earth.
The BA384G contains a configurable de-bounce
circuit to prevent false triggering. Three levels of
debounce protection are independently available for
each input. See section 6.7.
4.1.6 Magnetic pick-off input
Flowmeters incorporating a magnetic pick-off to
sense flow will have a low level voltage output
unless the flowmeter incorporates an amplifier.
CoiL
in the BA384G input configuration menu is a low
level voltage pulse input intended for use with an
intrinsically safe magnetic pick-off. When a BA384G
input is configured for
CoiL
it complies with the
requirements for simple apparatus allowing
connection to any certified intrinsically safe magnetic
sensor having output parameters equal to or less
than:
Uo ≤ 28V dc
Io ≤ 200mA dc
Po ≤ 0.84W
The maximum permitted cable parameters will be
the magnetic pick-off's Co and Lo specified on it's
intrinsic safety certificate, less the BA384G input
parameters Ci and Li which are small and can often
be ignored.