BEKA BA337E, Manual

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Fig 5 Pulse source in safe area
4.2.1 Power supply
The BA337E and the BA338E Rate Totalisers require
a minimum of 10V between terminal 1 & 2 and
consume:
10mA without optional backlight
plus 6mA when terminals 3 & 4 are linked
Any galvanic isolator certified for the gas group and
Zone in which the BA337E or BA338E 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 the BA337E and BA338E
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 Rate Totaliser.
The BA337E and BA338E 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.
Input transducer
Switching thresholds
Lower Upper
Open collector
2k

10k

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

1000

Switch contacts, proximity detectors and open
collector sensors require energising which is
achieved by linking terminals 3 and 4 together as
shown in Figs 4 and 5.
4.2.3 Switch contact input
Any flowmeter with a magnetically activated switch
contact output may be directly connected to input
terminals 5 & 6 providing the flowmeter is located in
the same hazardous area as the Rate Totaliser and
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
BA337E and BA338E contain a configurable
debounce circuit to prevent contact bounce being
counted. Three levels of de-bounce protection are
independently available. 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 providing the flowmeter is located in
the same hazardous area as the Rate Totaliser, and
the flowmeter and associated wiring can withstand a
500V rms insulation test to earth.
The BA337E and BA338E contain a configurable
debounce circuit to prevent false triggering. Three
levels of de-bounce protection are independently
available. See section 6.7.
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