BEKA BA337E-SS, Manual

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When designing a system it is important to remember
that terminals 2, 6 and RS2 are interconnected within
the BA337E-SS See Fig 1.
Fig 3 BA337E-SS used with Zener barriers pulse
source in safe area.
4.1.1 Power supply
The BA337E-SS Rate Totaliser requires a minimum of
10V between terminal 1 & 2 and consumes:
10mA without optional backlight
plus 6mA when terminals 3 & 4 are linked
Any certified Zener barrier may be used to power a
BA337E-SS Rate Totaliser providing the output safety
parameters of the barrier are equal to or less than the
input safety parameters of terminals 1 & 2 of the Rate
Totaliser.
Although this allows a wide variety of barriers to be
used, a positive polarity 28V; 93mA; 300

Zener
barrier, which has an end-to-end resistance of about
340

, is an industry standard device which is
frequently used. With this barrier the supply voltage in
the safe area must be between 15.5V and the
maximum working voltage of the Zener barrier which,
depending upon manufacturer, will be approximately
26V.
Note: The optional factory fitted display backlight
increases the instrument's current
consumption and therefore increases the
minimum safe area operating voltage, see
section for details section 10.3 for details.
4.1.2 Pulse input
As shown in Figs 2 and 3 the BA337E-SS can
display the rate and total flow from flowmeters with a
wide variety of pulse outputs located in safe and
hazardous areas.
No Zener barrier is required in series with the pulse
input of the BA337E-SS if the intrinsically safe
flowmeter is located within the same hazardous area
as the Rate Totaliser.
The following table shows the Rate Totaliser's input
switching thresholds when conditioned for use with
flowmeters having different outputs, For reliable
totalisation the Rate Totaliser pulse input must fall
below the lower threshold and rise above the upper
threshold.
Input sensor
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

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.
4.1.3 Switch contact input
Any flowmeter with a mechanically or magnetically
activated switch contact located in the same
hazardous area as the Rate Totaliser may be directly
connected to pulse input terminals 5 and 6, 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 BA337E-SS
contain a configurable debounce circuit to prevent
contact bounce being counted. 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 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-SS 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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