BEKA BA337E, Manual

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4.1.2 Pulse input
As shown in Figs 2 and 3 the BA337E and the
BA338E 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 input 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 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

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 and
the BA338E 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 and BA338E contain a configurable
debounce circuit to prevent false triggering. Three
levels of de-bounce protection are independently
available. 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 BA337E or BA338E
input, providing the input safety parameters of the
flowmeter (proximity detector) are equal to or greater
than the output safety parameters of Rate Totaliser's
pulse input. i.e.
Ui ≥ 10.5V dc
Ii ≥ 8.2mA 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
BA337E or BA338E and with the associated wiring
be able to withstand a 500V rms insulation test to
earth.
The Rate Totalisers contain a configurable debounce
circuit to prevent false triggering. Three levels of
debounce protection are independently available.
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 BA337E and BA338E input configuration
menu is a low level voltage pulse input intended for
use with an intrinsically safe magnetic pick-off.
When a Rate Totaliser is configured for
CoiL
and
terminals 3 & 4 are not linked, the input terminals 5
& 6 comply 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 Rate Totalisers
pulse input parameters Ci and Li which are small
and can often be ignored.
The flowmeter must be located within the same
hazardous area as the Rate Totaliser and with the
associated wiring be able to withstand a 500V rms
insulation test to earth.
The Rate Totalisers contain a configurable debounce
circuit to prevent false triggering of the instrument.
See section 6.7.
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