BEKA BA334E, Руководство пользователя, Страница: 13 / 64

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Fig 5 Pulse source in safe area
4.2.1 Power supply
The BA334G 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.
Total increases to 32mA when optional backlight is
fitted. Any galvanic isolator certified for the gas
group and Zone in which the BA334G 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 input
As shown in Figs 4 and 5 the BA334G 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 BA334G 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 Ω 10k Ω
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 Ω 1000 Ω
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 mechanical or 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 BA334G
contains 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
Most certified intrinsically safe flowmeters with an
open collector output may be directly connected to
a BA334G input terminals 5 & 6, providing the
input safety parameters of the flowmeter (open
collector) 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
The flowmeter must be located in the same
hazardous area as the BA334G and the
associated wiring should be able to withstand a
500V rms insulation test to earth.
The BA334G contains a configurable debounce
circuit to prevent false triggering. Three levels of
de-bounce protection are independently available.
See section 6.7.