BEKA BA537E, Руководство пользователя

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3. SYSTEM DESIGN
Fig 2 illustrates the basic circuit that is used for all
BA537E and BA538E installations.
For simplicity,
connections for the pulse output and optional alarms
and 4/20mA output are shown separately in section
10 of this manual.
Fig 2 Basic BA537E and BA538E system
When designing a system it is important to remember
that terminals 2, 6 and RS2 are interconnected within
the BA537E and the BA538E See Fig 1.
3.1 Power supply
The BA537E and the BA538E Rate Totalisers require
a dc supply voltage between 10V and 30V at
terminals 1 & 2 and consume:
10mA without optional backlight
plus 6mA when terminals 3 & 4 are linked
As shown in Fig 1 terminals 2, 6 and RS2 of the
BA337E and BA338E Rate Totalisers are internally
connected together. Therefore these terminals should
only be connected to the same, or to an isolated
circuit.
3.2 Pulse input
As shown in Figs 2 the BA537E and the BA538E
can display the rate and total flow from flowmeters
with a wide variety of pulse outputs.
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 collector output require
energising which is achieved by linking Rate
Totaliser terminals 3 and 4 together.
3.2.1 Switch contact input
Any flowmeter with a mechanically or magnetically
activated switch contact may be directly connected
to the pulse input terminals 5 and 6. The BA537E
and the BA538E contain a configurable debounce
circuit to prevent contact bounce being counted.
See section 5.7.
3.2.2 Open collector input
Flowmeters with an open collector output may be
directly connected to input terminals 5 & 6. Polarity
of the sensor should be observerd. The BA537E
and BA538E contain a configurable debounce circuit
to prevent false triggering. Three levels of de-
bounce protection are independently available. See
section 5.7.
3.2.3 2-wire proximity detector input
Most flowmeters incorporating a NAMUR 2-wire
proximity detector may be directly connected to a
BA537E or BA538E input, providing the minimum
operating voltage of the flowmeter (proximity
detector) is less than 7.5V. The Rate Totalisers
contain a configurable debounce circuit to prevent
false triggering. Three levels of debounce protection
are independently available. See section 5.7.
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