BEKA BA368C, Руководство пользователя

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2.3.2 Input
When the BA368C is programmed as a counter
both input A and input B are operational and may
be independently programmed to operate with
almost any pulse output transducer.
The following table shows the switching thresholds
for the various transducers, plus the maximum
operating frequency. For reliable counting the
input signal must fall below the lower threshold and
rise above the upper threshold.
Input Switching
thresholds
Freq.
max
Switch 100
Ω
1000
Ω
100Hz
Proximity
detector
1.2mA 2.1mA 5kHz
Open
collector
2k
Ω
10k
Ω
5kHz
Magnetic
pick-off
0mV 20mV
peak
5kHz
Voltage
pulse
1.0V 3.0V 5kHz
The intrinsic safety requirements are explained in
section 1.4.3 Almost any mechanically or
magnetically activated switch, intrinsically safe
NAMUR 2-wire proximity detector or intrinsically
safe voltage may be directly connected to the input
terminals.
If the BA368C is located in a hazardous area but
the transducer(s) is in a safe area, a Zener barrier
is required to transfer the transducer output to the
instrument. The system certificate defines barriers
which may be used.
2.3.3 Resetting the total display
When terminals 7 & 8 are connected together the
total display will be reset. To achieve reliable
resetting the contacts must close for at least one
second.
Resetting may be accomplished by any
mechanically operated switch located in the
hazardous area providing it can withstand a 500V
rms insulation test to earth for one minute. No
Zener barrier is required.
The BA368C may also be reset from within the
safe area. Any switch may be used but a Zener
barrier is required to transfer the contact closure
into the hazardous area. A diode return barrier
may be combined with the supply barrier so that
only one dual channel device is required. The
system certificate lists some of devices that may
be used.
Fig 2.1 illustrates how the BA368C counter total
display may be reset from both the safe and the
hazardous area.
2.3.4 Options
When the BA368C is calibrated as a counter,
optional alarms, a 4/20mA analogue output and a
re-transmitted pulse output may be used. The
intrinsic safety features of these options are
described in section 1 of this manual and the
counter applications in sections 2.6, 2.7 and 2.8.
2.4 USE WITH GALVANIC ISOLATORS
Galvanic isolators are probably the easiest
intrinsically safe interface to use as they provide
isolation and do not require a high integrity earth
connection.
Any EEx ia IIC certified intrinsically safe galvanic
isolators may be used with the BA368C providing
the output parameters do not exceed the input
parameters of the terminals to which they are
connected.
To assist with system design, the galvanic isolator
system certificate lists some of the isolators that
may be used and defines the maximum permitted
cable parameters.
Fig 2.2 illustrates the basic circuit that is used for
all BA368C counter installations protected by
galvanic isolators. Intrinsic safety requirements
are explained in section one of this manual which
should be read before the system is designed.
If the total display is reset from the instrument front
panel, or from an external switch in the hazardous
area, only the power supply galvanic isolator is
required.
Fig 2.2 Basic counter circuit using isolators