BEKA BA334D, Manual

Page: 8 / 43

8
The following table shows the switching
thresholds for the various transducers, plus the
maximum operating frequency and the input
terminal numbers. For reliable counting the
input signal must fall below the lower threshold
and rise above the upper threshold.
Switching
thresholds
Freq
max
Input
terminals
Switch
100
Ω
1000
Ω
100Hz 5 & 6
Proximity
detector
1.2mA 2.1mA 5 kHz 5 & 6
Open
collector
2k
Ω
10k
Ω
5kHz 5 & 6
Magnetic
pick-off
0mV 20mV
peak
5kHz 3 & 4
Voltage
pulse
1.0V 3.0V 5kHz 3 & 4
4.2.3 Switch contact input
Any mechanically activated switch contact
located in the hazardous area may be directly
connected to terminals 5 & 6 providing it can
withstand a 500V rms insulation test to earth.
This includes most magnetically activated reed
relays used in turbine flowmeters. The
BA334D contains filtering to prevent contact
bounce being counted, this limits the maximum
operating frequency for a switch contact to
100Hz.
4.2.4 2-wire proximity detector input
Any certified intrinsically safe 2-wire proximity
detector complying with NAMUR switching
thresholds may be used, providing the input
safety parameters are greater than the output
safety parameters of terminals 5 & 6. The
system certificates list some of the acceptable
devices.
When programmed to operate with a proximity
detector, the BA334D maximum input
frequency is 5kHz.
4.2.5 Voltage pulse input
Voltage pulse sources should be connected to
terminals 3 and 4. These terminals comply
with the requirements for simple apparatus and
may be directly connected to any certified
intrinsically safe voltage source within the
hazardous area which can withstand a 500V
rms insulation test to earth for one minute and
has output parameters equal to or less than:
Uo = 28V dc
Io = 100mA dc
Po = 0.7W
This enables the BA334D to be connected
directly to most flowmeters incorporating a
certified intrinsically safe magnetic pick-off, or
a certified intrinsically safe amplifier producing
a high level pulse output. The BA334D has
two programme selectable voltage switching
thresholds, ‘COIL’ for magnetic pick-offs and
‘UOLtS’ for higher voltage pulses.
Maximum voltage pulse counting frequency is
5kHz.
Fig 3 Pulse source in safe area
4.2.6 Remote reset
The BA334D total display is reset to zero
when terminals 7 & 8 are connected together
for more than one second.. Permanent
interconnection inhibits totalisation. Remote
resetting may be accomplished by any
mechanically operated switch located in the
hazardous area providing it can withstand a
500V ac insulation test to earth. No Zener
barrier is required.
The BA334D may be reset to zero from the
safe area. Any switch may be used but a
Zener barrier is required to transfer the contact
closure into the hazardous area. Any one of
the diode return barriers specified on the
system certificate is suitable for this application
and this may be combined with the supply
barrier so that only one package is required.
Fig 2 illustrates how the BA334D may be reset
from both the safe and the hazardous area.
Note: The BA334D can be programmed to
reset the total display to zero when the up and
down push-buttons are operated
simultaneously for more than two seconds. –
see 6.12