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4.2 SYSTEM
The basic system used for all BA364ND
hazardous area tachometer installations is shown
in Fig 4.1 Ex nL certification requirements are
explained in section one of this manual which
should be read before the system is designed.
Fig 4.1 Tachometer installation using barriers
4.2.1 Power supply
A BA364ND must be powered from the safe
area. To comply with certification requirements
the maximum supply voltage in normal operation
must be less than 30V, but greater than 10V
which is the minimum operating voltage of the
BA364ND.
When operating as a tachometer the BA364ND
consumes approximately 12mA plus, if used, the
current for one proximity detector.
4.2.2 Input
When the BA364ND is programmed as a
tachometer only input A is operational. This input
may be 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 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
3 & 4
Proximity
detector
1.2mA
2.1mA
5kHz
3 & 4
Open
collector
2k
Ω
10k
Ω
5kHz
3 & 4
Magnetic
pick-off
0mV
20mV
peak
5kHz
3 & 4
Voltage
pulse
1.0V
3.0V
5kHz
3 & 4
The certification requirements are explained in
section one. Almost any mechanically or
magnetically activated switch, Type n NAMUR 2-
wire proximity detector or voltage pulse may be
directly connected to the input terminals.
4.2.3 Resetting the run-time display
In addition to resetting the run-time display by
operating the
Up+Down
push buttons, the display
may also be reset by connecting terminals 7 & 8
together for at least one second. To achieve
reliable resetting the contacts must close for at
least one second.
Any switch located in the hazardous area as
shown in Fig 4.1 may be used for resetting.
4.2.4 Options
When the BA364ND is programmed as a
tachometer, optional alarms and an optional
isolated 4/20mA current output may be fitted.
The function of these options is described in
sections 4.4 & 4.5 and the Ex nL certification
requirements in section 1 of this manual.
