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4.3.4 Optional 4/20mA output
The BA364D can be supplied with an isolated
4/20mA current sink which may be programmed
to produce an analogue output proportional to
any part of the speed display. See section 4.7
4.3.5
Optional alarm outputs
The BA364D can be supplied with two isolated
solid state alarm outputs which may be
independently programmed as high or low, speed
or run-time alarms with normally open or normally
closed outputs. These outputs may be used to
switch certified intrinsically safe devices within
the hazardous area, or the contacts may be
transferred to the safe area via a Zener barrier.
See section 4.6
4.4 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 BA364D 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 the isolators that
may be used and defines the maximum permitted
cable parameters.
Fig 4.2 illustrates the basic circuit that is used for
all BA364D tachometer 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 run-time display is not used, or is reset from
the instrument front panel only the power supply
galvanic isolator is required.
Fig 4.2 Basic tachometer circuit using isolators
4.4.1 Power supply
The BA364D galvanic isolator system certificate
lists a wide range of certified galvanic isolators
that may be used to power the instrument. If
using the entity concept to select an isolator, in
addition to matching the safety parameters, the
isolator must be capable of supplying 10V dc
minimum at 15mA to the BA364D.
4.4.2 Input
When the BA364D 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
1000
100Hz
3 & 4
Proximity
detector
1.2mA
2.1mA
5kHz
3 & 4
Open
collector
2k
10k
5kHz
3 & 4
Magnetic
pick-off
0mV
20mV
peak
5kHz
3 & 4
Voltage
pulse
1.0V
3.0V
5kHz
3 & 4
The intrinsic safety requirements are explained in
section 1.4.3 Almost any mechanically or
magnetically activated switch, or intrinsically safe
NAMUR 2-wire proximity detector may be directly
connected to the input terminals.
If the BA364D is located in a hazardous area but
the transducer is in a safe area, a galvanic
isolator is required to transfer the transducer
output to the instrument. The system certificate
defines devices which may be used.
