3
1.
DESCRIPTION
These field mounting, intrinsically safe digital
indicators display the current flowing in a 4/20mA
loop in engineering units. They are loop powered
but only introduce a 1.2V drop, which allows them
to be installed into almost any 4/20mA current
loop.
No additional power supply or battery is
required.
The four models are electrically similar, but have
different size displays and enclosure materials.
Model
Display
BA304G
4 digits 34mm high in
GRP enclosure.
BA304G-SS
4 digits 34mm high in
stainless steel enclosure.
BA324G
5 digits 29mm high and
31 segment bargraph
in GRP enclosure.
BA324G-SS
5 digits 29mm high and
31 segment bargraph in
stainless steel enclosure.
This
instruction
manual
supplements
the
instruction sheet supplied with each instrument.
The main application for all models is to display a
measured variable or control signal in a hazardous
process area. The zero and span of the display
are independently adjustable so that the indicator
can be calibrated to display any variable
represented
by
the
4/20mA
current,
e.g.
temperature, flow, pressure or level.
All models have been certified intrinsically safe for
use in gas and dust hazardous areas by Notified
Body Intertek Testing and Certification Ltd and
comply
with the European ATEX Directive
2014/34/EU. The EC-Type Examination certificate
specifies that under fault conditions the output
voltage, current and power at the 4/20mA input
terminals will not exceed those specified for
simple
apparatus
in Clause 5.7 of EN 60079-11, which
simplifies installation and documentation.
For international applications all models have
IECEx
certification
which
is
described
in
Appendix 2.
For applications in the USA and Canada all models
have ETL and cETL certification which is described
in Appendix 3.
2.
OPERATION
Fig 1 shows a simplified block diagram of all
models. The 4/20mA input current flows through
resistor R1 and forward biased diode D1. The
voltage developed across D1, which is relatively
constant, is multiplied by a switch mode power
supply and used to power the instrument. The
voltage developed across R1, which is proportional
to the 4/20mA input current, provides the input
signal for the analogue to digital converter.
Each time a 4/20mA current is applied to the
instrument, initialisation is performed during which
all segments of the display are activated, after five
seconds the instrument displays the input current
using the calibration information stored in the
instrument memory. If the loop current is too low
to power the instrument the indicator will display
the error message
LPLo
.
Fig 1 Indicator block diagram