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1. DESCRIPTION
These panel mounting, general purpose 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 enclosures.
Model Display Bezel size
BA507E
4 digits 15mm high
96 x 48mm
BA527E
5 digits 11mm high
96 x 48mm
and bargraph.
BA508E
4 digits 34mm high
144 x 72mm
BA528E
5 digits 29mm high
144 x 72mm
and bargraph.
This instruction manual supplements the
instruction sheet supplied with each instrument.
The main application of all the models is to display
a measured variable or control signal in a 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.
The BA507E, BA527E, BA508E and the BA528E
are not certified for use in explosive atmospheres.
For hazardous area applications the BA307E,
BA327E, BA308E or the BA328E should be used.
2. OPERATION
Fig 1 shows a simplified block diagram of all the
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
