1. DESCRIPTION
These rugged 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 two models are electrically similar, but have
different displays.
Model Display
BA507E-SS
4 digits 15mm high
BA527E-SS
5 digits 11mm high
and 31 segment bargraph.
This instruction manual supplements the instruction
sheet supplied with each instrument.
The main application of both models is to display a
measured variable or control signal in a process area.
The indicators have a rugged stainless steel case with
IP66 front of panel ingress and impact protection
allowing them to be installed in environments where
they are liable to be impacted. 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 input current, e.g.
temperature, flow, pressure or level.
2. OPERATION
Fig 1 shows a simplified block diagram of both
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
3
