3
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.
Both models are electrically similar, but have
different size displays.
Model
Display
BA504G-SS-PM
4 digits 34mm high
in stainless steel
enclosure.
BA524G-SS-PM
5 digits 29mm high with
31 segment bargraph.
in stainless steel
enclosure.
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 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 BA504G-SS-PM and the BA524G-SS-PM are
not certified for use in explosive atmospheres. For
hazardous area applications, the BA304G-SS-PM,
or the BA324G-SS-PM should be used.
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
