BEKA BA524D, Manual

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1. DESCRIPTION
The BA524D is a 4½ digit loop powered digital
indicator which displays the current flowing in a
4/20mA loop in engineering units. The indicator
only introduces a 1.1V drop which allows it to be
installed into almost any 4/20mA current loop. No
additional power supply or battery is required.
The BA524D is a third generation instrument
which, although having additional features
including a separate terminal compartment,
remains electrically compatible with the original
BA524 and BA524C.
The main application of the BA524D 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 instrument is housed in a robust IP66 glass
reinforced polyester (GRP) enclosure with an
armoured glass window.
2. OPERATION
Fig 1 shows a simplified block diagram of a
BA524D. 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.
Fig 1 Simplified block diagram of BA524D
Each time a 4/20mA current is applied to the
instrument, initialisation is performed. After a short
delay the following display sequence occurs:
-1.8.8.8.8 Display test in which all
segments of the display
are activated for 0.5
seconds.
Blank display For 0.5 seconds.
Decimal points For 3 seconds.
cycled
Input current Using calibration
display in information stored in
engineering instrument memory.
units.
2.1 Controls
The BA524D is controlled and calibrated via four
push-button switches which are located behind the
instrument control cover, or as an option on the
instrument cover. In the display mode i.e. when
displaying a variable, these switches have the
following functions:
P While this button is pushed the indicator
will display the input current in mA, or
as a percentage of the instrument span
depending upon how the indicator has
been programmed. When the button is
released the normal display in
engineering units will return. The
function of this push-button is modified
when alarms or a tare function are fitted
to the indicator.
Down While this button is pushed the indicator
will display the number which the
indicator has been calibrated to display
with a 4mA input. When released the
normal display in engineering units will
return.
Up While this button is pushed the indicator
will display the number which the
indicator has been calibrated to display
with a 20mA input. When released the
normal display in engineering units will
return.
E No function in the display mode.
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