BEKA BA304NG, Руководство пользователя

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1. DESCRIPTION
These field mounting, Ex nA and Ex tc certified
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 size displays.
Model Display
BA304NG 4 digits 34mm high
BA324NG 5 digits 29mm 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 Zone 2
gas hazardous area or in a Zone 22 dust
hazardous 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.
Both models have Ex nA and Ex tc certification
issued by Notified Body Intertek Testing and
Certification Ltd which has been used to confirm
compliance with the European ATEX Directive
2014/34/EU.
For international applications both models have
IECEx certification which is described in
Appendix 2.
For applications in the USA and Canada, both
models have ETL and cETL certification which is
described in Appendix 3.
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