BEKA BA307NE, Руководство пользователя

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1. DESCRIPTION
These panel mounting, Ex nA certified non-
sparking 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
BA307NE 4 digits 15mm high
BA327NE 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 Zone 2
gas hazardous area or a Zone 22 dust hazardous
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.
If required optional factory fitted dual alarms and a
green display backlight which can be loop or
separately powered, should be specified when the
instrument is ordered.
Both models have been issued with a common
Type Examination Certificate ITS14ATEX48028X
by Notified Body Intertek Testing and Certification
Ltd. This confirms compliance with the type of
protection requirements for non-sparking Ex nA
apparatus, and for dust ignition protection by
enclosure Ex tc. This certificate has been used to
confirm compliance with the European ATEX
Directive 94/9/EC.
T
he certificate number has an 'X' suffix indicating
that the two indicators are subject to special
condition for safe use. For installations in Zone 2
the panel enclosure into which the indicators are
mounted should comply with Ex n requirements
which are defined in BS EN 60079-15. The
indicators may also be installed in an Ex e or Ex p
panel enclosure located in Zone 2 as described in
Appendix 2.
Installation requirements for use in Zone 22 dust
hazardous areas are described in Appendix 2..
The two indicators have also been issued with a
common IECEx Ex nA and Ex tc Certificate of
Conformity which is described in Appendix 3.
For applications in the USA and Canada, both
models have ETL and cETL certification which is
described in Appendix 4.
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 less than 1.2mA the indicator
will display the error message ‘LPLo’, below this
input current the instrument will not function
correctly.
Fig 1 Indicator block diagram