BEKA BA307E-SS, Руководство пользователя

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1. DESCRIPTION
These rugged panel mounting, intrinsically safe 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
BA307E-SS 4 digits 15mm high
BA327E-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 gas or dust
hazardous process area. The indicators are
intrinsically safe with a rugged stainless steel case
allowing them to be installed in an Ex e, Ex p, or Ex t
panel enclosure without invalidating the panel
enclosure certification. 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.
Notified Body Intertek Testing and Certification Ltd
have certified both models intrinsically safe for use in
gas and dust hazardous areas and confirmed that the
front of both instruments comply with Ex e, Ex p and
Ex t ingress and impact requirements. The intrinsic
safety EC-Type Examination certificate specifies that
under fault conditions the output voltage, current and
power at the 4/20mA input terminals will not exceed
those specified for
simple apparatus in Clause 5.7
of EN 60079-11, which simplifies installation and
documentation.
For international applications both models have IECEx
gas and dust certification which is described in
Appendix 2.
For applications in the USA and Canada both models
have FM and cFM gas certification, see 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
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