3
1. DESCRIPTION
The BA304C is an intrinsically safe loop powered
digital indicator which displays the current flowing
in a 4/20mA loop in engineering units. The
indicator introduces less than 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 main application of the BA304C is to display a
measured variable or control signal in a hazardous
process area. The zero and span of the display are
independently adjustable so that the indicator may
be calibrated to display any variable represented
by the 4/20mA current, e.g. temperature, flow,
pressure or level.
The BA304C has been certified intrinsically safe by
ITS Testing and Certification Ltd to the European
ATEX Directive 94/9/EC. The EC-Type
Examination certificate specifies that under fault
conditions the voltage, current and power at the
two input terminals will not exceed those specified
for simple apparatus.
Safety approvals from other authorities allowing
installation outside Europe are described in
appendices to this manual.
The indicator is available in a glass reinforced
polyester (GRP), or an epoxy painted aluminium
enclosure. Both provide IP66 protection.
2. OPERATION
Fig 1 shows a simplified block diagram of a
BA304C. 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 analogue to digital
converter and liquid crystal display. 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 BA304C
3 INTRINSIC SAFETY CERTIFICATION
3.1 ATEX certificate
The BA304C has been issued with an EC-Type
Examination Certificate number ITS02ATEX2027
by Notified Body ITS Testing and Certification Ltd.
This confirms compliance with the European ATEX
Directive for Group II, Category 1G equipment,
EEx ia IIC T5. The instrument bears the
Community Mark and, subject to local codes of
practice, may be installed in any of the European
Economic Area (EEA) member countries. i.e.
Austria, Belgium, Denmark, Finland, France,
Germany, Greece, Ireland, Italy, Luxembourg,
Norway, The Netherlands, Portugal, Spain,
Sweden and the United Kingdom. ATEX
certificates are also accepted in Iceland,
Liechtenstein, Switzerland and the Czech
Republic.
This manual describes installations which conform
with BS EN60079:Part 14 Electrical Installation in
Hazardous Areas. When designing systems for
installation outside the UK the local Code of
Practice should be consulted.
3.2 4/20mA input
In Europe, sources of energy which do not
generate more than 1.5V; 100mA, 20µJ and 25mW
are for intrinsic safety purposes considered to be
simple apparatus.