3
1. DESCRIPTION
The BA354D is an intrinsically safe 4/20mA loop-
powered rate totaliser primarily intended for use
with flowmeters. The instrument simultaneously
displays the rate of flow and the total flow in
engineering units on two separate displays. The
BA354D only introduces a 1.1V drop which allows
it to be installed into almost any 4/20mA flow loop.
No additional power supply or battery is required.
The BA354D has been certified intrinsically safe by
European Notified Body Intertek Testing Sevices
(ITS) to the ATEX Directive 94/9/EC for use in
explosive gas and combustible dust atmospheres.
The EC-Type Examination Certificate specifies that
under fault conditions the voltage, current and
power at input terminals 1 and 3 will not exceed
those specified for
simple apparatus
in Clause 5.4
of EN50020:1994.
ATEX dust certification is an option – See
Appendix 1.
Housed in a robust IP66 glass reinforced polyester
(GRP) enclosure with an armoured glass window,
the BA354D is surface mounting, or may be pipe
mounted using one of the accessory kits. A stem
mounting kit is also available allowing direct
mounting onto a flowmeter conduit entry.
2. OPERATION
Fig 1 shows a simplified block diagram of a
BA354D. 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. After a short
delay the following display sequence occurs:
All segments of the display are activated for
about 3 seconds.
Decimal points on large display are
sequentially activated for about 3
seconds.
Rate display and totaliser start to
function
using calibration information
stored in the instrument's permanent
memory.
If the 4/20mA current is disconnected during
operation the latest total and grand total are stored
in permanent memory.
Fig 1 Simplified block diagram of BA354D
2.1 Controls
The BA354D is controlled and calibrated via four
push-button switches which are located behind the
instrument control cover, or as an option on the
outside of the instrument cover. In the operating
mode i.e. when the instrument is displaying rate
and total flow the switch functions are:
Summary of Switch Functions
P
Displays input current in mA or as a
percentage of span.
Down
Shows rate display calibration at 4mA
input
Up
Shows rate display calibration at
20mA input
E+Down
Grand total –
displays least significant 8 digits
E+Up
Grand total –
displays most significant 8 digits.
Down
Resets total display
+Up
programmable function
Note
: When optional alarms are fitted the push-
buttons may be programmed to have alternative
functions – see section 9.2
