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1. DESCRIPTION
The BA358C 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 BA358C 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 BA358C has been certified intrinsically
safe by European Notified Body Intertek
Testing Sevices (ITS) to the ATEX Directive
94/9/EC. 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.
Safety approvals from authorities outside
Europe are being obtained, please contact
BEKA associates for the latest information.
Housed in a robust 72 x 144 panel mounting
DIN enclosure, the BA358C has an IP65
front panel which will not support a static
charge, and is supplied with a gasket to seal
the joint between the instrument and the
panel.
2. OPERATION
Fig 1 shows a simplified block diagram of a
BA358C. 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 BA358C
2.1 Controls
The BA358C is controlled and calibrated via
four front panel push-button switches. In the
display mode i.e. when the instrument is
displaying rate of flow and total flow, these
switches have the following functions:
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
