3
1. DESCRIPTION
The BA558C is a 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 BA558C 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.
Housed in a robust 72 x 144 panel mounting DIN
enclosure, the BA558C has an IP65 front panel
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
BA558C. 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 BA558C
2.1 Controls
The BA558C 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
Note:
When optional alarms are fitted the push-
buttons may be programmed to have alternative
functions – see section 8.3
