3
1. DESCRIPTION
The BA554D is a 4/20mA loop-powered rate
totaliser primarily intended for use with
flowmeters. The instrument simultaneously
displays the rate of flow represent by the
4/20mA input current and the total flow in
engineering units on two separate displays. The
BA554D 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 IP66 glass reinforced
polyester (GRP) enclosure with an armoured
glass window, the BA554D 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
BA554D. 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 BA554D
2.1 Controls
The BA554D 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
display 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 8.2
