4
Full Description of Switch Functions
P
While this button is pushed the rate
display will show the input current in
mA, or as a percentage of the
instrument span depending upon how
the instrument has been programmed.
When the button is released the
normal display in engineering units will
return. The function of this push-button
may be modified when alarms are
fitted to the instrument.
Down
While this button is pushed the
instrument will show the calibrated rate
display with 4mA input - usually zero
for flow applications. When the button
is released the flow rate will again be
displayed.
Up
While this button is pushed the
instrument will show the calibrated rate
display with 20mA input. When the
button is released the flow rate will
again be displayed.
E
While these buttons are pushed the
+Down
total display will show the least
significant eight digits of the grand
total, and the grand total annunciator
will be activated.
E
+
Up
While these two buttons are pushed
the total display will show the most
significant eight digits of the grand
total and the grand total annunciator
will be activated.
Down
Resets the total display to zero
+Up
when these two push-buttons are
operated simultaneously.
Selectable function from programme
menu.
See section 5.15
2.2 Displays
The BA554D has two digital displays and
associated annunciators, plus a flow indicator
as shown on page 1.
Rate
Shows the flow rate on the smaller
Display
five digit display.
Total
Shows the total flow since the
display
instrument was last reset on the
larger eight digit display.
Flow
This disc in the lower left hand corner
indicator
of the display 'rotates' when the input
current exceeds 4mA.
3. SYSTEM DESIGN
3.1 Flow transmitter loops
A BA554D rate totaliser may be connected in
series with any 4/20mA flow loop and calibrated
to display the rate of flow and total flow in
engineering units. Fig 2 illustrates a typical flow
loop application. The 4/20mA loop must be
able to tolerate the additional 1.1V required to
operate the BA554D.
Fig 2 BA554D in a flow loop
Considering the example shown in Fig 2, the
sum of the maximum voltage drop introduced by
each component in the loop must be less than
the minimum power supply voltage.
Min operating voltage of 2-wire flowmeter
10.0
Maximum voltage drop caused by controller
5.0
Maximum voltage drop caused by BA554D
1.1
Maximum voltage drop caused by cables
0.4
_____
16.5V
At 20mA the power supply must therefore have
an output greater than 16.5V
3.2 Remote indication
The BA554D rate totaliser may be driven from
any 4/20mA signal to provide a remote
indication of rate and total flow. Fig 3 shows a
typical application in which the 4/20mA output
from a flowmeter drives a remote BA554D.
Again it is necessary to ensure that the 4/20mA
loop is able to supply the 1.1V required to
operate the BA554D.
