16
To gain access to the security code link, remove
the instrument control cover by undoing the two
'C' screws - see Fig 4. If the instrument is fitted
with external push-buttons the connecting ribbon
cable should be un-plugged. The security
code override link is located on the inner row of
the five pin connector as shown in Fig 8.
5.17 Over and under-range
If the rate display range is exceeded the four
least significant digits will be blanked. Under-
range is indicated by a flashing ‘-1’ and over-
range by a flashing ‘1’. Under and over-range
will also be indicated if the input current falls
below approximately 3.6mA or rises above
approximately 21mA.
If the input current falls below approximately
3mA the instrument initialisation sequence is
performed as described in section 2.
When the total display exceeds 99999999 it will
automatically roll-over to zero and continue
counting. If this is likely to happen the grand
total should be reset at the start of the operation,
the most significant eight digits of the grand total
will then indicate how many times the total
display has rolled-over. The most significant
eight digits of the grand total can be viewed by
pressing the
E
and
Up
buttons simultaneously
Up to 108 roll-overs can be counted.
6. CALIBRATION EXAMPLES
This section includes two examples illustrating
how a BA554D rate totaliser may be
programmed and calibrated to display the rate of
flow and total flow measured by a flowmeter with
a 4/20mA output. Section 6.1 describes the
preferred method of calibration using a traceable
4/20mA calibrator. Section 6.2 contains an
example of calibration using the instruments
internal 4 and 20mA references, which although
not traceable, are adequate for many industrial
applications.
6.1 Calibration example
Using an external current source
In this example the BA554D rate totaliser is
connected to a flowmeter having an output of
20mA at a flow of 1100 litres / minute. The
BA554D is required to display flow in litres per
minute and total flow in cubic metres with a
resolution of 0.1 cubic metres. Totalisation is to
occur for flow rates between 1 and 100% of
maximum flow. The frequency of the mains
supply is 50Hz and a security code of 1209 is
required. In the display mode the BA554D is
required to show the input current as a
percentage of span when the
P
push-button is
operated.
Step 1
Connect instrument to calibrator
Connect the BA554D to an accurate
current source such as a calibrator.
Terminal 1 positive and terminal 3
negative. The instrument will
perform the initialisation routine
described in section 2, and then
display the input current on the rate
display using the existing calibration
information.
Step 2
Enter the programming mode
With input current between 4 and
20mA put the instrument in the
programming mode by
simultaneously pressing
P
and
E.
Assuming a security code has not
already been entered the instrument
will respond by displaying 'root'
which is the first function in the main
menu. See Figs 7A and 7B.
Step 3
Turn square root extractor off
With 'root' displayed, press
P
which
will reveal the root extractor status.
The root extractor can be turned on
or off by operating the
Up
or
Down
buttons. Select 'OFF', and press
E
to return to the 'root' prompt in the
main menu.
