18
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.
6.17 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.
7. CALIBRATION EXAMPLES
This section includes two examples illustrating how
a BA354ND 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 7.1 describes the preferred method of
calibration using a traceable 4/20mA calibrator.
Section 7.2 contains an example of calibration
using the instruments internal 4 and 20mA
references, which although not traceable, are
adequate for many industrial applications.
7.1 Calibration example
Using an external current source
In this example the BA354ND rate totaliser is
connected to a flowmeter having an output of
20mA at a flow of 1100 litres / minute. The
BA354ND 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 operating mode the BA354ND is required to
display the input current as a percentage of span
when the
P
push-button is operated.
Step 1
Connect instrument to calibrator
Connect the BA354ND 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.
