18
Fig 8 Location of security code override
link
To gain access to the security code link,
remove the instrument terminal block(s) by
gently pulling. Remove the six screws
securing the rear panel, and lift off the panel
which will reveal the link - see 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 are also 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. The most significant
eight digits of the grand total counter can
count the number of times the total display
rolls-over. If it is anticipated that in normal
operation the total display will exceed
99999999, the grand total should be reset to
zero during commissioning. Up to 10
8
roll-
overs can be counted.
7. CALIBRATION EXAMPLES
This section includes two examples
illustrating how a BA358C 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 an external traceable 4/20mA
calibrator. Section 7.2 contains an
example of calibration using the BA358C
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 BA358C rate totaliser is
connected to a flowmeter having an output
of 20mA at a flow of 1100 litres / minute.
The BA358C 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 BA358C 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 BA358C 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 an 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.
