16
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.
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 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.
6. CALIBRATION EXAMPLES
This section includes two examples illustrating how
a BA558C 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 BA558C 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 BA558C rate totaliser is
connected to a flowmeter having an output of
20mA at a flow of 1100 litres / minute. The
BA558C 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 BA558C 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 BA558C 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.
