5. CONFIGURATION AND CALIBRATION
The BA558E is configured and calibrated via the
four front panel push buttons that are located
below the display.
All the configuration functions are contained in an
easy to use menu that is shown diagrammatically
in Fig 8. Each function is summarised in section
5.3 which includes references to more detailed
information. Although this simple menu driven
system enables most adjustments to be made
without repeated reference to this manual, it is
recommended that at least the summary of the
configurable functions in section 5.3 is read before
attempting configuration or recalibration.
When the instrument is fitted with alarms, the basic
menu is expanded to include the alarm functions
that are described in section 9.3 of this manual.
Note:
While the instrument is being configured or
calibrated totalisation is suspended, any flow
occurring during this time will not be
recorded.
5.1 Calibration structure
Fig 7 shows the BA558E calibration structure. The
4/20mA input current, which in flow applications
represents flow rate, is usually displayed on the six
digit plus sign rate display. If necessary this flow
signal may be linearised using the square root
extractor or the 16 segment lineariser which are
selectable in the instrument’s ‘FunC’ block. The
rate display may then be calibrated using the
'CAL' or 'SEt' functions to show the flow rate in the
required linear engineering units. Both the zero
(display at 4mA) and the span (display at 20mA)
are adjustable, although for flow application the
display at 4mA is usually zero. The position of
the decimal point in the rate display is defined by
the ‘dP’ function. To simplify calibration the
BA558E uses floating point arithmetic, moving the
rate display decimal point position will therefore
affect totalisation.
For bi-directional flow applications zero flow will be
represented by an input current other than 4mA.
When one of the two bi-direction functions in the
‘FunC’ sub-menu is selected, input currents below
that representing zero flow will be shown as a
negative flow rate and the total flow display will
count down. For input currents above that
representing zero flow will be shown as a positive
flow rate and the total flow display will count up.
The BA558E total display is calculated from the
rate display using two serial factors: the timebase
't-bA5E' and the total scaling factor '5CALE-t'. The
timebase divides the rate display according to
whether the rate display represents flow per
second, per minute or per hour. The total scaling
factor '5CALE-t' is a wide range configurable
dividing factor allowing the rate and total displays
to be in different units.
For example, if a BA558E is displaying rate in litres
per minute, setting '5CALE-t' to 4.5461 produces a
total display in UK gallons. Alternatively, setting
'5CALE-t' to 4546.1 will produce a total display in
thousands of UK gallons.
The total is calculated and the display updated
once per second, which defines the resolution of
the total flow display. When total alarms are used
for batching applications, this resolution may define
the accuracy of the system.
Fig 7 Calibration structure
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