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8. ACCESSORIES
8.1 Engraved scale and tag plates
All BA304NC indicators are fitted with blank
stainless steel scale and tag plates above and
below the display. These can easily be removed
for engraving, or if requested they can be supplied
engraved with any units of measurement and tag
information. Each plate can accommodate:
1 row of 9 alphanumeric characters 10mm
high.
or 1 row of 11 alphanumeric characters 7mm
high.
or 2 rows of 18 alphanumeric characters 5mm
high.
8.2 Root extractor
The BA304NC can be supplied with a square root
extractor which enables the indicator to accurately
display the output from a differential flow meter in
linear engineering units between 10 and 100% of
full flow (4.16 to 20mA). The root extractor
continues to operate with reduced accuracy down
to 2.5% of maximum flow, or clip-off can be
selected which will force the display to zero at
flows below 5% (4.04mA). The location of the clip-
off link is shown in Fig 7.
Fig 7 Location root extractor clip-off link
When calibrating a root extracting BA304NC the
indicator zero potentiometer should be adjusted to
give the required display at 10% of flow (4.16mA).
The indicator zero potentiometer should not be
used to set the display to zero with a 4mA input.
Zero suppression or elevation may not be used,
i.e. 4mA must correspond to zero flow.
For reference, the following table shows the output
current from a non-linearised differential flowmeter.
% of full flow Current output mA
2.5
4.01
10.0
4.16
25.0
5.00
50.0
8.00
75.0
13.00
100.0
20.00
8.2.1 Calibration example with root extractor
The BA304NC is required to display rate of flow in
gallons per minute, with a resolution of 0.1 gallons.
The differential flowmeter has an output of 20mA
at a flow rate of 140.0 gallons per minute.
i.e. A span of 1400 ignoring the decimal point
A decimal point in position 00.0
The following adjustments are required:
Step 1
Put the suppression / elevation links in
the elevation position.
Step 2
Put the zero link in the 0 to 500
position.
Step 3
The required span is 1400, therefore
the span links should be placed in the
1000 to 1500 position.
Step 4
The decimal point is required between
the least two significant digits, therefore
the decimal point link should be placed
in the 00.0 position.
Step 5
With 4.160mA input current adjust the
zero potentiometer until the indicator
displays 14.0 (10% of flow). If there
is insufficient adjustment to achieve
this, put the elevation/suppression links
in the suppression position and
continue with the calibration procedure.
