11
8. ACCESSORIES
8.1 Engraved scale and tag plates
All BA304C 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
etched 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 Internal Calibrator
The BA304C can be supplied with an optional
internal calibrator which simulates 4 and 20mA
input currents. This allows rapid calibration without
the need for external instruments or disconnection
from the 4/20mA input current, but it is not a
substitute for calibration with a traceable external
current source. Fig 6 shows the position of the
calibrator link.
An internal calibrator can not be fitted to an
instrument with a root extractor.
To recalibrate the BA304C using the internal
calibrator, the following procedure should be
followed. This may be done at any input current
between 4 and 20mA.
Step 1
Put the suppression / elevation, zero,
span and decimal point links in the
required position.
Step
2
Put the calibrator link in the 4mA
position and adjust the indicator zero
potentiometer to give the required
display at 4mA.
Step 3 Put the calibrator link in the 20mA
position and adjust the indicator span
potentiometer to give the required
display at 20mA.
Step
4 Repeat steps 2 and 3 until both
calibration points are correct. The span
and zero controls are almost
independent so it should only be
necessary to repeat each adjustment
twice.
Step
5
Return the calibrator link to the
'indicate' position. The indicator will now
respond to the 4/20mA input current
with the revised calibration.
8.3 Root extractor
The BA304C 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 lineariser 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 BA304C 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
A root extractor can not be fitted to an instrument
with an internal calibrator.