12
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 two least 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 repeat
step 5.
Step 6
With 20.000mA input current adjust
the span potentiometer until the
indicator displays 140.0
Step
7
Repeat steps 5 and 6 until both
calibration points are correct.
8.4 Display backlights
The BA304ND may be supplied with two different
backlights. The loop powered backlight produces
green background illumination enabling the display
to be read at night and in poor lighting conditions.
No additional power supply or field wiring are
required, but the indicator voltage drop is
increased. Alternatively, the separatly powered
backlight has a bright orange output which
enhances daylight viewing, but additional field
wiring and a power supply are required.
8.4.1 Separately powered backlight
The separately powered backlight is electrically
segregated from the measuring circuit, and has
been certified as a separate Ex nL Group II,
Category 3G circuit.
The Type nL input safety parameters are:
Ui
=
30V dc
Ii
=
100mA dc
Pi
=
1.3W
This allows the backlight to be powered from a
safe area 18 to 30V dc supply as shown in Fig 8.
Providing the supply voltage is less than 30V dc,
the backlight safety components will ensure that
the maximum input current and power are within
the safety limits.
Reducing the supply voltage below 18V, or fitting a
current limiting resistor in series with the supply will
reduce the display brilliance.
Fig 8 Separately powered backlight
8.4.2 Loop powered backlight
This backlight is connected in series with the
4/20mA measuring circuit as shown in Fig 9. In
normal operation the voltage and current applied to
terminals 1 and 13 of the BA304ND must not
exceed:
Ui
=
6V dc
Ii
=
30 mA dc
Providing the maximum input current in normal
operation is less than 30mA, the maximum voltage
between the indicator terminals will automatically
be limited by the internal safety components.
