BEKA BA524D, Manual

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3. APPLICATIONS
3.1 Transmitter loops
The BA524D indicator may be connected in series
with any 4/20mA current loop that can tolerate the
1.1V drop required to operate the instrument, and
be calibrated to display the measured variable or
control signal in engineering units.
Fig 2 illustrates a typical application in which a
BA524D indicator is connected in series with a
2-wire transmitter.
Fig 2 BA524D in a transmitter loop
Considering the example shown in Fig 2, the sum
of the maximum voltage drops of all the compo-
nents in the loop must be less than the minimum
power supply voltage.
Minimum operating voltage of 2-wire Tx 10.0
Maximum voltage drop caused by controller 5.0
Maximum voltage drop caused by BA524D 1.1
Maximum voltage drop caused by cables 0.4
_____
16.5V
Therefore at 20mA the power supply in this
example must have an output greater than 16.5V
3.2 Remote indication
A BA524D indicator may be driven from any
4/20mA signal to provide remote indication. Fig 3
shows a typical application in which the output from
a gas analyser drives a BA524D. Again it is neces-
sary to ensure that the voltage capability of the
4/20mA gas analyser output is greater than the
sum of voltage drops introduced by the BA524D
and the cable resistance.
Fig 3 Remote indication
4. INSTALLATION
4.1 Location
The BA524D indicator is housed in a robust IP66
glass reinforced polyester (GRP) enclosure incor-
porating an armoured glass window and stainless
steel fittings making it suitable for exterior mount-
ing in most industrial installations, including
off-shore and waste water treatment.
The BA524D is surface mounting, but may be pipe
or stem mounted using the accessory kits
described in sections 8.7 and 8.8 of this manual.
The field terminals and the two mounting holes are
located in a separate compartment with a sealed
cover allowing the instrument to be installed
without exposing the display assembly.
Terminals
2 and 4 are internally joined and may be used for
linking the return 4/20mA wire - see Fig 2.
Similarly terminals 5 and 6 are internally joined and
may be used for linking cable screens. The
BA524D earth terminal is connected to the internal
EMC filters. For maximum radio frequency inter-
ference rejection this terminal should be connected
to a local earth, or to an earthed cable screen.
To
prevent circulating currents, cable screens should
only be earthed at one point.
The BA524D enclosure is fitted with a bonding
plate to ensure electrical continuity between the
three conduit / cable entries.
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