6
Fig 2 BA326C in a transmitter loop
4.2
Remote indication
A BA326C may be driven via an intrinsically
safe interface from a 4/20mA safe area signal
to provide a remote indication within a
hazardous area.
The type of interface is not
critical, either a Zener barrier or a galvanic
isolator may be used, providing that the
BA326C Ui, Ii and Pi are not exceed.
If one side of the 4/20mA current loop may be
earthed, a single channel Zener barrier
provides the lowest cost protection.
If the
4/20mA signal is not isolated, then two Zener
barriers, a two channel Zener barrier or a
galvanic isolator must be used.
When the hazard is a IIC gas, and two single
channel Zener barriers or a two channel Zener
barrier are used, only one barrier or channel
may be a 28V; 93mA; 300ohm device. Again
it is necessary to ensure that the voltage
capability of the 4/20mA signal is sufficient to
drive the indicator plus the voltage drop
introduced by the intrinsically safe interface.
Figs 3A, 3B and 3C show the alternative
circuits which may be used.
Fig 3A Simplest circuit with one side of
4/20mA current loop connected
to
earth.
Fig 3B Two Zener barrier channels are
required if the 4/20mA current loop
can not be earthed at the barrier
busbar.
Summary of Contents for ba326c
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