6
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. 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. Fig 3
shows the alternative circuits which may be used.
Fig 3 Alternative circuits for remote indication
in a hazardous area
