7
Fig 3B Two Zener barrier channels are
required if the 4/20mA current loop
can't be earthed at the barrier
busbar. Also shows optional
resetting from hazardous area
Fig 3C Galvanic isolator may be used with
any 4/20mA current loop.
4.3 Resetting the total display
The total display may be reset to zero by an
external switch located in the safe or the
hazardous area. Fig 3A illustrates resetting
from the safe area via a single channel
diode return Zener barrier. A certified
intrinsically safe relay or certified opto-
isolator may also be used.
Fig 3B shows how the total display may be
reset by an external switch in the hazardous
area. The switch must be mechanically
operated and able to withstand a 500V dc
insulation test so that it complies with the
requirements for simple apparatus. No
Zener barrier or galvanic isolator is required.
The BA358C may also be programmed to
reset the total display to zero when the Up
and
Down buttons are operated
simultaneously -see 6.15
