BECKHOFF CX50x0 - Manual (Page 18)

Safety barriers – cross-zone circuits
14 CX50x0 units in potentially explosive areas
4.6.3 Temperature class
The temperature class is also relevant to the determination of usability. The temperature of a heated surface is
decisive for classification into the appropriate temperature class. The rule is that the next higher temperature
class includes all lower classes.
4.7 Safety barriers – cross-zone circuits
The connection of signal transducers (sensors) from zone 0 and 1 to evaluation units (fieldbus devices) from
zone 2 is subject to special conditions, which are coarsely outlined here. Only intrinsically safe circuits may be
used in zones 0 and 1.
A circuit is considered to be intrinsically safe if neither a spark nor a thermal effect can cause the ignition of a
certain explosive atmosphere. One of the most important measures when constructing intrinsically safe circuits
is the safe isolation of all intrinsically safe circuits from non-intrinsically safe circuits.
If an intrinsically safe circuit from zone 0 or 1 is to be connected to a non-intrinsically safe device in zone 2, the
circuit must be routed through a safety barrier. This ensures the adequate isolation of intrinsically safe and non-
intrinsically safe circuits. The following illustration shows an exemplary arrangement.