Siemens SIPART PS2 Compact Operating Instructions page 22

Basic device "Ex i" (FF)
Note
Only the certified circuits may be connected as auxiliary power supply, control and signal circuits.
Figure 13 Electrical connection for the intrinsically safe version of the standard controller
Connection of device with type of protection "Ex nA", "Ex nL" and "Ex tD" (HART and PA)
Basic device, Ex n (HART)
+
Figure 14 Two-wire connection, Zones 2 and 22 "Ex n"
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SIPART PS2 (6DR5...)
A5E03436620-01, 03/2011