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Intrinsic Safety – Ex ‘i’a and Ex ‘i’b (Refer to BS EN 60079-11:2012) 309
INTRINSIC SAFETY – EX ‘I’A AND EX ‘I’B (REFER TO BS EN
60079-11:2012)
Where circuits are required purely for the transmission of signals, data, logic or
instructions, the energy in the circuit can be limited to level below which ignition
of explosive vapours/gases cannot occur. However, the circuits must also be pro-
vided with barriers which will prevent any faults from allowing these limits to be
exceeded. The barriers can utilise zenor diode circuits to blow a fuse, or can convert
the galvanic signal to an optical signal using ‘opto-isolators’. The ignition curves for
a resistive circuit are given in Fig. 5.4.1.
FIGURE 5.4.1
Ignition curves for a resistive circuit.
