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non-hazardous area hazardous area

control room
DEHNpipe
BLITZDUCTOR XT DPI MD EX 24 M2
Ex(i) isolator BXT ML4 ... EX
+ BXT BAS EX FISCO
3’ 4’ EX 24 BXT ML4 BD 4 3
1’ protected 2’ BLITZDUCTOR 2 1
Ex zone 1, 2 Ex zone 0
min. 4 mm 2

Figure 9.32.4 Surge protective devices in an intrinsically safe measuring circuit

Figure 9.32.5 Surge protective devices for intrinsically safe measuring circuits

the field line which extends beyond the building must have Other selection criteria for surge protective devices
the same discharge capacity as the surge protective device in intrinsically safe measuring circuits
installed on the tank. Downstream of the surge protective de-
vice, the intrinsically safe line is led via an isolating amplifier Insulation strength of equipment
(Figure 9.32.5). From there, the shielded line to the LPC is To ensure that leakage currents do influence the measured
routed in LPZ 2. The cable shield is connected on both ends, values, the sensor signals from the tank are frequently gal-
therefore no surge protective device is required at the transi- vanically isolated. The insulation strength of the transmitter
tion from LPZ 1 to LPZ 2 since the electromagnetic residual between the intrinsically safe 4 … 20 mA current loop and
interference to be expected is significantly attenuated by the the earthed temperature sensor is ≥ 500 V a.c. Thus, the equip-
cable shield earthed on both ends (see also “Shield treatment ment is unearthed. When using surge protective devices, this
in intrinsically safe measuring circuits”). unearthed state must not be interfered with.

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