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Fieldbus Standard IEC 61158-2

Bus-types for 31.25 kbit/s – 100 Ω (e.g. PROFIBUS PA, Foundation Fieldbus)
Parameter Type A Type B Type C Type D
Impedance at f = 31.25 kHz 100 ± 20 Ω 100 ± 30 Ω not specified not specified
Max. conductor resistance 24 Ω/km 56 Ω/km 132 Ω/km 20 Ω/km
Max. attenuation at f = 39 kHz 3.0 dB/km 5.0 dB/km 8.0 dB/km 8.0 dB/km
Max. capacitance unbalance to shield 2 nF/km not specified not specified not specified
Max. capacitance unbalance not specified 6 nF/km length ≥ 30 m not specified not specified
Nom. conductor cross-section 0.8 mm2 0.32 mm2 0.13 mm2 1.25 mm2
Max. propagation delay change 1.7 μs/km not specified not specified not specified
Min. shield coverage 90 % not specified not specified not specified
Max. usable length including all spur cables 1,900 m 1,200 m 400 m 200 m

Type A is the preferred bus type nowadays.

Type A is a single pair cable with an overall shield and is made to meet the high demand of automation engineering. Belcom also offers multipair individually screened cables wherein each pair fulfils type A requiremensts acc. to IEC 61158-2.

Type B is an alternative type also used.

Type B is a version consisting of several pairs and an overall shield. Please note the restricted characteristics which can have a detrimental effect in case of future extensions of the plant.

Types C and D are of little importance and have been included here for the sake of completeness only.


Bus for impendance range – 100 Ω up to 220 Ω (e.g. PROFIBUS DP).

For bus use in impedance range between 100 Ω and 220 Ω, IEC61158-2 defines cable types A and B with the following characteristics:

Parameter Type A Type B
Characteristic impedance Characteristic impedance 100–130Ω at f >100 kHz
Conductor resistance (loop) 110 Ω/km not specified
Minimum conductor cross-sectional 0.34 mm2 0.22 mm2

The cable consists of one pair and an overall shield and the preferred type is type A.

Fiber optic cables

In addition to copper cables, fibre optic cables consisting of the following fibre types defined according to IEC 61158-2 are used:

Multi mode fibre - 62.5/125 µm

Single mode fibre - 9...10/125 µm as well as

Plastic fibre - 980/1000 µm

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