Fieldbus Standard IEC 61158-2
| 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