Labkotec SET-1000, Инструкция по установке и эксплуатации, Страница: 13 / 14

SET-1000 D15233FE-2
Installation and Operating Instructions
Copyright © 2019 Labkotec Oy 13/14 We reserve the right for changes without notice
Appendix 2 Electrical parameters
When installing the device, make sure that the electrical values of the cable
between SET-1000 and sensor never exceed maximum electrical parameters.
The cabling between SET-1000 control unit and cable extension junction box /
cable joint must be executed as in figure 4 / 8 Extension cable should be shielded
paired twisted instrument cable.
Due to non-linear characteristics of the sensor voltage, the interaction of both,
capacitance and inductance, must be taken into account. The table below
indicates the connecting values in explosion groups IIC and IIB.
In explosion group IIA the values of the group IIB can be followed.
U
o
= 14,7 V I
o
= 55 mA P
o
= 297 mW R = 404
Ω
The characteristics of the output voltage is trapezoidal.
Max. permissible value Both Co and Lo
Co Lo Co Lo
II C 608nF 10 mH
568nF
458 nF
388 nF
328 nF
258 nF 0,15 mH
0,5 mH
1,0 mH
2,0 mH
5,0 mH
II B
3,84μF
30 mH
3,5 µF
3,1 µF
2,4 µF
1,9 µF
1,6 µF 0,15 mH
0,5 mH
1,0 mH
2,0 mH
5,0 mH
L
o
/R
o
= 116,5

H/

(IIC) and 466

H/

(IIB)
Table 2.Electrical parameters
Maximum length of the sensor cable is determined by the resistance (max. 75
Ω)
and other electrical parameters (Co, Lo and Lo/Ro) of the sensor circuit.
Example: Determing the maximum cable length
Instrument cable with following characteristics is used:
- DC resistance of a twin wire at + 20°C is approx. 81
Ω / km.
- Inductance is approx. 3
μH / m.
- Capacitance is approx. 70 nF/km
Influence of resistance Estimate for additional resistances in the circuit is 10
Ω. The max length of the
cable is then (75
Ω - 10 Ω) / (81 Ω / km) =
800 m .
The influence of inductance and capacitance of a 800 m cable is:
Influence of inductance Total inductance is 0,8 km x 3
μH/m = 2,4 mH. The sum value of the cable and
e.g. SET/OS2 sensor [Li = 30
μH] is 2,43 mH. L/R ratio is thus 2,4 mH / (75 – 10)
Ω = 37 μH/Ω, which is less than the maximum allowed value 116,5 μH/Ω.
Influence of capacitance Cable capacitance is 0,8 km x 70 nF/km = 56 nF. Combined value of the cable
and the e.g. SET/OS2 sensor [Ci = 3 nF] is 59 nF.
When compared to the values in table 2, we can summarize that above values do
not limit the use of this particular 800 m cable in explosion groups IIB or IIC.
Feasibility of other cable types and sensors for different distances can be
calculated accordingly.