VACUUBRAND DVR 4S - Manual (Page 11)

page 11 of 20
Documents are only to be used and distributed completely and unchanged. It is strictly the users´ responsibility to check
carefully the validity of this document with respect to his product. manual-no.: 99 90 72 / 13/08/2005
Calculation example for the connection of an intrinsically safe circuit to the DVR 4S
Do not exceed the max. permitted capacity and inductance of the intrinsically safe circuit (according to
corresponding standards).
1 Maximum values for the intrinsically safe circuit defined in the standard (depending on connected
components):
C
max
= 110 nF
L
max
= 5 mH
2 Subtract the effective maximum capacities and inductances of the connected devices, e. g. DVR 4S:
C
max´
= 110 nF - 64 nF = 46 nF
L
max´
= 5 mH - 60 µH = 4.9 mH
3 Calculation of the permitted cable length:
Assumed values of the cable parameters in case of non-shielded cable:
C
= 110 nF/km
L = 0.65 mH/km
Calculation with regard to the capacity:
l = (46 nF/110 nF) x 1000 m = 418 m
Calculation with regard to the inductance:
l = (4.9 mH/0.65 mH) x 1000 m = 7500 m
4 The smaller value limits the cable length:
l
max
= 400 m