KROHNE OPTITEMP TT 50 C-R EN - Manual (Page 20)

4
ELECTRICAL CONNECTIONS
20
OPTITEMP TT 50 C/R
www.krohne.com 09/2010 - 4000636502 - MA OPTITEMP TT 50 C/R R03 en
To calculate the maximum cable length for the output circuit, determine the total resistance of
the output loop (load resistance + approximate cable resistance). Find out the capacitance of the
cable being used. In the following tables you can find the maximum cable length based on the
typical values for 1 mm
2 cables. CN is the abbreviation for "Capacitance Number" which is
multiple of 5000 pF present in the device.
For multiple connections (multidrop mode), the following formula shall be used:
L = [(65 x 10 6 ) / (R x C)] x (Cn x 5000 + 10000) / C
with
L: cable length [m or ft]
R: load resistance (incl. the resistance of any Zener barrier) + cable resistsance [Ω]
C: cable capacitance [pF/m or pF/ft]
Cn: number of transmitters in the loop
1 Cable length [m]
2 Cable length [ft]
3 Load resistance and cable resistance
4 200 pF per m/ft
5 150 pF per m/ft
6 100 pF per m/ft
.book Page 20 Monday, September 13, 2010 5:07 PM