KROHNE OPTITEMP TT 31 R EN - Manual (Page 15)

02/2011 – 4000753501 – MA OPTITEMP TT31CR R01 en www.krohne.com
15
4.5 Cable length
ATTENTION!
In the Ex version, please note that the maximum cable length is determined by all of the
cable parameters.
The total capacitance and inductance of the cable must be within the limits for the
transmitter described in the Ex certificate.
To calculate the maximum cable length for the output circuit, determine the total
resistance of the output loop (load resistance plus the approximate cable resistance).
Find out the cable capacitance of the cable being used.
In the case of additional capacitance and inductance of the sensor, these values must be
subtracted from C
0
/ from L
0
.
To calculate the maximum cable length, the Ex data must be used.
Input (terminals 11 ... 14, 21 ... 24, intrinsically safe sensor terminals)
I
0
= 13 mA
L
0
= 100 mH
C
0
= 550 nF
Calculation (L
max
:is indicated in meters)
L
max
= C
0
/C Value C
0
from the Ex data, C = cable capacitance / m
L
max
= L
0
/L Value L
0
from the Ex data, L = cable inductance / m
Important note!
Use the smaller of the two calculated values as the maximum cable length.