4
ELECTRICAL CONNECTIONS
24
TT 51 SERIES
www.krohne.com
08/2015 - 4000754203 - MA TT 51 R03 en
4.7 Connection diagram of rail-mount transmitter (intrinsically safe)
4.8 Cable length
In order to ensure reliable HART
®
communication, the maximum cable length of the output
circuit must be observed.
To calculate the maximum cable length for the output circuit, determine the total resistance of
the output loop (load resi 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.
Figure 4-4: Connection diagram
1
Input (intrinsically safe)
2
Classified hazardous area (potentially explosive area e.g. zone 0, 1 or 2)
3
Classified hazardous area (potentially explosive area e.g. zone 1 or 2)
4
Safe area
5
Modem / Ex (intrinsically safe)
6
R
Load
(intrinsically safe)
7
Voltage supply 10
…
30 VDC (intrinsically safe - terminals 21, 22)
Field device
Cable insulation
PVC
Polyethylene
Polyethylene foam
[m]
[ft]
[m]
[ft]
[m]
[ft]
1 (CN = 1)
600
1969
1100
3609
2000
6562
10 Multidrop (CN = 1)
500
1640
900
2953
1600
5249
10 Multidrop (CN = 4.4)
85
279
150
492
250
820
Table 4-1: Maximum length for typical 1 mm
2
cables
Insulation
Capacitance [pF/m]
PVC
300...400
Polyethylene
150...200
Polyethylene foam
75...100
MA_OPTITEMP_TT_51_en_150828_4000754203_R03.book Page 24 Friday, August 28, 2015 10:54 AM
