Vaisala LT31, Руководство пользователя, Страница: 76 / 294

User's Guide ______________________________________________________________________
76 __________________________________________________________________ M210667EN-C
The recommended AC wire cross sections and typical cable diameters for
AC voltage 230VAC are shown in Table 7 below. A copper cable with
a 5 % voltage drop has been used. For the voltage of 115VAC, the
maximum distances should be divided by four. The maximum power
consumption of LT31 is 800 W.
Table 7 AC Cable Selection for LT31
Maximum
Distance from
Voltage Source One Wire Cross-section
Area Nearest AWG
Gauge
2 km 10 mm
2
No 7 AWG
3 km 16 mm
2
No 5 AWG
4.5 km 25 mm
2
No 3 AWG
NOTE Cables with diameters more than 15 mm require a separate junction box.
Vaisala TERMBOX-1200/TERMBOX-9000 is recommended.
Communication Cable
The customer must provide cables and conduits. The cables used for the
transmission of digital and low-level analogue signals should be of the
following kind. All field cables should be armored, suitable for
underground use, and led to the equipment through conduits. Unless the
cables are armored, they have to be led through pipes. The signal cable
shields should be grounded at both ends.
For the intercommunication between the LT31 transmitter and receiver
two screened 2 x 0.22 mm
2
(approximately AWG 23) twisted pair signal
cables with a shield and minimum diameter of 8 mm are recommended.
For modem and RS signal cable, use a screened 2 x 0.22 mm
2
(approximately AWG 23) twisted pair signal cable with a shield and
minimum diameter of 8 mm. If the modem line length exceeds 50 km,
consult Vaisala.
If RS-485 connections are used, pay special attention to the quality of the
cable. The shield should be continuous, in other words, also connected to
the distribution frames.
The interface enclosure has a data cable outlet for cable diameters of 8 to
11 mm. This is reserved for signal or modem cables. The optional
AC/data cable outlet can also be used for data cables. The cable should
be led out from the unit inside the lower mast section. Grounding must be
done within the cable gland in order to keep the EMI levels within
specifications.