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TXP-WTA_Instruction_Manual_(Rev1.3)
It is very difficult to protect against direct lightning strikes but the probability of a direct strike at any one location is
very small. Unfortunately, power line surges and electromagnetic energy in the air can induce high voltage surges
from lightning activity several miles away.
10.2.1 Antenna Grounding
Electromagnetic energy in the air will be drained to ground via any and every earth path. An earth path exists
between the antenna and the TXP-WTA Sensor Transmitter and to protect against damage, this earth path current
must be kept as small as possible.
This is achieved by providing better alternate earth paths.
It is important to ground the antenna to the same ground point as the TXP-WTA Sensor Transmitter. Antennas are
normally mounted to a metal bracket which should be grounded to the TXP-WTA Sensor Transmitter earth
connection. Surge energy induced into the antenna will be drained first by the mount's ground connection, second
by the outside shield of the coax cable to the ground connection on the radio and third by the internal conductor of
the coax cable via the radio electronics. This third earth path causes damage unless the other two paths provide a
better earth connection allowing surge energy to bypass the electronics.
When an antenna is located outside of a building and outside of an industrial plant environment, external coax surge
diverters are recommended to further minimize the effect of surge current in the inner conductor of the coax cable.
Coax surge diverters have gas-discharge element which breaks down in the presence of high surge voltage and
diverts any current directly to a ground connection. A surge diverter is not normally required when the antenna is
within a plant or factory environment, as the plant steelwork provides multiple parallel ground paths and good earth
grounding will provide adequate protection without a surge diverter.
10.2.2 Connection to Other Equipment
Surges can enter the wireless unit from connected devices, via I/O, serial or Ethernet connections. Other data
devices connected to the wireless unit should be well grounded to the same ground point as the wireless unit.
NOTE: Special care needs to be taken where the connected data device is remote from the wireless unit requiring a
long data cable. As the data device and the wireless unit cannot be connected to the same ground point, different
earth potentials can exist during surge conditions.
There is also the possibility of surge voltages being induced on long lengths of wire from nearby power cables. Surge
diverters can be fitted to the data cable to protect against surges entering the wireless unit.
The same principle applies to I/O devices is not close to the wireless unit, the risk of surge increases. Surge diverters
for I/O wiring are available to protect the wireless unit.
REV – 1.3
[34-2900-0207-4 ]
47 |
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