RKI Instruments GD-K71D - Manual (Page 16)

PT2E-1052
15
（３）Lightning measures
Lightning
surge
There is the problem “Lightning”. When make outdoor wiring of cable
at factory or plants etc or when make a parallel wiring in the same
duct with the cable in from outdoor even at the indoor wiring. If the
lightning is a huge generation source, the cable is a reception antenna
and there is the case that cable connecting instrument is broken. It
is impossible to prevent the generation of lightning. If the cable
should put in metal tube or laid in the underground, it is impossible to
prevent the inductive lightning surge generating from the thunder.
Lightning
measures
There is not the complete countermeasure for it but the following
method can be considered.
Make the suitable treatment accordingly.
a) The transmission signal route is arranged for connection by the
optical fiber cable etc.
b) Countermeasure by the lightning arrester (Cable safety retainer).
There is the way to install the lightning arrester just before the
field apparatus and the central control station.
Please contact with the manufacturer of lightning arrestor in
details.
Grounding
Surge noise shall be generated from the thunder lightning or except it.
To protect detector from these cause, be sure to make grounding.
＊In the lightning rod, there is the circuit to remove the surge voltage to be a cause of damage
from field instruments.
By installing the lightning rod, the signal may be attenuated. When install the lightning rod, it
is required to check the performance in advance.
（４）Alarm contact
・Alarm contacts shall be used only for external buzzer and alarm light, and do not use
it for the controlling use (such as solenoid valve control etc).
When control the external load, the bad influence may be given to the system according to
the load characteristics. In such case, the following countermeasure shall be taken to
stabilize the action and protect the contact.
・Make relay(contact amplification) with the low voltage relay and operate by connecting CR
circuit (Spark Killer: SK) (Diode etc for DC) suited for relay coil directly to relay.
・Add CR circuit to the load side of relay on the request.
CAUTION （FOR USE OF NORMALLY-CLOSED CONTACT）
Normally-closed contact (Break contact) at de-energized condition may change to
open contact in a moment due to physical shock.
Whenever alarm signals from gas detectors are used with normally-closed
contact, please put delayed-circuit (for about one second) to receiver side of
normally-closed contact to avoid such phenomenon.