RKI Instruments GD-70D Series - Manual (Page 18)

2 Installation 2-1. Requirements
GD-70D - 18 -
Introducing protective measures against lightning
If cables are installed outside the factory/plant, or if internal cables are installed in the same duct as the
cables coming from outside the factory/plant, "lightning" will cause problems. Because lightning acts as a
large emission source while cables act as a receiving antenna, devices connected to the cables may be
damaged.
Lightning cannot be prevented. Cables installed in a metal conduit or under the ground cannot be
completely protected from inductive lightning surge caused by lightning. Although complete elimination of
disasters caused by lightning is impossible, the following protective measures can be taken.
Protection against
lightning Take appropriate measures in accordance with the importance of the facilities
and the environment.
• Connect the transmission signal route by using optical fiber.
• Provide protection by a lightning arrester (cable safety retainer).
(Although inductive lightning surge can be transmitted through the cable, it is
prevented by installing a lightning arrester before the field devices and central
processing equipment. For information on how to use a lightning arrester, please
contact the manufacturer.)
Grounding In addition to lightning, there are more sources of surge noise. To protect devices from
these noise sources, the devices must be grounded.
* The lightning arrester has a circuit to remove a surge voltage which damages field devices, so that
signals may be attenuated. Before installing a lightning arrester, verify that it works properly.
Proper use of alarm contact
The alarm contact of the detector is used to transmit signals to activate an external buzzer, alarm lamp or
rotating lamp. Do not use the detector for controlling purpose (e.g., controlling the shutdown valve).
The specifications for the alarm contact of the detector are based on the resistant load conditions. If
inductive load is used at the alarm contact, the following errors will occur easily because counter
electromotive force is generated at the contact.
• Deposition, defective insulation or defective contact at the relay contact
• Damage of any electric parts due to high-voltage generated inside the detector
• Abnormal operations by an out-of-control CPU
If load is to be activated, appropriate measures must be taken to stabilize the operation of the detector and
protect the alarm contact referring to the following information.
• Relay it with an external relay at a lower voltage of 100 VAC or below (contact amplification). At the same
time, the surge absorbing part SK1 suitable for the specifications must be attached to the external relay.
• In addition, the surge absorbing part SK2 must be attached to the loaded side of the external relay if
necessary.
• It may be recommended that the surge absorbing part should be attached to the contact for certain load
conditions. It must be attached to an appropriate position by checking how the load is activated.
CAUTION
• The b contact (break contact) under de-energized state may be opened momentarily by a physical
shock, such as external force.
• When the b contact is selected for the alarm contact, take appropriate actions to prepare for a
momentary activation, for example, add signal delay operation (approximately one second) to the
receiving side of the b contact.
CAUTION
• In principal, do not activate inductive load at the alarm contact of the detector. (In particular, never use
the inductive load to activate a fluorescent lamp or motor.)
• If inductive load is activated, relay it with an external relay (contact amplification). However, because
the coil of an external relay also involves inductive load, select a relay at a lower voltage (100 VAC or
below), and then protect the contact of the detector with an appropriate surge absorbing part, such as
a CR circuit.