4 How to Use
4-3. Precautions for system designing
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SD-2600
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 units
from these noise sources, the units 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 gas monitor is used to transmit signals to activate an external buzzer, an alarm
lamp or a rotating lamp. Do not use the gas monitor for controlling purpose (e.g., controlling the shutdown
valve.)
The specifications for the alarm contact of the gas monitor 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 gas monitor
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 gas monitor
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
In principle, do not activate inductive load at the alarm contact of the gas monitor. (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 gas monitor with an appropriate surge absorbing part, such
as a CR circuit.
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.
