4. How to Use
4-3. Precautions for system designing
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* The lightning arrester has a circuit to remove a surge voltage which damages field devices, so that
signals may be attenuated by installing the arrester. Before installing a lightning arrester, verify that it
works properly.
Proper use of alarm contact
The alarm contact of the gas detector is used to transmit signals to activate the alarm lamp, rotating lamp,
etc. Do not use it for controlling purpose (e.g. controlling the shutdown valve).
The specifications for the alarm contact of the gas detector are based on the resistance 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 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 gas 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 principle, do not activate inductive load at the alarm contact of the gas detector. (In particular,
never use the inductive load to activate a fluorescent lamp, motor, etc.)
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 detector with an appropriate surge
absorbing part, such as a CR circuit.
