4. How to Use
4-3. Precautions for system designing
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4-3. Precautions for system designing
Using a stable power supply
The external output and alarm contact of the gas detector may be activated when the power is turned on,
when momentary blackout occurs, or when the system is being stabilized. In such cases, use a UPS
(uninterruptible power system), or take appropriate actions on the receiving side.
The gas detector must be provided with the following power supply.
Power supply
voltage
100 - 240 VAC (terminal voltage of the gas detector) 50/60 Hz
Supply voltage fluctuations up to ±10%
Allowed time of
momentary
blackout
Up to 500 milliseconds
(To recover from the momentary
blackout for 500 milliseconds or more,
restart the gas detector.)
Example of actions
To ensure continuous operation and
activation, install a UPS (uninterruptible
power system), etc. outside the gas
detector.
Others
Do not use it with a power supply of
large power load or high-frequency
noise.
Example of actions
Use a line filter, etc. to avoid the noise
source if necessary.
Heat radiation designing
When it is installed in the closed instrumentation panel, attach ventilation fans above and below the panel.
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 arrester).
(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 units from
these noise sources, the units must be grounded.
CAUTION
An unstable power supply and noise may cause malfunctions or false alarms.
The descriptions in this section must be reflected on the designing of a system using the gas
detector.
Careful consideration should be given to instrumentation to maintain safety even when a trouble
like disconnection of power/signal cable or unexpected malfunction or failure occurs.
CAUTION
When the internal temperature of the gas detector reaches about 60ºC, the power will be turned off.
Since the internal temperature rises to ten-odd degrees higher than the ambient temperature, take care
not to let the ambient temperature exceed 30ºC. Provide a clearance of 30 mm or more above the gas
detector to prevent a rise in the internal temperature.
