Siemens 353 User Manual page 170

Installation
TEMPERATURE
Maintain the temperature of the air surrounding an operating controller below 50°C (122°F). Check air
temperature periodically to ensure that this specification is not being exceeded.
Exceeding the specified operating temperature limits can adversely affect
performance and may cause damage to the controller.
Forced air ventilation is recommended when controllers are mounted in a partially or completely enclosed panel or
cabinet (e.g. NEMA 1); as shown at right. When clean air is present, exhaust fans are often mounted across the top
of a panel and louvers formed in the panel bottom. Air is then drawn upward between the station cases. When air
contains particulate matter, fans and filters are generally located at the panel bottom and louvers at the top. Filtered
air is now forced upward between the station cases. Filters must be serviced periodically.
Only high quality, quiet running fans should be used.
Also, the fans should not generate electrical noise
which could interfere with electronic instruments.
A sealed cabinet (e.g. NEMA 12 or 4X) housing 353s
must not contain other equipment that generates
significant heat and must contain a fan to force air to
flow around equipment and throughout the cabinet
preventing hot spots from developing. Forced air
conditioning may be required in high density panels or
consoles. Periodically change or clean air filters.
CONTAMINANTS
The controller case is slotted to permit circulation of
clean cooling air. Liquids and corrosive gases must
not be allowed to enter the case. Whether the
controller is in a control room or field mounted it must
be protected from rain, air conditioning condensate,
and plant and process related fluids and gases.
Extended exposure to contaminants can result in
malfunctions.
Industrial environments often contain airborne
particulate contaminants. Particulate matter, usually
dust and dirt, is abrasive and can cause intermittent
connections. A layer of dust on circuit boards can
interfere with component heat dissipation and can
absorb other airborne contaminants. Extended
exposure to these contaminants may result in
malfunctions.
Although 353 boards have a protective coating, the
following steps can reduce contaminant related
equipment malfunctions:
7-2
CAUTION
Instrument
X03102S0
Air Inlet
No. of Fans: One for each 16 stations or 3 ft. of panel width.
Air Inlet: 30 in² for each fan. If filters are used, they must
be changed periodically (increase inlet to 50 in²).
Forced Air Ventilation for Enclosed Panels
UM353-1B
Fan with
Finger
Guard
Air Outlet
Enclosed
Panel
April 2012