Image Processing Reference
In-Depth Information
followed by two digits and an optional letter. Certain IP codes require that the device is com-
pletely sealed, which might cause problems for the antenna (detuning) and battery design. A
completely sealed device does not permit an easy access for battery change. The sealing could also
force the use of an internal antenna, i.e., inside the housing.
27.7.2 Hazardous Environments (EX)
When designing devices intended for use in potentially explosive atmospheres, special measures need
tobetakentopreventorminimizetheriskofexplosion.hismeansthatyoumustconsider
. Every possible electrical or nonelectrical source of ignition
. All potentially hazardous environments where the device could be deployed
. The different ways the device could be deployed and the technical ability of the person
using the device
To design and develop devices for hazardous environment requires long experience in the field as well
certification by a notified body. he overview provided in this chapter should thus not be considered
a cook book for safe designs.
ConformancetoanumberofstandardsisrequiredtoachieveEXcertiication.heIECEx
∗
Scheme
[] was created to facilitate international trade in equipment and services for use in explosive atmo-
spheres,whilemaintainingtherequiredlevelofsafety.heIECExSchemeisbasedontheuseof
specific international IEC Standards for type of protection of EX equipment. Since July , EX
productsthatareplacedontheEuropeanmarketmustbecertiiedtotheATEX
†
directive (ATEX
//EC) []. [].This involves the testing and assessment of such products to the latest ATEX standards.
To achieve an EX safe design, a number of principle protection concepts are applied, depending
on the applications and target hazardous area (zones).
•
Nonsparking devices: Typically applied to transformers, motors, cells, batteries, etc., but
not appropriate for equipment or components containing semiconductors. Protection
relies upon a dust/water tight enclosure to avoid tracking across live circuits.
•
Keep flammable gas out: Encapsulation (enclosing circuit in potting compound), oil
immersion, or pressurized enclosures to keep the potentially explosive atmosphere away
from the source of ignition. he downside of this approach is that it adds significant cost
and weight to your design and sacrifices accessibility and serviceability of the device.
•
Limit energy of sparks and surface temperatures: Protection relies upon an electronic
design that limits the emitted/transferred power of the device and prevents hot surfaces
above the given temperature class. his approach is commonly called Intrinsic Safety.
An IS design has built-in measures to prevent excessive heat buildup and the danger of an electric
spark. To achieve this, you need to put limitations on voltage, current, capacitance, and inductance
∗
International Electrotechnical Commission for Certification to Standards Relating to Equipment for use in Explosive
Atmospheres.
†
From the French-ATmospheres EXplosibles.
