Каталог Weidmuller: Electronics - Analogue Signal Conditioning

Technical appendix/Glossary
EX basics
Safety in hazardous areas
Which explosion protection categories are most commonly
used
These devices are divided into the category groups and
which differ in the number of occurring malfunctions.
W
• Pressure-resistant encapsulation (Ex d) in compliance
with EN60079-1:
Components that are capable of triggering an explosion are
enclosed in a housing that is capable of withstanding the
explosion. Openings in the housing are designed to prevent
the explosion from being transmitted externally.
• Increased safety (Ex e) in compliance with EN60079-1:
This explosion protection category is normally applied to
transformers, motors, batteries, terminal blocks, electrical
lines and cables. It is not suitable for the protection of electronic
components and spark-generating components (such as
switches, relays or surge protection). Additional measures
and an increased safety level are implemented in order to
prevent any sparks, electrical arcing or unallowable high
temperatures which could trigger ignitions. Increased safety
is made by possible by housing that prevents dusts from
penetrating within.
• Explosion protection methods (Ex n):
This explosion protection category may only be used in the
hazardous areas 2/22. Here there is no danger of an explosion
from the electrical equipment during normal operations or
during defined malfunctions. This includes all elec trical
devices and components that have no spark-forming
contacts and that have a water-proof or dust-proof housing.
Larger creepage and clearance distances are not required
as long as the maximum rated voltage of 60 V AC / 70 V DC
is maintained.
• Intrinsic safety (Ex i) in compliance with EN60079-11:
Power supply to the electrical equipment is carried out
through a safety barrier which functions to limit the current
and voltage so that the minimum power and temperature
levels for creating an explosive mixture are not reached.
Intrinsic safety for electrical and electronic devices is specified
so that their circulating or stored power (even in event of
malfunction) is never strong enough to trigger an explosion
in an explosive atmosphere. You must also remember that
not only the electrical device but also all other components
connected to the circuit may be exposed to the explosive
atmosphere. All switching circuits in intrinsically safe devices
must be designed so that they are also intrinsically safe.
Category
=> Switching circuits within category electrical devices
must not be able to cause a spark even if two independent
malfunctions take place.
Category
=> Switching circuits in electrical devices must not be able to
cause a spark when a malfunction.
Electrical devices for use in explosive gas, vapour and
mist atmospheres – in accordance with CENELEC
Explosion protection type Identification
Pressure-resistant Ex d
encapsulation
Protective design
Encloses the explosion and prevents fire
from spreading
Increased safety Ex e No spark formation or hot surfaces
Method of explosion protection Ex n No spark formation or hot surfaces
Intrinsic safety Ex i Limited energy for preventing spark formation
or overheated surface temperatures
CENELEC classification of gases, dusts and the
maximum permitted surface temperatures of devices
and components
Gas
Temperature classes
group T1 T2 T3 T4 T5 T6
I Methane - - - - -
IIA Ammonia Ethyl alcohol Benzene, Acetaldehyde - -
Methane
Ethane
Propane
Cyclohexane
n-Butane
n-Hexane
Kerosene
IIB Lighting Ethylene, Ethylene Ethyl ether - -
gases,
Acrylonitrile
Ethylene
oxide
glycol,
Hydrogen
sulphide
IIC Hydrogen Ethine
(Acetylene)
- - - Hydrocarbons
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