Edwards Signaling Catalog
Gas Groups (plus dusts and fibers) There are two main gas groups, Group I– Mining only and Group II– Surface Industries These categories are used in European and I.E.C. groupings. Group I is concerned only with underground mining where methane and coal dust are present. Group II gases occurring in surface industries, are sub-grouped according to their volatility. This enables electrical equipment to be designed to less onerous tolerances if it is to be used with the least volatile gases. Temperature Hot surfaces can ignite explosive atmospheres. To guard against this, all electrical equipment intended for use in a potentially explosive atmosphere is classified according to the maximum surface temperature it will reach in service. This temperature is normally based on a surrounding ambient temperature of 40C° (102°F). This temperature can then be compared to the ignition temperature of the gas(es) which may come into contact with the equipment and a judgement reached as to the suitability of the equipment to be used in that area. Typical gas/material European/I.E.C. Gas Group North American Gas Group Methane I – Acetylene IIC A Hydrogen IIC B Ethylene IIB C Propane IIA D Metal dust – E Coal dust – G Grain dust – G Temperature Classification European/I.E.C. North American Maximum Surface Temperature T1 T1 450° C T2 T2 300° C T2A 280° C T2B 260° C T2C 230° C T2D 215° C T3 T3 200° C T3A 180° C T3B 165° C T3C 160° C T4 T4 135° C T4A 120° C T5 T5 100° C T6 T6 85° C Types of Electrical Equipment Suitable for use in Potentially Explosive Atmospheres Different techniques are used to prevent electrical equipment from igniting explosive atmospheres. There are restrictions on where these different types of equipment can be used as follows: European Area of use Designation Standard IEC Area of use Designation Standard NEC Area of use Designation Standard Flameproof Enclosure– An enclosure used to house electrical equipment, which when subjected to an internal explosion will not ignite a surrounding explosive atmosphere. Zones 1 & 2 EExd EN60079-1 Zones 1 & 2 Exd IEC60079-1 Class I, Divisions 1 & 2 – UL1203 Intrinsic Safety– A technique whereby electrical energy is limited such that any sparks or heat generated by electrical equipment is sufficiently low as to not ignite an explosive atmosphere. Zones 0, 1 & 2 EExi EN50020 Zones 1 & 2 Exi IEC60079-11 Class I, Divisions 1 & 2 – UL913 Increased Safety– This equipment is so designed as to eliminate sparks and hot surfaces capable of igniting an explosive atmosphere. Zones 1 & 2 EExe EN60079-7 Zones 1 & 2 Exi IEC60079-7 – – – Purged and Pressurized– Electrical equipment is housed in an enclosure which is initially purged to remove any explosive mixture, then pressurised to prevent ingress of the surrounding atmosphere prior to energization. Zones 1 & 2 EExp EN50016 Zones 1 & 2 Exp IEC60079-2 Class I, Divisions 1 & 2 – NFPA496 Encapsulation– A method of exclusion of the explosive atmosphere by fully encapsulating the electrical components in an approved material. Zones 1 & 2 EExm EN60079-18 Zones 1 & 2 Exm IEC60079-18 – – – Oil Immersion– The electrical components are immersed in oil, thus excluding the explosive atmosphere from any sparks or hot surfaces. Zones 1 & 2 EExo EN50015 Zones 1 & 2 Exo IEC60079-6 Class I Division 2 – UL698 Powder Filling– Equipment is surrounded with a fine powder, such as quartz, which does not allow the surrounding atmosphere to come into contact with any sparks or hot surfaces. Zones 1 & 2 EExq EN50017 Zones 1 & 2 Exq IEC60079-5 – – – Non-sparking– Sparking contacts are sealed against ingress of the surrounding atmosphere, hot surfaces are eliminated. Zone 2 EExn EN60079-15 Zone 2 Exn IEC60079-15 – – – TM www.edwardssignaling.com 19
TM Science of Light Physical Principles of Light Gamma Rays X-Rays Ultraviolet Rays Infrared Rays Radar FM TV Shortwave AM 1 x 10 -14 1 x 10 -12 1 x 10 -8 1 x 10 -4 1 x 10 -2 1 x 10 2 1 x 10 4 Wavelength (in Meters) Visible Light 4 x 10 -7 5 x 10 -7 6 x 10 -7 7 x 10 -7 Wavelength (in Meters) High Energy Low Energy The electromagnetic spectrum covers an extremely broad range, from radio waves with wavelengths of a meter or more, down to x-rays with wavelengths of less than a billionth of a meter. Optical radiation (visible light) is only a small portion of this spectrum positioned between radio waves and x-rays. That portion of the spectrum that the eye can see is rather small, covering approximately 360 to 830 nm. The colors we perceive depend on wavelength, while the amount of light energy detected by the eye at a particular wavelength determines the perceived intensity of that color. In quantifying that energy, we use what is called “radiant flux”, a measure in watts, of the energy per second (or power) radiated from a source. Radiated optical energy (light) can be measured and correlated with human vision. Photometric versus radiometric measurement Photometry is the science of the measurement of light in terms of its perceived brightness to the human eye. The eye’s response to light depends on physical, physiological and psychological factors and varies from person to person, making it difficult to define the average observer. In 1924, the Commission Internationale de l’Eclairage (CIE), or International Commission on Illumination, conducted a series of experiments to quantify the human eye’s response to visible light. The result: a specified spectral luminous efficiency function V (λ) to characterize the daylight vision of the average human observer. This is now commonly known as the photopic function. Because the response changes at low light levels, the CIE also defined a scotopic function V’(λ) to characterize the response of the dark-adapted eye. As such, it takes into account the eye's sensitivity to varying degrees of light and focuses primarily on the visible light spectrum. 20 www.edwardssignaling.com
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TM<br />
Science of Light<br />
Physical Principles of Light<br />
Gamma<br />
Rays<br />
X-Rays<br />
Ultraviolet<br />
Rays Infrared Rays Radar FM TV Shortwave AM<br />
1 x 10 -14 1 x 10 -12 1 x 10 -8 1 x 10 -4 1 x 10 -2 1 x 10 2 1 x 10 4<br />
Wavelength (in Meters)<br />
Visible Light<br />
4 x 10 -7 5 x 10 -7 6 x 10 -7 7 x 10 -7<br />
Wavelength (in Meters)<br />
High Energy<br />
Low Energy<br />
The electromagnetic spectrum covers an extremely broad<br />
range, from radio waves with wavelengths of a meter or more,<br />
down to x-rays with wavelengths of less than a billionth of a<br />
meter. Optical radiation (visible light) is only a small portion of<br />
this spectrum positioned between radio waves and x-rays.<br />
That portion of the spectrum that the eye can see is rather<br />
small, covering approximately 360 to 830 nm. The colors we<br />
perceive depend on wavelength, while the amount of light<br />
energy detected by the eye at a particular wavelength<br />
determines the perceived intensity of that color. In quantifying<br />
that energy, we use what is called “radiant flux”, a measure in<br />
watts, of the energy per second (or power) radiated from a<br />
source. Radiated optical energy (light) can be measured and<br />
correlated with human vision.<br />
Photometric versus radiometric measurement<br />
Photometry is the science of the measurement of light in<br />
terms of its perceived brightness to the human eye. The eye’s<br />
response to light depends on physical, physiological and<br />
psychological factors and varies from person to person,<br />
making it difficult to define the average observer. In 1924,<br />
the Commission Internationale de l’Eclairage (CIE), or<br />
International Commission on Illumination, conducted a series<br />
of experiments to quantify the human eye’s response to visible<br />
light. The result: a specified spectral luminous efficiency<br />
function V (λ) to characterize the daylight vision of the average<br />
human observer. This is now commonly known as the photopic<br />
function. Because the response changes at low light levels,<br />
the CIE also defined a scotopic function V’(λ) to characterize<br />
the response of the dark-adapted eye. As such, it takes into<br />
account the eye's sensitivity to varying degrees of light and<br />
focuses primarily on the visible light spectrum.<br />
20<br />
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