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LCD and plasma screens are no longer just the remit of the front room and bedroom. There is just as much chance of seeing a LCD TV on the high street these days than in a living room as outdoor digital signage and open air entertainment systems are spreading throughout our cities and towns.

There are many reasons for taking an LCD TV outdoors. For signage and advertising an outdoor TV system will obviously reach a larger audience while for entertainment, TV systems are more and more likely to be placed outside as customers choose to spend the evenings in the open air due largely to the introduction of the smoking bans.

Standard LCD TVs are obviously not designed for outdoor use but that doesn't meant that they can't be used outside and while specific outdoor LCD TVs are available their cost can be prohibitive to most businesses.

Fortunately a far more cost effective but just as protective solution is available in the guise of an LCD enclosure. These are a really flexible solution as they allow the use of standard TV systems in outdoor and hazardous locations. An LCD enclosure allows the use of standard TVs because it protects against the outdoor elements and when any LCD TV is placed outside these elements need to be considered.

Water

Rainfall and water splashing is perhaps the biggest threat to an outdoor TV system or LCD placed in an industrial location. Ensuring the LCD stays dry and is sealed against water ingress is important which is why just as outdoor LCD TV's are built to IP65 and NEMA 4 so is an LCD enclosure, making it waterproof.

Dust and airborne particles

Not much of a consideration for outdoor use but a higher level of airborne particulates are present in outdoor locations but it is a real problem in industrial applications which is why LCD enclosures are dustproof.

Extreme temperature

Both the screen and LCD may experience a heat wave or cold snap which is why thermostatic cooling and heating systems are installed in LCD enclosures and the screens are protected using anti-glare glass.

Richard N Williams is a technical author and a specialist in the digital signage industry helping to develop outdoor digital signage and protection for plasmas. Please visit us for more information about LCD Enclosures or other digital signage solutions.

Ultra high vacuum

Concepts involved

Advanced Definition

Kinetic theory of gases

Gas transport and pumping

Vacuum pumps and systems

Typical uses for ultra high vacuum

Ultra high vacuum is necessary for many surface analytic techniques such as:

X-ray photoelectron spectroscopy (XPS)

Auger electron spectroscopy (AES)

Secondary ion mass spectrometry (SIMS)

Thermal desorption spectroscopy (TPD)

Thin film growth and preparation techniques with stringent requirements for purity, such as molecular beam epitaxy (MBE) and UHV chemical vapor deposition (CVD)

Angle resolved photoemission spectroscopy (ARPES)

UHV is necessary for these applications to reduce surface contamination, by reducing the number of molecules reaching the sample over a given time period. At 0.1 mPa (106 Torr), it only takes 1 second to cover a surface with a contaminant, so much lower pressures are needed for long experiments.

UHV is also required for:

Particle accelerators

Atomic physics experiments which use cold atoms, such as ion trapping or making Bose-Einstein Condensates

Achieving ultra high vacuum

Extraordinary steps are required to reach UHV, including the following:

High pumping speed possibly multiple vacuum pumps in series and/or parallel

Minimize surface area in the chamber

High conductance tubing to pumps short and fat, without obstruction

Use low-outgassing materials such as certain stainless steels

Avoid creating pits of trapped gas behind bolts, welding voids, etc.

Electropolish all metal parts after machining or welding

Use low vapor pressure materials (ceramics, glass, metals, teflon if unbaked)

Bake the system (250 C to 400 C) to remove water or hydrocarbons adsorbed to the walls

Chill chamber walls to cryogenic temperatures during use

Avoid all traces of hydrocarbons, including skin oils in a fingerprint always use gloves

Outgassing is a significant problem for UHV systems. Outgassing can occur from two sources: surfaces and bulk materials. Outgassing from bulk materials is minimized by careful selection of materials with low vapor pressures (such as glass, stainless steel, and ceramics) for everything inside the system. Even materials which are not generally considered absorbent can outgas, including most plastics and some metals. For example, vessels lined with a highly gas-permeable material such as palladium (which is a high-capacity hydrogen sponge) create special outgassing problems.

Outgassing from surfaces is a subtler problem. At extremely low pressures, more gas molecules are adsorbed on the walls than are floating in the chamber, so the total surface area inside a chamber is more important than its volume for reaching UHV. Water is a significant source of outgassing because a thin layer of water vapor rapidly adsorbs to everything whenever the chamber is opened to air. Water evaporates from surfaces too slowly to be fully removed at room temperature, but just fast enough to present a continuous level of background contamination. Removal of water and similar gases generally requires baking the UHV system at 200 to 400 C while vacuum pumps are running. During chamber use, the walls of the chamber may be chilled using liquid nitrogen to reduce outgassing further.

Hydrogen and helium are the most common background gases in a well-designed, well-baked UHV system. Hydrogen diffuses out from the grain boundaries in stainless steel. Helium can diffuse through the steel and glass from the outside air.

Typically, there is no single vacuum pump that can operate all the way from atmospheric pressure to ultra high vacuum. Instead, a series of different pumps is used, according to the appropriate pressure range for each pump. Pumps commonly used to achieve UHV include:

Turbomolecular pumps (especially compound and/or magnetic bearing types)

Ion pumps

Titanium sublimation pumps

Non-evaporable getter (NEG) pumps

Cryopumps

UHV pressures are measured with an ion gauge, either a hot filament or an inverted magnetron type.

Finally, special seals and gaskets must be used between components in a UHV system to prevent even trace leakage. Nearly all such seals are all metal, with knife edges on both sides cutting into a soft, copper gasket. This all-metal seal can maintain pressures down to 100 pPa (~1012 Torr).

Measuring high vacuum

Main article: Pressure measurement

Measurement of high vacuum is done using a nonabsolute gauge that measures a pressure-related property of the vacuum, for example, its thermal conductivity. See, for example, Pacey. These gauges must be calibrated. The gauges capable of the measuring the lowest pressures are magnetic gauges based upon the pressure dependence of the current in a spontaneous gas discharge in intersecting electric and magnetic fields.

UHV manipulator

A UHV manipulator allows an object which is inside a vacuum chamber and under vacuum to be mechanically positioned. It may provide rotary motion, linear motion, or a combination of both. The most complex devices give motion in three axes and rotations around two of those axes. To generate the mechanical movement inside the chamber, two basic mechanisms are commonly employed: a mechanical coupling through the vacuum wall (using a vacuum-tight seal around the coupling), or a magnetic coupling that transfers motion from air-side to vacuum-side. Various forms of motion control are available for manipulators, such as knobs, handwheels, motors, stepping motors, piezoelectric drives, and pneumatics.

The manipulator or sample holder may include features which allow additional control and testing of a sample, such as the ability to apply heat, cooling, voltage, or a magnetic field. Sample heating can be accomplished by electron bombardment or thermal radiation. For electron bombardment, the sample holder is equipped with a filament which emits electrons when biased at a high negative potential. The impact of the electrons bombarding the sample at high energy causes it to heat. For thermal radiation, a filament is mounted close to the sample and resistively heated to high temperature. The infra-red energy from the filament heats the sample.

References and notes

^ DJ Pacey (W. Boyes, editor) (2003). Measurement of vacuum; Chapter 10 in Instrumentation Reference Book (Third Edition ed.). Boston: Butterworth-Heinemann. p. 144. ISBN 0750671238. http://books.google.com/books?id=sarHIbCVOUAC&pg=PA144&lpg=PA144&dq="measurement+of+vacuum"&source=web&ots=aWbFsOCsvf&sig=NcVTpfYXN5X-8STfeOIIKeCG0EU#PPA144,M1. 

^ LM Rozanov & Hablanian, MH (2002). Vacuum technique. London; New York: Taylor & Francis. p. 112. ISBN 041527351X. http://books.google.com/books?id=8yEGJCtS2XgC&pg=PA79&lpg=PA79&dq="measurement+of+vacuum"&source=web&ots=RmEYhDyVOY&sig=Muaslx8-GZW6zWBCa403si5cuRM#PPA112,M1. 

^ LM Rozanov & Hablanian, MH. p. 95. ISBN 041527351X. http://books.google.com/books?id=8yEGJCtS2XgC&pg=PA79&lpg=PA79&dq="measurement+of+vacuum"&source=web&ots=RmEYhDyVOY&sig=Muaslx8-GZW6zWBCa403si5cuRM#PPA95,M1. 

See also

Vacuum engineering

Vacuum flange

Vacuum gauge

Journal of Vacuum Science and Technology

Vacuum

Vacuum state

External links

American Vacuum Society

Three major steps to get Ultra High Vacuum

Vacuum Systems and Thin-Film Technology Course

CERN Ultra high vacuum solar thermal collector.

Categories: Vacuum
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91 acura integra questions?

The car is a 91 integra gs. B18a1, 1.8L dohc, 1834cc. I can go on all day with specs. When I bought it the guy had put a nguyen? Exhaust on the car. Stainless steel. Looks like 2-2.5" from the exhaust manifold back. Has echo chamber after the cat. It had a blown head gasket. I took the head off, pressure check, resurfaced, valves and seals were good. Replaced the whole gasket set, arp head studs, bosh platinum+4 plugs, wires, new lifters, rockers, timing belt, I'm running royal purple oil and filter. When I was finished, I droved it for maybe 200 miles(not straight). When I went to have it inspected it failed horribly. So I took it to a shop and the guy said my 02 sensor isnot even working and he said the cat isn't getting hot enough. He thinks its just a resinator. That there's no catalyst inside. Just looks like a cat. It doesn't blow smoke when I'm idling but I was told it smokes when I am driving it. Any thoughts.

If the O2 sensor is the original it is definitely time to replace it. They start getting sluggish around the 100K mile mark (Bosch says 60K but they like selling sensors) and after 20 years yours is probably like a 20 year old hound dog.

I can easily believe the previous owner gutted the catalytic converter. Nice guy. Putting a new one on there and replacing the sensor has a good chance of getting the emissions in line, but it is also a good idea to clean the EGR too. The previous owner obviously scoffed about emission compliance so I'm sure he never had the EGR cleaned.

Arista Corporation -- Showcases Their NEMA 4X-Dedicated Panel PC Series, Plus a Brief NEMA 4/4X Industry Discussion
FREMONT, CA--(Marketwire - July 7, 2010) - Arista Corporation , www.goarista.com , leader in the design and development of Industrial Computers, is showcasing their NEMA 4X-dedicated series of panel PCs.

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