LED light - Technical analysis

A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. Each diode is about 1/4 inch in diameter and uses about ten milliamps to operate at about a tenth of a watt. LEDs are small in size, but can be grouped together for higher intensity applications.

LED fixtures require a driver which is analogous to the ballast in fluorescent fixtures. The drivers are typically built into the fixture (like fluorescent ballasts) or they are a plug transformer for portable (plug‐in) fixtures. The plug‐in transformers allow the fixture to run on standard 120 volt alternating current (AC), with a modest (about 15 to 20 percent) power loss.

The efficacy of a typical residential application LED is approximately 20 lumens per watt (LPW). Incandescent bulbs have an efficacy of about 15 LPW and compact fluorescent (Energy saver Bulbs) are about 60 LPW, depending on the wattage and lamp type. LEDs are better at placing light in a single direction than incandescent or fluorescent bulbs.

Because of their directional output, they have unique design features that can be exploited by clever designs. LED strip lights can be installed under counters, in hallways, and in staircases; concentrated arrays can be used for room lighting.

Waterproof, outdoor fixtures are also available. Some manufacturers consider applications such as gardens, walkways, and decorative fixtures outside garage doors to be the most cost‐efficient. LED lights are more rugged and damage‐resistant than compact fluorescents and incandescent bulbs. LED lights don’t flicker.

They are very heat sensitive; excessive heat or inappropriate applications dramatically reduce both light output and lifetime. 

Uses include:

Task and reading lamps
Linear strip lighting (under kitchen cabinets)
Recessed lighting/ceiling cans
Porch/outdoor/landscaping lighting
Art lighting
Architectural lighting
Night lights
Stair and walkway lighting
Pendants and overhead
Retrofit bulbs for lamps

characteristic:

Individual LEDs are considerably more efficient; however, the lamp or fixture design is reduced by the driver and electronics. In addition, LEDs do not produce heat like incandescent bulbs.

LEDs last considerably longer than incandescent or fluorescent lighting. LEDs don’t typically burn out like traditional lighting, but rather gradually decrease in light output. Their “useful life” is defined by the Alliance for Solid‐State Illumination Systems and Technologies (ASSIST) as the time it takes until 70% of initial light output is reached, often 50,000 hours.

They are resistant to thermal and vibrational shocks and perform well when subjected to frequent on‐off cycling.

Initial Cost

The biggest limitation to LED for common residential use is the cost of manufacturing due to still‐limited production runs. Manufacturers claim production will increase considerably in the near future, further lowering prices. Currently, there is a limited number of LED fixture manufactures, but this is changing.

Retrofit bulbs range from Rs. 500/= to Rs. 2000/= for night lights and small lamps.

Operational Cost

The cost savings of LEDs can be found in smaller wattage lamps or for applications that take advantage of their longevity, such as difficult to reach places. They are also advantageous for dimmable fixtures, since dimmable fluorescents are expensive.

Installation

The small size of LED lights encourages a variety of design options. White LED lamps are available with Edison (screw‐in type) bases to retrofit existing fixtures. There are LED strips that can be used under cabinets. In addition, outdoor landscaping fixtures are available.

Cons and Pros of LED

LED lamps have many advantages over traditional lighting methods. These include:

• Low energy consumption – retrofit bulbs range from 0.83 to 7.3 Watts
• Long service life – LED bulbs can last up to 80,000 hours
• Durable – LED bulbs are resistant to thermal and vibrational shocks and turn on instantly from ‐ 40C° to 185C°, making them ideal for applications subject to frequent on‐off cycling, such as garages and basements
• Directional distribution of light – good for interior task lighting
• No infrared or ultraviolet radiation – excellent for outdoor use because UV light attracts bugs
• Safety and environmentally conscious – LEDs contain no mercury and remain cool to the touch
• Fully dimmable – LEDs do not change their color tint when dimmed unlike incandescent lamps that turn yellow
• No frequency interference – no ballast to interfere with radio and television signals
• Range of color – LEDs can be manufactured produce all colors of the spectrum without filters, they can also produce white light in a variety of color temperatures

Some disadvantages to LED lighting:

• LEDs are currently more expensive than more conventional lighting technologies, and may be hard to locate
• LED is very heat sensitive. Excessive heat or inappropriate applications dramatically reduce both light output and lifespan & create Harmonics
• LEDs typically cast light in one direction at a narrow angle compared to incandescent or fluorescent lamps so lenses or reflectors are needed in fixtures to broaden the beam (if desired)

How & Why Electro Static Discharge? (ESD)

An increasing problem today with the use of more and more electronic equipment in our systems is the Electro Static Discharge(ESD).The main source of the problem is the wrong handling of electronic components, printed circuit boards, etc.

A component damaged by ESD has been exposed to a too high voltage level and today the components are much more sensitive depending on integration, which means more functions in the same capsule. The distances between the conductors are decreased and therefore the insulation distance will be at a minimum.

A value of 0.002 mm is common in modern integrated circuits.

Electro static charge is caused in three different ways:

1. Rubbing of two surfaces to each other.
2. Separation of two surfaces from each other, for example when removing a plastic cover from its contents.
3. Induction caused by static electricity without any contact of the material.

Two type of faults and different circuits

1. The ESD damages are divided into two groups of faults: direct fault and latent defect. The direct faults are quite easy to detect since the component will not work at all and this is very often discovered at the factory before shipping.
2. The latent defects can be very difficult to identify since the component is not working in a reliable way and the life length of the device may be reduced dramatically.

Fault generated by ESD Digital circuits:

• ”Ones” becomes ”zeros” and ”zeros” becomes ”ones” for no reason.
• No ”ones” or ”zeros” at all ( the circuit is dead).

Analogue circuits:

• Worsening accuracy of measuring
• Wrong voltage levels that require adjustments
• Malfunction

Electro static voltage levels:

A voltage level of between 100-500 V can destroy any electronic components in principle. The most sensitive components can only withstand voltages between 25-170 V.

Sometimes it is possible to hear a ”click” sound when touching an object and that is typical ESD phenomena. When it is possible to hear that ”click” sound the voltage level is already at least 3,5 kV. Sometimes it is also possible to see a spark when touching an object and the voltage level is then at least 10 kV.

Below some values are given for typical Electro static charge:

• Walking on a wall-to-wall carpet: 10 – 20 kV
• Walking on a plastic floor (PVC): 2 – 5 kV
• Walking on an anti-static floor: 0 – 2 kV
• Lifting paper from a table: 5 – 35 kV
• Rising from a chair: 10 -25 kV
• Protection against ESD damages
• It is possible to reduce the risk of ESD to a minimum for the equipment.
• This is very important to remember when making service and/or repair with electronic components for example the printed circuit board on a soft starter.

Actions to prevent damages:

• Avoid charge if possible
• Always use a wrist strap or similar connected to ground potential when working with electrical components
• Always use the right type of package (ESD protected bags, etc.)
• Connect all machines and apparatus to ground potential
• High humidity

Explanation of IP Protection standard.

IP interpreted as Ingress Protection Marking, classifies and rates the degree of protection provided against intrusion (body parts such as hands and fingers), dust, accidental contact, and water by mechanical casings and electrical enclosures.

The protection of enclosures against ingress of dirt or against the ingress of water is defined in IEC60529 (BSEN60529:1991). Conversely, an enclosure which protects equipment against ingress of particles will also protect a person from potential hazards within that enclosure, and this degree of protection is also defined as a standard.

The degrees of protection are most commonly expressed as ‘IP’ followed by two numbers, e.g. IP65, where the numbers define the degree of protection. The first digit shows the extent to which the equipment is protected against particles, or to which persons are protected from enclosed hazards. The second digit indicates the extent of protection against water.

The wording in the table is not exactly as used in the standards document, but the dimensions are accurate.

IP Degree of Protection according to EN/IEC 60529

Power quality improvement with harmonic filters

In electrical plants the loads draw from the network electric power (active) as power supply source (e.g. personal computers, printers, diagnostic equipment, etc.) or convert it into another form of energy (e.g. electrical lamps or stoves) or into mechanical output (e.g. electrical motors). To get this, it is often necessary that the load exchanges with the network (with net null consumption) the reactive energy, mainly of inductive type.

This energy, even if not immediately converted into other forms, contributes to increase the total power flowing through in the electrical network, from the generators, all along the conductors, to the users. To smooth such negative effect, the power factor correction of the electrical plants is carried out.

The power factor correction obtained by using capacitor banks to generate locally the reactive energy necessary for the transfer of electrical useful power, allows a better and more rational technical-economical management of the plants.

Passive Filter

Capacitor banks can be used combined with inductors in order to limit the effects of the harmonics on a network. Actually, the combination capacitor-inductor constitutes a filter for harmonics.

To avoid the negative effects of resonance, it is necessary to insert an inductor in series with a capacitor. By applying an analogous reasoning, it is possible to think of placing in a point of the network a combination of an inductor and a capacitor properly dimensioned in order to get the same resonance frequency of the order of the current harmonic to be eliminated.

In this way, the assembly inductor-capacitor presents a very low reactance in correspondence with the harmonic to be eliminated which shall circulate in the assembly without affecting the whole network.

Therefore this filter, called passive filter, consists in a capacitor connected in series with an inductor so that the resonance frequency is altogether equal to the frequency of the harmonic to be eliminated. Passive filters, which are defined on a case by case basis, according to a particular harmonic to be filtered, are cost-effective and easy to be connected and put into function.

Active Filter

Active filters instead can automatically eliminate the current harmonics present in a network in a wide range of frequencies. Exploiting power electronic technology, they can inject a system of harmonics able to neutralise those present in the network.

The active filter has the advantage of filtering simultaneously dozens of harmonics and does not involve design costs for dimensioning.

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spider-shaped small Soft multi-functional robots !

Scientists have created a soft spider shaped robotic.  the spider is a demonstration of a new manufacturing process that can produce soft robots on the millimetre scale with micrometer-scale features for microsurgery and other procedures.

Roboticists are envisioning a future in which soft, animal-inspired robots could be safely deployed in difficult-to-access natural and human-made environments, such as in delicate surgical procedures in the human body, or in spaces too small and unpredictable to be conquered with rigid robots or too dangerous for humans to work with rigid robots in. Centimeter-sized soft robots have been created, but thus far it has not been possible to fabricate multifunctional flexible robots that can move and operate at smaller size scales.

A team of researchers at Harvard's Wyss Institute for Biologically Inspired Engineering, Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Boston University now has overcome this challenge by developing an integrated fabrication process that enables the design of soft robots on the millimeter scale with micrometer-scale features. To demonstrate the capabilities of their new technology, they created a robotic soft spider -- inspired by the millimeter-sized colorful Australian peacock spider -- from a single elastic material with body-shaping, motion, and color features. The study is published in Advanced Materials.

"The smallest soft robotic systems still tend to be very simple, with usually only one degree of freedom, which means that they can only actuate one particular change in shape or type of movement," said Sheila Russo, Ph.D., co-author of the study. Russo helped initiate the project as a Postdoctoral Fellow in Robert Wood's group at the Wyss Institute and SEAS and now is Assistant Professor at Boston University. "By developing a new hybrid technology that merges three different fabrication techniques, we created a soft robotic spider made only of silicone rubber with 18 degrees of freedom, encompassing changes in structure, motion, and color, and with tiny features in the micrometer range."

Wood, Ph.D., is a Core Faculty member and co-leader of the Bioinspired Soft Robotics platform at the Wyss Institute and the Charles River Professor of Engineering and Applied Sciences at SEAS. "In the realm of soft robotic devices, this new fabrication approach can pave the way towards achieving similar levels of complexity and functionality on this small scale as those exhibited by their rigid counterparts. In the future, it can also help us emulate and understand structure-function relationships in small animals much better than rigid robots can," he said.

In their Microfluidic Origami for Reconfigurable Pneumatic/Hydrolic (MORPH) devices, the team first used a soft lithography technique to generate 12 layers of an elastic silicone that together constitute the soft spider's material basis. Each layer is precisely cut out of a mold with a laser micromachining technique, and then bonded to the one below to create the rough 3D structure of the soft spider.

Key to transforming this intermediate structure into the final design is a pre-conceived network of hollow microfluidic channels that is integrated into individual layers. With a third technique known as injection-induced self-folding, pressurized one set of these integrated microfluidic channels with a curable resin from the outside. This induces individual layers, and with them also their neighboring layers, to locally bend into their final configuration, which is fixed in space when the resin hardens. This way, for example, the soft spider's swollen abdomen and downward-curved legs become permanent features.

"We can precisely control this origami-like folding process by varying the thickness and relative consistency of the silicone material adjacent to the channels across different layers or by laser-cutting at different distances from the channels. During pressurization, the channels then function as actuators that induce a permanent structural change," said first and corresponding author Tommaso Ranzani, Ph.D., who started the study as a Postdoctoral Fellow in Wood's group and now also is Assistant Professor at Boston University.

The remaining set of integrated microfluidic channels were used as additional actuators to colorize the eyes and simulate the abdominal color patterns of the peacock species by flowing colored fluids; and to induce walking-like movements in the leg structures. "This first MORPH system was fabricated in a single, monolithic process that can be performed in few days and easily iterated in design optimization efforts," said Ranzani.

"The MORPH approach could open up the field of soft robotics to researchers who are more focused on medical applications where the smaller sizes and flexibility of these robots could enable an entirely new approach to endoscopy and microsurgery," said Wyss Institute Founding Director Donald Ingber, M.D., Ph.D., who is also the Judah Folkman Professor of Vascular Biology at HMS and the Vascular Biology Program at Boston Children's Hospital, as well as Professor of Bioengineering at SEAS.

Source: Wyss Institute for Biologically Inspired Engineering at Harvard

History of Ethernet

Ethernet is the most popular and widely deployed network technology in the world. In 1973, while working on a way to link the Xerox “Alto” computer to a printer, Bob Metcalfe designed and tested the first Ethernet network. This first Ethernet network defined the physical cabling required of a connected device and defined the standard communications required on the cable.

As electronics and networking have grown, the Ethernet standard has developed to include the new technologies, but the basic mechanics of operation of every Ethernet network stems from Mr. Metcalfe’s original design at the Xerox Corporation’s Palo Alto Research Center. The original Ethernet design described communication over a single cable shared by all devices on the network.

🔺 Once a device is attached to this cable, it has the ability to communicate with any other attached device.

This allows the network to expand to accommodate new devices without requiring any modification to those devices already on the network.

In the beginning, Ethernet networks were set up in a multidrop network based on Metcalfe’s original “Ether” trunk, where devices “tapped” into the information highway. Ethernet network topologies have since evolved into star networks that include hubs, switches, and routers. A hub is a passive device that passes or buses all the information on the network to every connected device.

An Ethernet switch is a step above a hub; it incorporates the same function of a hub where it passes the data to all connected devices but includes the capability to decode parts of those messages and uses this decoded information to direct the traffic to the appropriate internet protocol (IP) address. Switches also have the ability to avoid message collisions by managing the data via store-and-forward methods that act in a deterministic fashion.

The process is prescribed in the Ethernet Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

Finally, routers are similar to switches, except they add the function of routing traffic from a LAN to another LAN, thus creating a Wide Area Network (WAN).

Maintenance Of Molded Case Circuit Breakers (MCCB)

The maintenance of circuit breakers deserves special consideration because of their importance for routine switching and for protection of other equipment.

Electric transmission system breakups and equipment destruction can occur if a circuit breaker fails to operate because of a lack of preventive maintenance.

The need for maintenance of circuit breakers is often not obvious as circuit breakers may remain idle, either open or closed, for long periods of time.

Breakers that remain idle for 6 months or more should be made to open and close several times in succession to verify proper operation and remove any accumulation of dust or foreign material on moving parts and contacts.

Frequency Of Maintenance

Moulded case circuit breakers are designed to require little or no routine maintenance throughout their normal life time. Therefore, the need for preventive maintenance will vary depending on operating conditions. As an accumulation of dust on the latch surfaces may affect the operation of the breaker, molded case circuit breakers should be exercised at least once per year.

🔺 Routine trip testing should be performed every 3 to 5 years.

Tests - Routine Maintenance Tests

Routine maintenance tests enable personnel to determine if breakers are able to perform their basic circuit protective functions. The following tests may be performed during routine maintenance and are aimed at assuring that the breakers are functionally operable.

The following tests are to be made only on breakers and equipment that are 

de-energised.

Insulation Resistance Test

A megohmmeter may be used to make tests between phases of opposite polarity and from current-carrying parts of the circuit breaker to ground. A test should also be made between the line and load terminals with the breaker in the open position. Load and line conductors should be disconnected from the breaker under insulation resistance tests to prevent test measurements from also showing resistance of the attached circuit.

Milivolt Drop Test

A millivolt drop test can disclose several abnormal conditions inside a breaker such as eroded contacts, contaminated contacts, or loose internal connections. The millivolt drop test should be made at a nominal direct-current voltage at 50 amperes or 100 amperes for large breakers, and at or below rating for smaller breakers.

The millivolt drop is compared against manufacturer’s data for the breaker being tested.

Connections Test

The connections to the circuit breaker should be inspected to determine that a good joint is present and that overheating is not occurring. If overheating is indi­ cated by discoloration or signs of arcing, the connections should be re­ moved and the connecting surfaces cleaned.

Overload tripping test

The proper action of the overload tripping components of the circuit breaker can be verified by applying 300 percent of the breaker rated continuous current to each pole. The significant part of this test is the automatic opening of the circuit breaker and not tripping times as these can be greatly affected by ambient conditions and test condi­ tions.

Mechanical operation

The mechanical operation of the breaker should be checked by turning the breaker on and off several times.

SOURCE: Electric Research And Technical Guidelines