• How many samples should be inspected?
• Where is the limit between acceptability and refusal, when it comes to defective products?

The need for an objective measurement of quality

In virtually every production batch, there will be defective products. It is true even after the manufacturer has checked each individual product and has repaired the defective ones.

Thus, in a supplier/buyer relationship, the supplier cannot be expected to deliver defect-free goods. However, the buyer wants to control the quality of purchased goods, since he does not want too many defects. But what does “too many” mean?

How to set the limit between acceptability and refusal in a way that can be agreed upon and measured?

Definition and application of ‘AQL’

The limit, as described above, is called the ‘AQL’. It stands for ‘Acceptance Quality Limit’, and is defined as the “quality level that is the worst tolerable” (ISO 2859 standard).

For example: “I want no more than 1.5% defective items in the whole order quantity” means the AQL is 1.5%.

In practice, three types of defects are distinguished. For most consumer goods, the limits are:

• 0% for critical defects (totally unacceptable: a user might get harmed, or regulations are not respected).
• 2.5% for major defects (these products would usually not be considered acceptable by the end user).
• 4.0% for minor defects (there is some departure from specifications, but most users would not mind it).

These proportions vary in function of the product and its market. Components used in building an airplane are subject to much lower AQL limits.

Getting familiar with the AQL tables

Before using the AQL tables, you should decide on three parameters:

• The ‘lot size’. If you ordered different products, the quantity of each product is a lot size, and separate inspections should be carried out for each lot. If you ordered only one product, the lot size is your total order quantity.
• The inspection level. Different inspection levels will command different number of samples to inspect. In this article, we will stick to the so-called “level II”, under “normal severity”.
• The AQL level appropriate for your market. If your customers accept very few defects, you might want to set a lower AQL for both major and minor defects.

There are basically two tables. The first one tells you which ‘code letter’ to use. Then, the code letter will give you the sample size and the maximum numbers of defects that can be accepted.

First table: sample size code letters

How to read this table? It is very easy.

If you follow my example, I assume your ‘lot size’ is comprised between 3,201pcs and 10,000pcs, and that your inspection level is ‘II’. Consequently, the code letter is “L”.

Second table: single sampling plans for level II inspection (normal severity)

sdf

How to read this table?

Your code letter is “L”, so you will have to draw 200pcs randomly from the total lot size.

Besides, I assume you have set your AQL at 2.5% for major defects and 4.0% for minor defects. Therefore, here are the limits: the products are accepted if NO MORE than 10 major defects AND NO MORE than 14 minor defects are found.

For example, if you find 15 major defects and 12 minor defects, the products are refused. If you find 3 major defects and 7 minor defects, they are accepted.

Note: in quality inspections, the number of defects is only one of the criteria. It is sometimes called “quality”, or “quality findings”. The other criteria are usually on the inspector’s checklist, which typically includes:

• Packaging conformity (barcodes, inner packing, cartons, shipping marks…).
• Product conformity (aspect, workmanship…). If all the products are in red color instead of orange, there is no need to count each sample as a defect. It makes more sense to refuse for product conformity.
• Specific tests defined in the inspection protocol (they might not be performed on all samples).

Frequently asked questions about AQL

“What are the reduced and tightened inspection severities?”

They are designed to be used in very specific situations, when a producer is particularly reliable, or on the contrary fails too often. In practice, these severities are used in less than 1% of QC inspections.

The normal severity already allows for a good variation of sample sizes. In the vast majority of cases, third-party inspectors follow only the normal severity.

“So, basically I have to authorize the factory to produce some defects?”

Yes, some defects, since a factory cannot reasonnably be expected to turn out 100% good quality.

However, it does not mean the buyer tolerates everything as long as the number of defects are below the AQL limits. Please see below the note issued in the ISO2859 standard:

“Although individual lots with quality as bad as the acceptance quality limit may be accepted with fairly high probability, the designation of an acceptance quality limit does not suggest that this is a desirable quality level. Sampling schemes [...] are designed to encourage suppliers to have process averages consistently better than the AQL.”

“Based on my AQL, I calculated the proportion of defects authorized. Why don’t they correspond to the maximum number of defects authorized?”

It is true. In our example above, 2.5% of 200 samples is 5 samples, but we accept the goods even if 10 samples are found with a major defect.

Why this difference? There are heavy statistics behind this issue. To make it simple, the producer runs a risk of rejection (based on the random element when drawing the sample) even though his products (if they were all checked) would be accepted. And, in the same logic, the consumer runs a risk of accepting bad products. The statisticians had to account for these risks, that’s why the numbers were adjusted and seem not to make sense.

“Why not just say, ‘we’ll check 10% of the quantity’, or whatever percentage deemed appropriate?”

Here again, the statisticians tell us it is not that simple. As we go up in the total quantity, the proportion of products checked can decrease, for the same confidence in the inspection results.

As you can see in the chart below, the number of samples to check (vertical axis) increases at a slower pace than the total quantity (horizontal axis).

Replacing Halogen Spotlight Bulbs with LEDs
During the last 10-15 years, halogen spotlights have become more and more popular in British homes. Halogen bulbs (pictured above) are typically available in low voltage 6V or 12V (supplied with adapter) and high voltage 240V versions with 20-50 Watt power ratings.

Replacement 12V LED spotlights are now available and becoming more and more economical to purchase. Dichroic Halogen bulbs start at around £1 each and last for 2,000 hours – LED spotlights are priced as low as £4 each and will last 80,000 to 100,000 hours! The total power consumption for an LED spotlight is an ultra-low 1-2 Watt for a bulb offering similar light levels to a power hungry halogen bulb.

LED Spotlight Options

LED Spotlights are available in a range of optical beam angles from 6 to 25 degrees, so you can choose how intense a spotlight you require – narrow beam for a dedicated reading light, wide beam for more diffuse mood lighting. They come in industry standard fittings: MR16, and GU10 so you can very simply replace all the spotlight bulbs in your home and start saving on your electricity bill each month.

Buy LED Spotlights

Currently, one of the cheapest places to purchase LED spotlights is eBay. A huge range of different colours and light intensities are available from as little as £3.50 including postage. Click here to search eBay now for MR16 LED (12 VDC or 12 VAC), and here for GU10 LED (mains powered 110/240 VAC).

NEW 12V LED spotlights (pictured at the top of this article) and MR16 ceramic bulb holders are now available from the REUK Shop.

NEW Pure brilliant white 240 Volt LED spotlight bulbs (pictured above) are also available in the REUK Shop. These 1 Watt rated bulbs with GU10 fitting can be used as a direct replacement for 240 Volt halogen spotlights (except in dimmer circuits)

In situations where these low-voltage and mains-voltage LED spotlights are not always bright enough (e.g. for general room lighting), consider Cree LED spotlights which are spotlights made up of one or more 1+ Watt LED bulbs, or Megaman dimmerable CFL spotlight bulbs.

12V LED Spotlights and Renewable Energy
12 Volt LED Spotlights are being used more and more in off-grid renewable energy situations where an array of solar panels, or a wind turbine, is charging a 12 volt battery bank with power. Using 12 volt appliances, devices, and lighting costs a little more up front, but there are no energy losses caused by having to step up voltage to 240V AC using an inefficient power inverter if you use 12 volts throughout. A typical power inverter burns up around 50 Watts of power just converting DC from the batteries to AC – enough power to light fifty 12 volt LED spotlights.
nb. This only works well if the battery bank is close to the site where you intend to use the stored power or there are voltage losses over the cables.

Click here to read about how to set up Shed and Garage Solar Lighting with 12V LED spotlights.

commont:
I have been trying various combinations of batteries,12 volt bulbs, low energy lamps, LED lamps and LED strips over the past couple of years now.
The normal 12 volt lights found in caravans and the like are OK, but they do drain the battery quite quickly. Low energy lamps take a while to warm up, they are not as bright, but do use less power thus extending the time between charges for the battery.

By far and away the best are the new LED products coming along. We now have 12 volt LED strips as down lighting under the wall units in the kitchen, we have just fitted two LED candle bulbs in the cooker hood, a 12 volt LED table lamp and a 220 volt LED standard lamp (Bought by mistake – I thought it was a 12 volt!) in the lounge and more LED strips illuminating the stairs and hallways. These come to full power instantly and use so little power we can leave them on all evening without any thoughts to the consumption.

The LED bulbs come in a variety of fittings and have mains as well as 12 volt.

Comparing the prices to your earlier articles show just how much they have come down and the range available today.

Lozol

2012 is coming, what will happen about LED?

Let’s find some way forward.

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3 C authentication is actually English name “China Compulsory Certification” (China Compulsory product Certification system) English abbreviations, it is also the national Compulsory product Certification use of the unity of the sign. It is the Chinese government according to the wto agreements and the international prevailing rules, to protect the consumers’ personal and animal life safety, protect the environment, to protect national security, the implementation of laws and regulations in accordance with a product conformity assessment system. Its main characteristic is: national publication unified directory, determine the applicable national unity standard and technical rules and implementation procedures and work out unified marks logo, the provisions of the uniform charging standards. That falls within the compulsory product certification directory of the products must be specified by the state certification institution to the authentication and has been qualified relevant certificates and put the authentication marks, can leave the factory, import, sales and service site use in business. At present, China announced the first batch of authentication products must pass mandatory there were 19 categories of one hundred and thirty-two. Mainly includes the wires and cables, low voltage electric appliance, information technology equipment, safety glass, fire-fighting products, motor vehicle tyre, latex products, etc.

XTZ

Germany VDE is national product marks. VDE test institutions and the authentication association is German electrical engineers association of the subsidiary body, it was established in 1920, as an international recognized electronic appliances and parts safety test and claiming compensation organization, in European and international have enjoyed a high popularity. At present the customers all over the world to the needs of the VDE authentication in the rising trend. VDE test institutions and the authentication association European and international standard according to the current, each year about for 2200 a German customers and about 2700 foreign customers 18000 times of the test. Today, the world has more than 200000 kinds of products have VDE safety certificate.
VDE’s full name is the Prufstelle Testing and Certification Institute, which means that the German electrical engineer association. Founded in 1920, is the most testing experience of Europe test and inspection agencies authentication, one of the European Union is authorized CE announcement institutions and international CB organization members. In the European and international, get the electric products CENELEC European certification system and CECC electronic components quality evaluation of the European coordination system, global IEC electrical products, electronic components such as recognition of authentication system. The product is very extensive evaluation including household and business use of electric equipment, IT equipment, industrial and medical science and technology equipment, assembly materials and electronic components, wire and cable, etc.

CE certification

“CE” mark is a kind of security authentication marks, is considered as the manufacturer and opens to enter the European market pa

(1) Should be used in the DC power supply
Some manufacturers in order to reduce the cost of product use “resistance and capacitance buck” way to LED products supply, it will directly affect the life of LED products. Using special switching power supply (had better be constant current source) to LED products power supply will not affect service life of the product, but the product cost relatively high.

(2) Need to be done to prevent electrostatic measures
LED products in the process of production to by a certain anti-static measures, such as work tables to grounding, workers wear anti-static clothing, take anti-static ring, and with antistatic gloves, conditional can be installed anti-static ion fan, also want to ensure workshop humidity at around 65%, in order to avoid air too dry produce static, especially green LED relatively more easily to be electrostatic damage. In addition, different quality grades of antistatic ability LED is different also, quality high class LED antistatic ability is ambitious some.

Here again detailed introduction of electrostatic knowledge: the essence of the static electricity there are remaining charge. Charge is all the relevant electrostatic phenomenon in nature of the physical quantities, called in English
ESD. Potential, electric field, the current, the amount of relevant because of the existence of charge of the charge or as a result of the mobile physical quantities. A lot of electrostatic problem was because people don’t have ESD consciousness, and by even now also many people doubted ESD will damage of electronic products. This is because most ESD damage occurred in the sensation of the following, because the human body to electrostatic discharge perception about 3 KV voltage, and many electronic components in hundreds of v even a few volts will damage, usually electronic device are ESD damage has no obvious after line, the elements in PCB again after the installation of testing, the results appeared a lot of problems, analysis is difficult. Especially the potential damage, which USES precision instrument is also hard to measure the performance have apparent change, so it was all electronic engineers and designers are all doubt ESD, in recent years, but the experiment proves, the potential damage in some time later, the reliability of electronic products to decline significantly.

(3) LED temperature:
To pay attention to higher temperatures will make LED resistance smaller when the outside environment temperature, LED light source resistance will be reduced, if use voltage power supply can cause LED working current increases, when over the rated current, affect the service life of LED products, serious will make LED light source “burn out”, so had better choose the constant current source power supply, to ensure the working current LED by the influence of the temperature of the outside world. LED temperature is also affect the service life of the LED the most important factor. Please take seriously.

(4) LED products sealing
No matter what LED products, as long as used in outdoor, are faced with waterproof, moistureproof sealing problem, if processes is not good will directly affect the service life of LED products. Now have a few on the product quality demand is higher in the manufacturer of the use of the traditional epoxy resin “on” way to seal LED products, this kind of method operate up more troublesome, for large LED products is not very suitable for, also can cause the weight of the product increase.

(5) LED the current can’t more than a LED IF current: over current work will make LED life drop very quickly, IF exceeded come, will soon LED to burn out.

(6) The welding temperature: T welding temperature in T260 ℃ T or so, time control in T5ST less than, welding points away from the bottom in the T2.5 mmT above gel, DianLaoTie must be grounded. Absolutely not, however, give charged welding LED.

1, auto part: installed inside the car use dashboard, speakers, including indicator light, and automobile external (the third the brake lights, or so tail light, direction of the light, etc), the Europe type series including audi, BMW, fox, all is the brand listed high brightness LED, and depot, Toyota will also take the lead in the instrument panel back panels with high brightness LED, other each depot new car, also in succession in use. If plus the lamp, before and after the brake lights, traffic signs and so on, with traffic relevant market, the opportunity is very large. In the traffic signal lights market, global about 20 million a traffic signal lights, if is updated every year 2 million seats, business opportunities can be extended for 10 years.

2, back light part: T mobile phone is mainly in the back light light source, is the biggest application type SMD products market. Although the rate of growth of mobile phones in the past two years has been far more gradual, but there are still 400 million cigarettes level throughout the year, with 1 cell phones to LED back light 2 star, buttons and a SMD LED plan, a year conservative 400 million cell phones demand LED about 3.2 billion star. South Korea blue backlighting recently mobile phone agitation, make the market demand blu-ray LED, it shows the mobile phone in LED application the market still holds the balance of power. Following the blu-ray to phones, the market is the mobile phone has labeled. Previous cell phone is a high-end products labeled, but this year the main component prices, making cell phones and mobile phone monochromatic color of the split between narrowed, and manufacturers to promotion of, the mobile phone HuanXing tide quietly happen.

3, screen: T the LED display as a new show media, along with large scale integrated circuit and the rapid development of computer technology, obtained the rapid development, it with the traditional show media-and colorful neon lights, pixel tube TV wall, four color magnetic flap, in comparison with its high brightness, the dynamic image display effect, low trouble, less energy consumption, long service life, display content diversity, showing the way the rich, high ratio of performance advantages, has been widely used in many fields.

4, electronic equipment and lighting: T LED to its low power consumption, small volume, long life characteristics, has become the first choice of various kinds of electronic equipment indicator, now almost all of the electronic equipment have LED figure.

5: special work lighting and military use: T due to the extent, weather has LED light source, good sealing, and low thermal radiation, small volume, easy to carry, etc. It can be used in explosion-proof and field operations, mining, military action and other special workplace or bad work surroundings.

6: decoration: T can be widely applied in the shine stereoscopic word; Landscape architecture appearance lights; Elevated, tall buildings, roads, Bridges, landmarks, building signs hair light source; Advertising stereo word, mark, mark, and shew light source; Commercial space, airport, construction engineering, subway, hospital, hotel, BaiHuo stores, square, restaurants, PUB lighting design; Automobile, transportation, ships, publicity instructions warning light source; Computers, mobile phones, communication, mouse, signal transmission application with the light source LED the development of technology, the LED lighting products is the development as a direction, is also a necessary direction, the use of LED will only more and more widely, friends may also to create the new field application LED.