They’re in their early 20’s, freshly out in the world and earning good money, driving flashy cars that are absolutely dripping with expensive extras. Who are they?

They’re the latest “in crowd” women. They are demonstrating their freedom, independence and individuality and are apparently earning the money to fund their ladette lifestyle. Their souped-up cars with their throaty sounding wide exhausts, fancy spoilers and alloy wheels can be heard approaching from a distance by the drumming of the full-on car stereo. Quite clearly they intend to stand out from the crowd and the crowd can hardly ignore them. Figures released recently tell us that 18 per cent of women drivers in the 21 to 25 age group are driving these cars with their costly modifications and specialist trims, normally associated with male drivers.

The resulting increase in car insurance premiums in this group of drivers is hardly surprising. Their cars with their flashy modifications and expensive extras certainly attract attention and in all probability it’s not the sort of attention their drivers would choose to seek. Thieves are attracted to these flashy and expensive cars. The extras alone are tempting and easily re-sold on the second hand car accessory market.

Car insurance in general is falling and this is true for women in particular. Women generally have fewer accidents, do less annual mileage and are considered less aggressive drivers than their male counterparts.

Because of these statistics, insurers are very happy to insure female drivers. There are companies specializing in this market and there has been a great deal of advertising in the press and on television. All these companies are vying for business and have their own specific niche markets. There are carefree girlie groups, very posh middle aged women and young mums featured in the ads. These specialist insurers can’t be relied on to offer the best deals, though, not matter how attractive the ads or catchy the tunes. In all probability you’d find a much better quotation for your insurance by going to one of the internet brokers who’d come up with comparative quotes for you. You need to compare the cover, of course, but they’ll check out all that for you too, and even offer an on-line discount in the bargain.

Should the trend for flash and extras extend across the market, then certainly insurance premiums would show a marked increase, making it doubly important to shop around.

Incidentally, it’s the loyal customers who tend to get left behind in the best premium stakes. It’s very easy to get into the pattern of sticking the renewal notice behind the clock until more or less the day the policy is due to be renewed and then a quick call to the insurer and your insurance money is committed for another year. Spend a little time (and it really is very little) to find an on-line broker who’ll come up with some choices for you. If the price isn’t beaten, there’s nothing lost and you can remain loyal to your insurer. All the information the broker will need will be there on your renewal notice.

It’s worth the trouble. Honestly.

Michael Challiner
http://www.articlesbase.com/advice-articles/car-insurance-freedom-independence-52697.html

In today’s advanced world of technology, the Internet has made it possible for us to shop for almost everything online. Car insurance is no exception, and drivers in California are able to purchase car insurance from the same auto insurance company used by drivers in West Virginia thanks to the Internet and the broad scope of advertising it provides.

However, when you are looking for cheap Texas car insurance, you should not overlook the option of purchasing the insurance from a Texas car insurance company. Purchasing cheap Texas car insurance from a Texas car insurance company does not mean purchasing the insurance from a company that is merely licensed to do insurance business in Texas. A Texas car insurance company is one that specializes in selling car insurance to Texas drivers and car owners.

Texas-based car insurance companies are able to sell cheap Texas car insurance because they are aware of any special factors that should go into car insurance in Texas. Rather than simply having policyholders in Texas, they have owners and agents in the area.

A Texas car insurance company will ask Texas drivers and car owners the same kinds of questions asked by any other car insurance company. The insurance company will want to know contact information about you, such as your name, your address, your telephone number, and your email address, as well as more personal information such as your marital status, gender, age, employment, and credit rating. The insurance company will also want to know information about your current Texas car insurance, information about your vehicle such as make, model, year, and vehicle identification number (VIN), and information about the people who also drive your car.

To begin your search for cheap Texas car insurance, start at home. Look at your newspapers, local television commercials, and telephone listings, and talk with your family members, friends, and co-workers about the Texas car insurance companies they use.

Elizabeth Newberry
http://www.articlesbase.com/finance-articles/cheap-texas-car-insurance-98888.html

For the private owner to market a car for sale while avoiding the risks associated with selling it privately is no small undertaking. The following points should be considered:

Secret #1: Evaluating Personal Circumstances

The kind of person you are and the circumstances you’re in play a key role in the decision to sell your own car. Before setting out to sell your car yourself, make sure that you have confidence in negotiating with prospective buyers. Test-drives and phone calls are part of the process, so it’s vital to be prepared to handle these as well. Simply knowing yourself and what you’re going to face is absolutely critical.

Secret #2: Being Armed With Knowledge of the Market

The best way to begin when first planning to sell a car privately is to know the market–to be armed with enough information. This ca be done by simply determining how much the old car is worth. Try to determine the answers to these important questions: Is the car going to be easy to sell? Is it a popular commodity? Is it likely to receive multiple offers? What kind of buyer is most likely to be interested in this kind of car? In order to answer these problems with accurate results, the first step should be to check some car ads online.

Several online used car guides are now available on the Internet. By knowing a car’s make, model, mileage, and general condition these Web sites will doubtless prove to be a good place to begin determining the value of the vehicle. Based on those basic details it is quick and easy to secure accurate estimates for things such as how much a local dealer is likely to offer for it as a trade in. It is also helpful for determining how much to expect to make by selling your car privately by visiting and examining the used car guides on the Web.

The used car price guides that are now commonly available at libraries or bookstores are useful in addition to checking the online used car guides. The local newspaper’s automotive advertising section can also be checked for similar vehicles. By combining information from all of these sources it will become easy to gain the knowledge needed to be fully prepared for private automobile sales.

Robert Williams
http://www.articlesbase.com/automotive-articles/selling-a-car-96574.html

With the popularity of the recent Disney Pixar Cars movie, chances are that your little boy is wanting Lightning McQueen, Mater, and all their friends to now grace any surface of his bedroom. Decorating a room with a Disney Cars room dcor is fairly easy and inexpensive. Merchandise is available all over the web and if you are lucky, you may moreover afford an item or two in the stores. Because of the popularity of the movie, all Cars merchandise has continued extremely popular so I undergo learned that when you find an item you want that isn’t sold out, you have to move quickly and buy it.

So what is available for decorating a Disney Cars theme room? Well first, you will suffer you selection of a couple of beds. A Disney Cars toddler bed is available as is a Lightning McQueen Race Car bed that comes in a twin size. You will too be able to find Disney Cars toddler bedding and twin size bedding sets.

It doesn’t stop with merely beds and bedding though. The duration of Disney Cars room dcor available extends to wall art, room decals, lamps featuring Lightning and Mater, and much dresser knobs featuring many of the movie?s key characters. You will furthermore be able to find Disney Cars furniture pieces including toy boxes and table and chair sets for your Disney Cars theme room.

So if your little boy has carried on dreaming of a Disney Cars themed bedroom, you will own no trouble coming up with enough Disney Cars room dcor to create the Lightning McQueen room of his dreams!

virgilio vallecera
http://www.articlesbase.com/cars-articles/decorating-a-room-with-disney-cars-room-decor-750501.html

From the clothes we wear and the way we decorate our homes to the type of music we listen to, many aspects of our lives demonstrate our own tastes and personalities. More and more motorists are choosing to carry on this trend onto their otherwise standard vehicles by finding personal registration plates for their cars. In their simplest form a British car registration is used to identify vehicles on our roads. However in a more exciting and popular light, a car registration can personalize our vehicles and enable us to make our individual mark on our cars. Over 3500 new car registrations are sold each week in the UK and this number continues to rise.

Since the introduction of the internet, finding personal car registration plates for British vehicle owners is incredibly easy. With an average of 30 millions car registrations available at any one time, number plate dealers provide easy to navigate websites to narrow down your search as quickly as possible. Vehicle registration numbers are available in many formats including dateless number plates, suffix and prefix car registrations and the new style of British car registrations that the DVLA currently issue.

When finding car registration plates there are countless personal ideas to search for. Many personal car registration numbers on todays roads read peoples names or initials. Name plates account for some of the most expensive number plates on the market and many are worth several thousand pounds. Thankfully cheaper alternatives are available and the majority of people who are finding personal car registrations opt for a car registration plate with their initials. This difference in price occurs because there are many combinations of initials available however with name plates there is just one perfect combination. Thousands of car registration numbers are now available for under 300.

Other popular searches when finding personal car registration plates are numbers relating to a date of birth or lucky and sacred numbers such as 7, 888 and 786. Many businesses also purchase vehicle registration for fleet cars and delivery vans to attract attention on the roads with a piece of unique advertising. Business car registration plates could read the company name, managers initials or words relating to their industry. Pimlico Plumbers in London are no strangers to this with their highly amusing and valuable collection of plumbing related car registration numbers. They own vehicle registrations such as LAV 1, BOG 1, W4 TER and DRA 1N amongst many others, all of which are assigned to their fleet of work vans.

Once you have found your new car registrations you can assign them to your vehicle at your local DVLA office or by posting your application to DVLA Swansea. You will need to include your V5 logbook and MOT certificate if applicable and in return you will receive a new tax disc displaying the new car registration and an update V5 logbook will follow a couple of weeks later. The new tax disc will have the same amount of license period left on it. Once assigned to a vehicle there are no other costs involved and British car registrations do not affect car insurance premiums.

Alternatively new car registrations can be kept on certificate for up to 12 months and then renewed annually for 25 payable to the DVLA. This feature allows people who are finding personal car registration plates to buy them even if they do not have a vehicle to assign the new car registration to.

Ross O’donnell
http://www.articlesbase.com/automotive-articles/finding-personal-car-registration-plates-for-british-vehicle-owners-122647.html

Introduction to PLC’s

Programmable Logic Controllers

Bedford Associates, founded by Richard Morley introduced the first Programmable Logic Controller in 1968. This PLC was known as the Modular Digital Controller from which the MODICON company derived its name. The History of the PLC as told to Howard Hendricks by Dick Morley provides an interesting insight into the early development of the PLC.

Schnieder Quantum PLC

Programmable Logic Controllers were developed to provide a replacement for large relay based control panels. These systems were inflexible requiring major rewiring or replacement whenever the control sequence was to be changed.

The development of the micro processor from the mid 1970’s have allowed Programmable Logic Controllers to take on more complex tasks and larger functions as the speed of the processor increased.

Ladder Logic

PLC had to be maintainable by technicians and electrical personnel. To support this the programming language of Ladder Logic was developed. Ladder Logic is based on the relay and contact symbols technicians were used to through wiring diagrams of electrical control panels.

Until recently there has been no formal programming standard for PLC’s. The introduction of the IEC 61131 Standard in 1998 provides a more formal approach to coding. PLC Manufacturers have so far been slow on the uptake of the standard with partial implementation. The SearchEng articleIEC 61131-3, a Standard for PLC Software by R.W. Lewis provides an introduction to the standard.

The documentation for early PLC Programs was either non existent or very poor, just providing simple addressing and basic comments, making large programs difficult to follow. This has been greatly improved with the development of PLC Programming Packages.

SCADA and HMI

The early programmable logic controllers interfaced with the operator in much the same way as the relay control panel, via push-buttons and switches for control and lamps for indication.

The introduction of the Personal Computer (PC) in the 1980’s allowed for the development of a computer based interface to the operator, these where initially via simple Supervisory Control and Data Acquisition (SCADA) systems and more recently via Dedicated Operator Control Panels, known as Human Machine Interfaces (HMI).

The History of the PLC
as told to Howard Hendricks by Dick Morley

The following are some fables associated with the first ten years of the programmable controller business. These Fables may or may not have a basis of truth, but in general, they are the best that my Alzheimer-plagued memory can do at the moment. As has been often in other articles and reports, the startup of Modicon and the programmable controller industry as a whole is well documented. The programmable controller was detailed on New Year’s Day, 1968, and from hence till now, a slow steady growth has allowed the manufacturing and process control industries to take advantage of applications-oriented software.

The early days however, were not as straightforward nor as simple. We had some real problems in the early days of convincing people that a box of software, albeit cased in cast iron, could do the same thing as 50 feet of cabinets, associated relays and wiring. The process was indeed difficult, and deserves some of the stories that I hope the reader will be regaled with as he proceeds onward through the tortuous swamp of my mind.

One of my earliest recommendations was that the programmable controller, according to my own system architecture specification, did not need to go fast because I felt as though speed was not a criteria because it would go as fast as we needed it to. The initial machine, which was never delivered, only had 125 words of memory, and speed was not a criteria as mentioned earlier. You can imagine what happened! First, we immediately ran out of memory, and second, the machine was much too slow to perform any function anywhere near the relay response time. Relay response times exist on the order of 1/60th of a second, and the topology formed by many cabinets full of relays transformed to code is significantly more than 125 words. We expanded the memory to 1K and thence to 4K. At 4K, it stood the test of time for quite a while. Initially, marketing and memory sizes were sold in 1K, 2K, 3K, (?) and 4K. the 3K was obviously the 4K version with constrained address so that field expansion to 4K could easily be done.

The question of speed, in part, was part of the early designs. No interrupts were necessary because the external signal conditions were directly written onto memory without any supervisory requirements or “operating system of the conventional type. This allowed the processor to pay attention to solving logic rather than housekeeping the I/O. As a result, of course, the processor had to have significantly more processing power than normally associated with this size computer; and secondly, the system had to be made to run fast.

We increased the memory size, as mentioned above, but to get it to run fast, we had to break up the machine into three distinct components. Initially, the programmable controller was conceived of a processor board and a memory, and that the algorithmic and logical manipulation would be done in software. This approach was painfully slow, both on the generic “store bought computers, and other items.

We did, however, manage to substantially speed up the machine by making a third major component. This was called the logic solver. A logic solver board solved the dominant algorithms associated with solving ladder logic without the intervention and classical software approach of general-purpose processing. This meant that we ended up with three boards; memory, logic solver and processor. This single step allowed us to get the speed we needed in this application-specific computer to solve the perceptually simple problem of several cabinets full of relay wiring.

We had also assumed a modular approach to the programmable controller. In act, the name Modicon means MOdular DIgital CONtroller. The modularity, however, was soon abandoned because, as everyone knows, open architectures are no good. We instead had the marketing premise that a large footprint would contain within it the sets of problems we wished to solve. This meant that a buyer of programmable controllers could buy large numbers of the same units, and the software and hardware would be identical across a broad spectrum of applications in his factory. Service, maintenance and total life cost would be substantially lower than the perceived lower cost of an open architecture and modular expansion. Although at first, a supporter of the open architecture modular expansion, I soon became convinced by the marketplace, but this was folly.

We took one of our early units which was aimed at the machine tool industry because of my Bedford Associates consulting background, up to one of the early requesters of this equipment. This particular early requester was Byrant Chuck and Grinder in Springfield, Vermont. We took the machine up there, and it was heavy. This was the 084. The 084 was in the trunk of my old Pontiac, and since we needed help carrying it in, requested some of the people at Bryant to help us. We went out and opened the hood, and the first comment made by an outside viewer of the programmable controller said, “Thank God it,s not another pastel colored piece of sheet metal.

We can hypothesize from this particular comment that the ruggedness of the visual design was pleasing to him, and being human (as opposed to Martian), assumed that this same attitude went deep inside the construction of the machine in both the hardware and software. Indeed, this was the case, and the machine as a result, was built rugged, had no ON/OFF switch, had no fans, did not make any noise and had no wear out system.

To reminisce for a moment—in selecting the cores for the first memories, which in itself was a revolutionary step, we selected these cores and we applied Shannon,s Law. Shannon,s Law assumes that the signal-to-noise ratio is what makes signals good or bad. There are several ways to get the power from the signal-to-noise ratio; one is to code heavily, be triply redundant, and use lots and lots of error checking. There is another way, which is perfectly compatible with theory, which is to use lots of signal power in another domain. A nice switch, a car battery and a D-rated light bulb will work fairly well over a long time period.

Therefore, what we did was rather than going error checking, triply redundant and stuff, we got, and searched for and found high energy, large ferrite core memories that had lots on energy per bit. We still make the same assumption today. The energy per bit is extremely important—as Shannon,s theory said in his most famous 1948 paper, that the signal noise to power noise is what gives you transmission. the way we got signal power was to increase the energy per bit. This we felt was far more important than getting the energy per bit increased by means of doubly transmitting it. But I digress. Bryant Chuck and Grinder put it in, and liked the equipment so much that they never bought one. They in turn thought it was a good idea, and as many did at that time, tried to evolve their own.

One of our first major customers, however, was Landis in Landis, PA. We flew the equipment down in a private aircraft, and with apprehension because we were late (as usual), brought the equipment into Landis. In doing so, we tripped over the threshold. The equipment went KA-RASH onto the floor! Without much chagrin, we picked the equipment up, trundled it in. hooked it up, and low and behold, it worked quite well.

Now, Landis was pleased and surprised. They were pleased because it worked, but they were most pleasantly surprised—not because the equipment worked—but because the guys from Modicon fully expected the equipment to work in spite of it being dropped. In other words, the people from Modicon weren,t nervous about the fact that it fell on the floor over the threshold.

Landis subsequently took and wrapped welding coils of wire around the machine to induce electro-magnetic noise to see if they could make it fail. We had them there! We used to test the programmable controllers with a Teslar coil that struck a quarter inch to half-inch arch anywhere on the system, and the programmable controller still had to continue to run. There was significant strangeness with respect to the programmable controller. For example, it had no ON/OFF switch. It had no means to load software. It had no fans. It ran cool. It could survive bad, physical and thermal environments. It was not computer industry standard. There were many things that were most difficult in the acceptance of the programmable controller, and early acceptance was most difficult indeed.

Our sales in the first four years were abysmal. Early innovators such as Landers and General Motors were, of course, heroes to our eyes, but they would buy small numbers of units and then test them in the field before they committed themselves later on. We had one customer in the utilities business that took them approximately six to seven years to make a decision to but the first one.

We never really sold any programmable controllers into the intended market which was machine tool control such as lathes, grinders and stuff, but we did, as luck would have it, stumble across the transfer line market which was and still is the mainstay, long-term market for the application of programmable controllers. Discreet parts manufacturing in an automatic environment, i.e., mass production, continues to be, and probably will be for the future, the mainstay of the programmable controller industry.

Some of the more interesting stories center around the personalities and experiences as opposed to the programmable controller. Modicon,s third president (or fourth, if you count my two-week stint) was Don Kramer. When Don Kramer was chosen as president, we decided to go out and celebrate at the Lanum Club in Andover. At the time, we felt we should celebrate over both martinis and food. As we were leaving the shop for the Lanum Club, Don made the aside comment that “the place is dingy and needs a paint job. As we were leaving, I mentioned to Don that as president you have to change what you say, and not be very open—you have to be a little careful about what you say because employees, customers, and boards of directors tend to take what you say as truth. Rather than listen to the meaning, they listen to the literal statements, and one must be careful. We went over to the Lanum Club and had a nice glowing two hours of discussion, food, and drink. Coming back, as we entered the Modicon lobby, we noticed that there was scaffolding about and people were painting. We went over and asked Lou as to why these people are painting since, at the time, we don,t have any money. Who ordered this paint job? And Lou looked Don Kramer straight in the eye, and said, “Why you did, Mr. Kramer. Nuff said.

As has been mentioned many times, your author, that,s me—Dick Morley—is supposed to be the inventor of the programmable controller. This is at best, partially true. The thing that made the Modicon company and the programmable controller really take off was not the 084, but the 184. The 184 was done in design cycle by Michael Greenberg, one of the best engineers I have ever met. He, and Lee Rousseau, president and marketeer, came up with a specification and a design that revolutionized the automation business. they built the 184 over the objections of yours truly. I was a purist and felt that all those bells and whistles and stuff weren,t “pure, and somehow they were contaminating my “glorious design, Dead wrong again, Morley! they were specifically right on! the 184 was a walloping success, and it—not the 084, not the invention of the programmable controller—but a product designed to meet the needs of the marketplace and the customer, called the 184, took off and made Modicon and the programmable controller the company and industry it is today. My compliments to the two chefs—Lee Rousseau and Mike Greenberg.

The issue of quality in programmable controllers is a story that is normally taken for granted. The gentle reader must remember that our engineering people came from the computer industry where reliability in those days was a phantom—a phantom of design, a phantom of cost. People felt that reliability was something other people did, and that if we only could deliver faster computers, even if they didn,t work, everything would be fine.

When the programmable controller was designed, it was designed in to be reliable. We used lots of energy per information bit by utilizing D-rated components, large memory ferrite cores, relatively stable and large etchings on printed circuit boards, totally enclosed systems and conductive cooling. No fans were used, and outside air was not allowed to enter the system for fear of contamination and corrosion. Mentally, we had imagined the programmable controller being underneath a truck, in the open, and being driven around—driven around in Texas, driven around in Alaska. Under those circumstances, we anted it to survive. The other requirement was that it stood on a pole helping run an utility or a microwave station which was not climate controlled, and not serviced at all. Under those circumstances, would it work for the years that it was intended to be? Could it be walled in? Could it be bolted in a system that was expected to last 20 years?

The humorous side of this is though we did all those designs and very carefully tried to make this system as intrinsically reliable as we could, not by redundancy, but by building well. In other words, it was designed to be built, it was designed to be designed, and it was designed to be reliable. We, however, as engineers, didn,t understand the accountants and manufacturing. those two have their grail, shipments by the end of the month. As far as we could ascertain at the time, shipments were made independent of quality and independent of whether or not the system ran.

In the early days of the programmable controller and Modicon, even though I wasn,t a direct employee and an owner, I would give out my home phone number to many of our critical customers so that if they had a problem, they could call me directly. Several calls indicated that when we shipped near the end of the month, let’s say October 34th, that the equipment would not run; and secondly, when they opened the box and took the machine apart, cards were missing, bolts were on the bottom of the cabinetry, and some of the cards were not fully inserted. In other words, to make the end of the month was much more important than to deliver equipment that ran. to put it mildly, we were pissed! How do we as engineers maintain quality without continual surveillance which is most difficult for the design and entrepreneurial mind set. What we did was specify and design “blue boxes. These were cabinetries that the system had to operate in and run continuously for a minimum of 24 hours, under load, and under varying conditions. The box was built out of plywood, but its primary intention was to heat cycle the programmable controller under various input/output loads. We also ran, as a specification, that a Tesla coil was to be used on the programmable controller, and that vibration and thumping with a hammer (rubber) would be part of the specification.

This may seem unscientific to many of you, but let us assume that you try to get your equipment to run while somebody purposely tries to destroy it with a rubber hammer or spark coil that he can put anywhere on the system. Remember, your intention is to make the processor stop. That combination significantly depressed those monthly shipments during the first period. As a result of that, however, the message got through. Not only did we build ovens and tests, and pay attention to heat and spark and RF emissions, we would run the system continuously even in the shipping crate to get the maximum number of pre-custom hours we could. It was important to us that we found the mistakes and not the customer and his secondary customer.

The language itself, ladder lister, bears some discussion. This particular language was not the invention of Modicon. We hypothesize that the language is very old, and originated in Germany to describe relay circuitry. If one looks at ladder lister, it has been our technical community for so long, we somehow think those little symboligies actually look like relays. In fact, it,s a mnemonic form of rule-based language, very modern and very high level, but designed in a Darwinian fashion over a period of many decades.

The ladder logic construct, “If… Then… is a very powerful construct used today in expert systems and other rule-based languages. The symbology, allowing normally open and normally closed situations as well as parallel and serial representation, was used for many decades before the invention of the programmable controller. I have worked on machines where the number of C-size and D-size prints were hung in special racks, and would be up to three feet thick worth of documentation on those drawing sets.

The name ladder comes from the fact that on the right-hand of the drawing is one power rail and the left-hand side is the other power rail; and in between in a horizontal fashion, is the statement or sequential connection of logical elements which we call relays or relay logic. The initial 084 had only logic in its functionality, and as a result, was marginal. In other words, all we did was replace relays rather than enhance the functionality by a factor of ten which is the entrepreneurial rule. Immediately, of course, based on customer response and our own frustrations, we put thing in the ladder listing language such as addition, multiplication, subtraction, and other functionalities that went far beyond relay capability and entered the realm of mathematics and set theory. This was still not sufficient, however, and we needed some way to make a “call to a “subroutine using ladder lister symbology and representation.

A software engineer, Chuck Schelberg, and myself were in the conference room one day trying to ascertain how we could make a generic call to functionalities that far exceeded the relay symbology and representation, and came up with the “DX function. This function was a block function that would be an element on the ladder logic representation that could perform many functionalities including arrays, motor drive functions, servo functions, extended mathematical functions, PID loops, ad nauseam. We felt there would be an occasional representation and use of these functionalities, and that not much had to be done to the programmable controller other than to modify the software. Wrong again!

The first customer that took delivery of a programmable controller utilizing the DX function, had a capability to be predictable and operate in real time. The RUN light went out, and the time to execute a scan or complete transformation of the ladder logic went far beyond the time allowable. Every single line had a DX function on it. Again we learned that when you enhance functionality, people use it all. I have never designed a computer that had too much memory. I,ve only designed computers that have too little memory. The same thing applies to any other functionality. Conventional wisdom seems to think that price/performance depends on only one thing—price—when, in fact, my experience has been that the customer cares little about price.

This price/performance tirade being over, one of the lessons we learned is that the customer wants functionality over the entire life cycle cost installation of the job. the customer also wants ease of installation, to have some fun, and to be proud of the work he does. After he,s finished, he never wants to come back.. The equipment should work as installed and as based. At one time, the programmable controller meantime before failure in the field was 50,000 hours. This is far in excess of almost any other type of electronic or control equipment.

The concept of languages and high-level languages is important. The programmable controller, as it evolved, began to request more and more power, and more and more memory. The memories continually went up as well as power. It is estimated that at one time, in the mid-1970s, that the programmable controller had the equivalent of two MIPS processor and 128 kilobytes of memory, which at that time was a significantly powered minicomputer capability. Why? High-level languages require power to run them. If we take the equivalent of the ladder lister statement “If… Then…, the high-level language as represented here, requires a substantial amount of interpretive compiler, if you will, generation of underlying code. In other words, this statement spawns significant underlying code that must be run quickly, reliably, and contain within it, all aspects of resource allocation and operations resource. The higher level the language, the more powerful the processor apparently has to be in order to run the language. Ladder lister is a high-level rule-based language which, until now, we haven,t talked much about in these terms. Our customers treated the programmable controller as a box of relays, and well they should. Language theory is neither necessary not desirable for most of the customers to know. The customers, instead, understand their problem, and are indeed much smarter than the design engineers because the dimensions of their problem far exceed the relatively simple problem of designing a computer software system and language. Ladder lister requires high performance which is one of the reasons it has difficulty running on the personal computer even of today

INTRODUCTION TO SCADA

SCADA is the abbreviation for Supervisory Control And Data Acquisition. It generally refers to an industrial control system: a computer system monitoring and controlling a process. The process can be industrial, infrastructure or facility based as described below:

Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.

Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, and large communication systems.

Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control HVAC, access, and energy consumption.

A SCADA System usually consists of the following subsystems:

A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator monitors and controls the process.

A supervisory (computer) system, gathering (acquiring) data on the process and sending commands (control) to the process

Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.

Communication infrastructure connecting the supervisory system to the Remote Terminals Units

There is, in several industries, considerable confusion over the differences between SCADA systems and Distributed control systems (DCS). Generally speaking, a SCADA system usually refers to a system that coordinates, but does not control processes in real time. The discussion on real-time control is muddied somewhat by newer telecommunications technology, enabling reliable, low latency, high speed communications over wide areas. Most differences between SCADA and Distributed control system DCS are culturally determined and can usually be ignored. As communication infrastructures with higher capacity become available, the difference between SCADA and DCS will fade.

Systems concepts

The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything between an industrial plant and a country). Most control actions are performed automatically by remote terminals units (”RTUs”) or by programmable logic controllers (”PLCs”). Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop.

Data acquistion begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required. Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either “hard” or “soft”. A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. (Most implementations conceptually remove the distinction by making every property a “soft” point expression, which may, in the simplest case, equal a single hard point.) Points are normally stored as value-timestamp pairs: a value, and the timestamp when it was recorded or calculated. A series of value-timestamp pairs gives the history of that point. It’s also common to store additional metadata with tags, such as the path to a field device or PLC register, design time comments, and alarm information.

Human Machine Interface

A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator controls the process.

An HMI is usually linked to the SCADA system’s databases and software programs, to provide trending, diagnostic data, and management information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides.

The HMI system usually presents the information to the operating personnel graphically, in the form of a mimic diagram. This means that the operator can see a schematic representation of the plant being controlled. For example, a picture of a pump connected to a pipe can show the operator that the pump is running and how much fluid it is pumping through the pipe at the moment. The operator can then switch the pump off. The HMI software will show the flow rate of the fluid in the pipe decrease in real time. Mimic diagrams may consist of line graphics and schematic symbols to represent process elements, or may consist of digital photographs of the process equipment overlain with animated symbols.

The HMI package for the SCADA system typically includes a drawing program that the operators or system maintenance personnel use to change the way these points are represented in the interface. These representations can be as simple as an on-screen traffic light, which represents the state of an actual traffic light in the field, or as complex as a multi-projector display representing the position of all of the elevators in a skyscraper or all of the trains on a railway.

An important part of most SCADA implementations are alarms. An alarm is a digital status point that has either the value NORMAL or ALARM. Alarms can be created in such a way that when their requirements are met, they are activated. An example of an alarm is the “fuel tank empty” light in a car. The SCADA operator’s attention is drawn to the part of the system requiring attention by the alarm. Emails and text messages are often sent along with an alarm activation alerting managers along with the SCADA operator.

Hardware solutions

SCADA solutions often have Distributed Control System (DCS) components. Use of “smart” RTUs or PLCs, which are capable of autonomously executing simple logic processes without involving the master computer, is increasing. A functional block programming language, IEC 61131-3, is frequently used to create programs which run on these RTUs and PLCs. Unlike a procedural language such as the C programming language or FORTRAN, IEC 61131-3 has minimal training requirements by virtue of resembling historic physical control arrays. This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC. Since about 1998, virtually all major PLC manufacturers have offered integrated HMI/SCADA systems, many of them using open and non-proprietary communications protocols. Numerous specialized third-party HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also entered the market, allowing mechanical engineers, electrical engineers and technicians to configure HMIs themselves, without the need for a custom-made program written by a software developer.

Remote Terminal Unit (RTU)

The RTU connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting digital setpoints to electrical signals and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump.

Quality SCADA RTUs have these characteristics:

Data Networking capability

Data Reliability

Data Security.

Supervisory Station

The term “Supervisory Station” refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc), and then to the HMI software running on workstations in the control room, or elsewhere. In smaller SCADA systems, the master station may be composed of a single PC. In larger SCADA systems, the master station may include multiple servers, distributed software applications, and disaster recovery sites. To increase the integrity of the system the multiple servers will often be configured in a dual-redundant or hot-standby formation providing continuous control and monitoring in the event of a server failure.

Initially, more “open” platforms such as Linux were not as widely used due to the highly dynamic development environment and because a SCADA customer that was able to afford the field hardware and devices to be controlled could usually also purchase UNIX or OpenVMS licenses. Today, all major operating systems are used for both master station servers and HMI workstations.

Operational philosophy

For some installations, the costs that would result from the control system failing is extremely high. Possibly even lives could be lost. Hardware for some SCADA systems is ruggedized to withstand temperature, vibration, and voltage extremes, but in most critical installations reliability is enhanced by having redundant hardware and communications channels, up to the point of having multiple fully equipped control centres. A failing part can be quickly identified and its functionality automatically taken over by backup hardware. A failed part can often be replaced without interrupting the process. The reliability of such systems can be calculated statistically and is stated as the mean time to failure, which is a variant of mean time between failures. The calculated mean time to failure of such high reliability systems can be on the order of centuries.

Communication infrastructure and methods

SCADA systems have traditionally used combinations of radio and direct serial or modem connections to meet communication requirements, although Ethernet and IP over SONET / SDH is also frequently used at large sites such as railways and power stations. The remote management or monitoring function of a SCADA system is often referred to as telemetry.

This has also come under threat with some customers wanting SCADA data to travel over their pre-established corporate networks or to share the network with other applications. The legacy of the early low-bandwidth protocols remains, though. SCADA protocols are designed to be very compact and many are designed to send information to the master station only when the master station polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570, Profibus and Conitel. These communication protocols are all SCADA-vendor specific but are widely adopted and used. Standard protocols are IEC 60870-5-101 or 104, IEC 61850 and DNP3. These communication protocols are standardized and recognized by all major SCADA vendors. Many of these protocols now contain extensions to operate over TCP/IP. It is good security engineering practice to avoid connecting SCADA systems to the Internet so the attack surface is reduced.

RTUs and other automatic controller devices were being developed before the advent of industry wide standards for interoperability. The result is that developers and their management created a multitude of control protocols. Among the larger vendors, there was also the incentive to create their own protocol to “lock in” their customer base. A list of automation protocols is being compiled here.

Recently, OLE for Process Control (OPC) has become a widely accepted solution for intercommunicating different hardware and software, allowing communication even between devices originally not intended to be part of an industrial network.

Trends in SCADA

There is a trend for PLC and HMI/SCADA software to be more “mix-and-match”. In the mid 1990s, the typical DAQ I/O manufacturer supplied equipment that communicated using proprietary protocols over a suitable-distance carrier like RS-485. End users who invested in a particular vendor’s hardware solution often found themselves restricted to a limited choice of equipment when requirements changed (e.g. system expansions or performance improvement). To mitigate such problems, open communication protocols such as IEC870-5-101/104 and DNP 3.0 (serial and over IP) became increasingly popular among SCADA equipment manufacturers and solution providers alike. Open architecture SCADA systems enabled users to mix-and-match products from different vendors to develop solutions that were better than those that could be achieved when restricted to a single vendor’s product offering.

Towards the late 1990s, the shift towards open communications continued with individual I/O manufacturers as well, who adopted open message structures such as Modbus RTU and Modbus ASCII (originally both developed by Modicon) over RS-485. By 2000, most I/O makers offered completely open interfacing such as Modbus TCP over Ethernet and IP.

SCADA systems are coming in line with standard networking technologies. Ethernet and TCP/IP based protocols are replacing the older proprietary standards. Although certain characteristics of frame-based network communication technology (determinism, synchronization, protocol selection, environment suitability) have restricted the adoption of Ethernet in a few specialized applications, the vast majority of markets have accepted Ethernet networks for HMI/SCADA.

“Next generation” protocols such as OPC-UA, Wonderware’s SuiteLink, GE Fanuc’s Proficy and Rockwell Automation’s FactoryTalk, take advantage of XML, web services and other modern web technologies, making them more easily IT supportable.

With the emergence of software as a service in the broader software industry, a few vendors have begun offering application specific SCADA systems hosted on remote platforms over the Internet, for example, PumpView by MultiTrode. This removes the need to install and commission systems at the end-user’s facility and takes advantage of security features already available in Internet technology, VPNs and SSL. Some concerns include security, Internet connection reliability, and latency.

SCADA systems are becoming increasingly ubiquitous. Thin clients, web portals, and web based products are gaining popularity with most major vendors. The increased convenience of end users viewing their processes remotely introduces security considerations.

Security issues

The move from proprietary technologies to more standardized and open solutions together with the increased number of connections between SCADA systems and office networks and the Internet has made them more vulnerable to attacks. Consequently, the security of SCADA-based systems has come into question as they are increasingly seen as extremely vulnerable to cyberwarfare/cyberterrorism attacks.

In particular, security researchers are concerned about:

the lack of concern about security and authentication in the design, deployment and operation of existing SCADA networks

the mistaken belief that SCADA systems have the benefit of security through obscurity through the use of specialized protocols and proprietary interfaces

the mistaken belief that SCADA networks are secure because they are purportedly physically secured

the mistaken belief that SCADA networks are secure because they are supposedly disconnected from the Internet

Because of the mission-critical nature of a large number of SCADA systems, such attacks could, in a worst case scenario, cause massive financial losses through loss of data or actual physical destruction, misuse or theft, even loss of life, either directly or indirectly. Whether such concerns will cause a move away from the use of existing SCADA systems for mission-critical applications towards more secure architectures and configurations remains to be seen, given that at least some influential people in corporate and governmental circles believe that the benefits and lower initial costs of SCADA based systems still outweigh potential costs and risks] Recently, multiple security vendors, such as Byres Security, Inc., Industrial Defender Inc., Check Point and Innominate, and N-Dimension Solutions have begun to address these risks by developing lines of specialized industrial firewall and VPN solutions for TCP/IP-based SCADA networks. The problem according to Eric Byres, CEO of Byres Security, is that “while many infrastructure organizations are doing good work, others are falling behind. When you have this diversity of effort, you are only as effective as your weakest link.

Also, the ISA Security Compliance Institute (ISCI) is emerging to formalize SCADA security testing starting as soon as 2009. ISCI is conceptually similar to private testing and certification that has been performed by vendors since 2007, such as the Achilles certification program from Wurldtech Security Technologies, Inc. and MUSIC certification from Mu Security, Inc. Eventually, standards being defined by ISA SP99 WG4 will supersede these initial industry consortia efforts, but probably not before 2011.

N.Sankari
http://www.articlesbase.com/electronics-articles/introduction-to-plc-and-scada-679975.html

Introduction to PLC’s

Programmable Logic Controllers

Bedford Associates, founded by Richard Morley introduced the first Programmable Logic Controller in 1968. This PLC was known as the Modular Digital Controller from which the MODICON company derived its name. The History of the PLC as told to Howard Hendricks by Dick Morley provides an interesting insight into the early development of the PLC.

Schnieder Quantum PLC

Programmable Logic Controllers were developed to provide a replacement for large relay based control panels. These systems were inflexible requiring major rewiring or replacement whenever the control sequence was to be changed.

The development of the micro processor from the mid 1970’s have allowed Programmable Logic Controllers to take on more complex tasks and larger functions as the speed of the processor increased.

Ladder Logic

PLC had to be maintainable by technicians and electrical personnel. To support this the programming language of Ladder Logic was developed. Ladder Logic is based on the relay and contact symbols technicians were used to through wiring diagrams of electrical control panels.

Until recently there has been no formal programming standard for PLC’s. The introduction of the IEC 61131 Standard in 1998 provides a more formal approach to coding. PLC Manufacturers have so far been slow on the uptake of the standard with partial implementation. The SearchEng articleIEC 61131-3, a Standard for PLC Software by R.W. Lewis provides an introduction to the standard.

The documentation for early PLC Programs was either non existent or very poor, just providing simple addressing and basic comments, making large programs difficult to follow. This has been greatly improved with the development of PLC Programming Packages.

SCADA and HMI

The early programmable logic controllers interfaced with the operator in much the same way as the relay control panel, via push-buttons and switches for control and lamps for indication.

The introduction of the Personal Computer (PC) in the 1980’s allowed for the development of a computer based interface to the operator, these where initially via simple Supervisory Control and Data Acquisition (SCADA) systems and more recently via Dedicated Operator Control Panels, known as Human Machine Interfaces (HMI).

The History of the PLC
as told to Howard Hendricks by Dick Morley

The following are some fables associated with the first ten years of the programmable controller business. These Fables may or may not have a basis of truth, but in general, they are the best that my Alzheimer-plagued memory can do at the moment. As has been often in other articles and reports, the startup of Modicon and the programmable controller industry as a whole is well documented. The programmable controller was detailed on New Year’s Day, 1968, and from hence till now, a slow steady growth has allowed the manufacturing and process control industries to take advantage of applications-oriented software.

The early days however, were not as straightforward nor as simple. We had some real problems in the early days of convincing people that a box of software, albeit cased in cast iron, could do the same thing as 50 feet of cabinets, associated relays and wiring. The process was indeed difficult, and deserves some of the stories that I hope the reader will be regaled with as he proceeds onward through the tortuous swamp of my mind.

One of my earliest recommendations was that the programmable controller, according to my own system architecture specification, did not need to go fast because I felt as though speed was not a criteria because it would go as fast as we needed it to. The initial machine, which was never delivered, only had 125 words of memory, and speed was not a criteria as mentioned earlier. You can imagine what happened! First, we immediately ran out of memory, and second, the machine was much too slow to perform any function anywhere near the relay response time. Relay response times exist on the order of 1/60th of a second, and the topology formed by many cabinets full of relays transformed to code is significantly more than 125 words. We expanded the memory to 1K and thence to 4K. At 4K, it stood the test of time for quite a while. Initially, marketing and memory sizes were sold in 1K, 2K, 3K, (?) and 4K. the 3K was obviously the 4K version with constrained address so that field expansion to 4K could easily be done.

The question of speed, in part, was part of the early designs. No interrupts were necessary because the external signal conditions were directly written onto memory without any supervisory requirements or “operating system of the conventional type. This allowed the processor to pay attention to solving logic rather than housekeeping the I/O. As a result, of course, the processor had to have significantly more processing power than normally associated with this size computer; and secondly, the system had to be made to run fast.

We increased the memory size, as mentioned above, but to get it to run fast, we had to break up the machine into three distinct components. Initially, the programmable controller was conceived of a processor board and a memory, and that the algorithmic and logical manipulation would be done in software. This approach was painfully slow, both on the generic “store bought computers, and other items.

We did, however, manage to substantially speed up the machine by making a third major component. This was called the logic solver. A logic solver board solved the dominant algorithms associated with solving ladder logic without the intervention and classical software approach of general-purpose processing. This meant that we ended up with three boards; memory, logic solver and processor. This single step allowed us to get the speed we needed in this application-specific computer to solve the perceptually simple problem of several cabinets full of relay wiring.

We had also assumed a modular approach to the programmable controller. In act, the name Modicon means MOdular DIgital CONtroller. The modularity, however, was soon abandoned because, as everyone knows, open architectures are no good. We instead had the marketing premise that a large footprint would contain within it the sets of problems we wished to solve. This meant that a buyer of programmable controllers could buy large numbers of the same units, and the software and hardware would be identical across a broad spectrum of applications in his factory. Service, maintenance and total life cost would be substantially lower than the perceived lower cost of an open architecture and modular expansion. Although at first, a supporter of the open architecture modular expansion, I soon became convinced by the marketplace, but this was folly.

We took one of our early units which was aimed at the machine tool industry because of my Bedford Associates consulting background, up to one of the early requesters of this equipment. This particular early requester was Byrant Chuck and Grinder in Springfield, Vermont. We took the machine up there, and it was heavy. This was the 084. The 084 was in the trunk of my old Pontiac, and since we needed help carrying it in, requested some of the people at Bryant to help us. We went out and opened the hood, and the first comment made by an outside viewer of the programmable controller said, “Thank God it,s not another pastel colored piece of sheet metal.

We can hypothesize from this particular comment that the ruggedness of the visual design was pleasing to him, and being human (as opposed to Martian), assumed that this same attitude went deep inside the construction of the machine in both the hardware and software. Indeed, this was the case, and the machine as a result, was built rugged, had no ON/OFF switch, had no fans, did not make any noise and had no wear out system.

To reminisce for a moment—in selecting the cores for the first memories, which in itself was a revolutionary step, we selected these cores and we applied Shannon,s Law. Shannon,s Law assumes that the signal-to-noise ratio is what makes signals good or bad. There are several ways to get the power from the signal-to-noise ratio; one is to code heavily, be triply redundant, and use lots and lots of error checking. There is another way, which is perfectly compatible with theory, which is to use lots of signal power in another domain. A nice switch, a car battery and a D-rated light bulb will work fairly well over a long time period.

Therefore, what we did was rather than going error checking, triply redundant and stuff, we got, and searched for and found high energy, large ferrite core memories that had lots on energy per bit. We still make the same assumption today. The energy per bit is extremely important—as Shannon,s theory said in his most famous 1948 paper, that the signal noise to power noise is what gives you transmission. the way we got signal power was to increase the energy per bit. This we felt was far more important than getting the energy per bit increased by means of doubly transmitting it. But I digress. Bryant Chuck and Grinder put it in, and liked the equipment so much that they never bought one. They in turn thought it was a good idea, and as many did at that time, tried to evolve their own.

One of our first major customers, however, was Landis in Landis, PA. We flew the equipment down in a private aircraft, and with apprehension because we were late (as usual), brought the equipment into Landis. In doing so, we tripped over the threshold. The equipment went KA-RASH onto the floor! Without much chagrin, we picked the equipment up, trundled it in. hooked it up, and low and behold, it worked quite well.

Now, Landis was pleased and surprised. They were pleased because it worked, but they were most pleasantly surprised—not because the equipment worked—but because the guys from Modicon fully expected the equipment to work in spite of it being dropped. In other words, the people from Modicon weren,t nervous about the fact that it fell on the floor over the threshold.

Landis subsequently took and wrapped welding coils of wire around the machine to induce electro-magnetic noise to see if they could make it fail. We had them there! We used to test the programmable controllers with a Teslar coil that struck a quarter inch to half-inch arch anywhere on the system, and the programmable controller still had to continue to run. There was significant strangeness with respect to the programmable controller. For example, it had no ON/OFF switch. It had no means to load software. It had no fans. It ran cool. It could survive bad, physical and thermal environments. It was not computer industry standard. There were many things that were most difficult in the acceptance of the programmable controller, and early acceptance was most difficult indeed.

Our sales in the first four years were abysmal. Early innovators such as Landers and General Motors were, of course, heroes to our eyes, but they would buy small numbers of units and then test them in the field before they committed themselves later on. We had one customer in the utilities business that took them approximately six to seven years to make a decision to but the first one.

We never really sold any programmable controllers into the intended market which was machine tool control such as lathes, grinders and stuff, but we did, as luck would have it, stumble across the transfer line market which was and still is the mainstay, long-term market for the application of programmable controllers. Discreet parts manufacturing in an automatic environment, i.e., mass production, continues to be, and probably will be for the future, the mainstay of the programmable controller industry.

Some of the more interesting stories center around the personalities and experiences as opposed to the programmable controller. Modicon,s third president (or fourth, if you count my two-week stint) was Don Kramer. When Don Kramer was chosen as president, we decided to go out and celebrate at the Lanum Club in Andover. At the time, we felt we should celebrate over both martinis and food. As we were leaving the shop for the Lanum Club, Don made the aside comment that “the place is dingy and needs a paint job. As we were leaving, I mentioned to Don that as president you have to change what you say, and not be very open—you have to be a little careful about what you say because employees, customers, and boards of directors tend to take what you say as truth. Rather than listen to the meaning, they listen to the literal statements, and one must be careful. We went over to the Lanum Club and had a nice glowing two hours of discussion, food, and drink. Coming back, as we entered the Modicon lobby, we noticed that there was scaffolding about and people were painting. We went over and asked Lou as to why these people are painting since, at the time, we don,t have any money. Who ordered this paint job? And Lou looked Don Kramer straight in the eye, and said, “Why you did, Mr. Kramer. Nuff said.

As has been mentioned many times, your author, that,s me—Dick Morley—is supposed to be the inventor of the programmable controller. This is at best, partially true. The thing that made the Modicon company and the programmable controller really take off was not the 084, but the 184. The 184 was done in design cycle by Michael Greenberg, one of the best engineers I have ever met. He, and Lee Rousseau, president and marketeer, came up with a specification and a design that revolutionized the automation business. they built the 184 over the objections of yours truly. I was a purist and felt that all those bells and whistles and stuff weren,t “pure, and somehow they were contaminating my “glorious design, Dead wrong again, Morley! they were specifically right on! the 184 was a walloping success, and it—not the 084, not the invention of the programmable controller—but a product designed to meet the needs of the marketplace and the customer, called the 184, took off and made Modicon and the programmable controller the company and industry it is today. My compliments to the two chefs—Lee Rousseau and Mike Greenberg.

The issue of quality in programmable controllers is a story that is normally taken for granted. The gentle reader must remember that our engineering people came from the computer industry where reliability in those days was a phantom—a phantom of design, a phantom of cost. People felt that reliability was something other people did, and that if we only could deliver faster computers, even if they didn,t work, everything would be fine.

When the programmable controller was designed, it was designed in to be reliable. We used lots of energy per information bit by utilizing D-rated components, large memory ferrite cores, relatively stable and large etchings on printed circuit boards, totally enclosed systems and conductive cooling. No fans were used, and outside air was not allowed to enter the system for fear of contamination and corrosion. Mentally, we had imagined the programmable controller being underneath a truck, in the open, and being driven around—driven around in Texas, driven around in Alaska. Under those circumstances, we anted it to survive. The other requirement was that it stood on a pole helping run an utility or a microwave station which was not climate controlled, and not serviced at all. Under those circumstances, would it work for the years that it was intended to be? Could it be walled in? Could it be bolted in a system that was expected to last 20 years?

The humorous side of this is though we did all those designs and very carefully tried to make this system as intrinsically reliable as we could, not by redundancy, but by building well. In other words, it was designed to be built, it was designed to be designed, and it was designed to be reliable. We, however, as engineers, didn,t understand the accountants and manufacturing. those two have their grail, shipments by the end of the month. As far as we could ascertain at the time, shipments were made independent of quality and independent of whether or not the system ran.

In the early days of the programmable controller and Modicon, even though I wasn,t a direct employee and an owner, I would give out my home phone number to many of our critical customers so that if they had a problem, they could call me directly. Several calls indicated that when we shipped near the end of the month, let’s say October 34th, that the equipment would not run; and secondly, when they opened the box and took the machine apart, cards were missing, bolts were on the bottom of the cabinetry, and some of the cards were not fully inserted. In other words, to make the end of the month was much more important than to deliver equipment that ran. to put it mildly, we were pissed! How do we as engineers maintain quality without continual surveillance which is most difficult for the design and entrepreneurial mind set. What we did was specify and design “blue boxes. These were cabinetries that the system had to operate in and run continuously for a minimum of 24 hours, under load, and under varying conditions. The box was built out of plywood, but its primary intention was to heat cycle the programmable controller under various input/output loads. We also ran, as a specification, that a Tesla coil was to be used on the programmable controller, and that vibration and thumping with a hammer (rubber) would be part of the specification.

This may seem unscientific to many of you, but let us assume that you try to get your equipment to run while somebody purposely tries to destroy it with a rubber hammer or spark coil that he can put anywhere on the system. Remember, your intention is to make the processor stop. That combination significantly depressed those monthly shipments during the first period. As a result of that, however, the message got through. Not only did we build ovens and tests, and pay attention to heat and spark and RF emissions, we would run the system continuously even in the shipping crate to get the maximum number of pre-custom hours we could. It was important to us that we found the mistakes and not the customer and his secondary customer.

The language itself, ladder lister, bears some discussion. This particular language was not the invention of Modicon. We hypothesize that the language is very old, and originated in Germany to describe relay circuitry. If one looks at ladder lister, it has been our technical community for so long, we somehow think those little symboligies actually look like relays. In fact, it,s a mnemonic form of rule-based language, very modern and very high level, but designed in a Darwinian fashion over a period of many decades.

The ladder logic construct, “If… Then… is a very powerful construct used today in expert systems and other rule-based languages. The symbology, allowing normally open and normally closed situations as well as parallel and serial representation, was used for many decades before the invention of the programmable controller. I have worked on machines where the number of C-size and D-size prints were hung in special racks, and would be up to three feet thick worth of documentation on those drawing sets.

The name ladder comes from the fact that on the right-hand of the drawing is one power rail and the left-hand side is the other power rail; and in between in a horizontal fashion, is the statement or sequential connection of logical elements which we call relays or relay logic. The initial 084 had only logic in its functionality, and as a result, was marginal. In other words, all we did was replace relays rather than enhance the functionality by a factor of ten which is the entrepreneurial rule. Immediately, of course, based on customer response and our own frustrations, we put thing in the ladder listing language such as addition, multiplication, subtraction, and other functionalities that went far beyond relay capability and entered the realm of mathematics and set theory. This was still not sufficient, however, and we needed some way to make a “call to a “subroutine using ladder lister symbology and representation.

A software engineer, Chuck Schelberg, and myself were in the conference room one day trying to ascertain how we could make a generic call to functionalities that far exceeded the relay symbology and representation, and came up with the “DX function. This function was a block function that would be an element on the ladder logic representation that could perform many functionalities including arrays, motor drive functions, servo functions, extended mathematical functions, PID loops, ad nauseam. We felt there would be an occasional representation and use of these functionalities, and that not much had to be done to the programmable controller other than to modify the software. Wrong again!

The first customer that took delivery of a programmable controller utilizing the DX function, had a capability to be predictable and operate in real time. The RUN light went out, and the time to execute a scan or complete transformation of the ladder logic went far beyond the time allowable. Every single line had a DX function on it. Again we learned that when you enhance functionality, people use it all. I have never designed a computer that had too much memory. I,ve only designed computers that have too little memory. The same thing applies to any other functionality. Conventional wisdom seems to think that price/performance depends on only one thing—price—when, in fact, my experience has been that the customer cares little about price.

This price/performance tirade being over, one of the lessons we learned is that the customer wants functionality over the entire life cycle cost installation of the job. the customer also wants ease of installation, to have some fun, and to be proud of the work he does. After he,s finished, he never wants to come back.. The equipment should work as installed and as based. At one time, the programmable controller meantime before failure in the field was 50,000 hours. This is far in excess of almost any other type of electronic or control equipment.

The concept of languages and high-level languages is important. The programmable controller, as it evolved, began to request more and more power, and more and more memory. The memories continually went up as well as power. It is estimated that at one time, in the mid-1970s, that the programmable controller had the equivalent of two MIPS processor and 128 kilobytes of memory, which at that time was a significantly powered minicomputer capability. Why? High-level languages require power to run them. If we take the equivalent of the ladder lister statement “If… Then…, the high-level language as represented here, requires a substantial amount of interpretive compiler, if you will, generation of underlying code. In other words, this statement spawns significant underlying code that must be run quickly, reliably, and contain within it, all aspects of resource allocation and operations resource. The higher level the language, the more powerful the processor apparently has to be in order to run the language. Ladder lister is a high-level rule-based language which, until now, we haven,t talked much about in these terms. Our customers treated the programmable controller as a box of relays, and well they should. Language theory is neither necessary not desirable for most of the customers to know. The customers, instead, understand their problem, and are indeed much smarter than the design engineers because the dimensions of their problem far exceed the relatively simple problem of designing a computer software system and language. Ladder lister requires high performance which is one of the reasons it has difficulty running on the personal computer even of today

INTRODUCTION TO SCADA

SCADA is the abbreviation for Supervisory Control And Data Acquisition. It generally refers to an industrial control system: a computer system monitoring and controlling a process. The process can be industrial, infrastructure or facility based as described below:

Industrial processes include those of manufacturing, production, power generation, fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.

Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, and large communication systems.

Facility processes occur both in public facilities and private ones, including buildings, airports, ships, and space stations. They monitor and control HVAC, access, and energy consumption.

A SCADA System usually consists of the following subsystems:

A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator monitors and controls the process.

A supervisory (computer) system, gathering (acquiring) data on the process and sending commands (control) to the process

Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.

Communication infrastructure connecting the supervisory system to the Remote Terminals Units

There is, in several industries, considerable confusion over the differences between SCADA systems and Distributed control systems (DCS). Generally speaking, a SCADA system usually refers to a system that coordinates, but does not control processes in real time. The discussion on real-time control is muddied somewhat by newer telecommunications technology, enabling reliable, low latency, high speed communications over wide areas. Most differences between SCADA and Distributed control system DCS are culturally determined and can usually be ignored. As communication infrastructures with higher capacity become available, the difference between SCADA and DCS will fade.

Systems concepts

The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything between an industrial plant and a country). Most control actions are performed automatically by remote terminals units (”RTUs”) or by programmable logic controllers (”PLCs”). Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop.

Data acquistion begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required. Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either “hard” or “soft”. A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. (Most implementations conceptually remove the distinction by making every property a “soft” point expression, which may, in the simplest case, equal a single hard point.) Points are normally stored as value-timestamp pairs: a value, and the timestamp when it was recorded or calculated. A series of value-timestamp pairs gives the history of that point. It’s also common to store additional metadata with tags, such as the path to a field device or PLC register, design time comments, and alarm information.

Human Machine Interface

A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator controls the process.

An HMI is usually linked to the SCADA system’s databases and software programs, to provide trending, diagnostic data, and management information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides.

The HMI system usually presents the information to the operating personnel graphically, in the form of a mimic diagram. This means that the operator can see a schematic representation of the plant being controlled. For example, a picture of a pump connected to a pipe can show the operator that the pump is running and how much fluid it is pumping through the pipe at the moment. The operator can then switch the pump off. The HMI software will show the flow rate of the fluid in the pipe decrease in real time. Mimic diagrams may consist of line graphics and schematic symbols to represent process elements, or may consist of digital photographs of the process equipment overlain with animated symbols.

The HMI package for the SCADA system typically includes a drawing program that the operators or system maintenance personnel use to change the way these points are represented in the interface. These representations can be as simple as an on-screen traffic light, which represents the state of an actual traffic light in the field, or as complex as a multi-projector display representing the position of all of the elevators in a skyscraper or all of the trains on a railway.

An important part of most SCADA implementations are alarms. An alarm is a digital status point that has either the value NORMAL or ALARM. Alarms can be created in such a way that when their requirements are met, they are activated. An example of an alarm is the “fuel tank empty” light in a car. The SCADA operator’s attention is drawn to the part of the system requiring attention by the alarm. Emails and text messages are often sent along with an alarm activation alerting managers along with the SCADA operator.

Hardware solutions

SCADA solutions often have Distributed Control System (DCS) components. Use of “smart” RTUs or PLCs, which are capable of autonomously executing simple logic processes without involving the master computer, is increasing. A functional block programming language, IEC 61131-3, is frequently used to create programs which run on these RTUs and PLCs. Unlike a procedural language such as the C programming language or FORTRAN, IEC 61131-3 has minimal training requirements by virtue of resembling historic physical control arrays. This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC. Since about 1998, virtually all major PLC manufacturers have offered integrated HMI/SCADA systems, many of them using open and non-proprietary communications protocols. Numerous specialized third-party HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also entered the market, allowing mechanical engineers, electrical engineers and technicians to configure HMIs themselves, without the need for a custom-made program written by a software developer.

Remote Terminal Unit (RTU)

The RTU connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting digital setpoints to electrical signals and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump.

Quality SCADA RTUs have these characteristics:

Data Networking capability

Data Reliability

Data Security.

Supervisory Station

The term “Supervisory Station” refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc), and then to the HMI software running on workstations in the control room, or elsewhere. In smaller SCADA systems, the master station may be composed of a single PC. In larger SCADA systems, the master station may include multiple servers, distributed software applications, and disaster recovery sites. To increase the integrity of the system the multiple servers will often be configured in a dual-redundant or hot-standby formation providing continuous control and monitoring in the event of a server failure.

Initially, more “open” platforms such as Linux were not as widely used due to the highly dynamic development environment and because a SCADA customer that was able to afford the field hardware and devices to be controlled could usually also purchase UNIX or OpenVMS licenses. Today, all major operating systems are used for both master station servers and HMI workstations.

Operational philosophy

For some installations, the costs that would result from the control system failing is extremely high. Possibly even lives could be lost. Hardware for some SCADA systems is ruggedized to withstand temperature, vibration, and voltage extremes, but in most critical installations reliability is enhanced by having redundant hardware and communications channels, up to the point of having multiple fully equipped control centres. A failing part can be quickly identified and its functionality automatically taken over by backup hardware. A failed part can often be replaced without interrupting the process. The reliability of such systems can be calculated statistically and is stated as the mean time to failure, which is a variant of mean time between failures. The calculated mean time to failure of such high reliability systems can be on the order of centuries.

Communication infrastructure and methods

SCADA systems have traditionally used combinations of radio and direct serial or modem connections to meet communication requirements, although Ethernet and IP over SONET / SDH is also frequently used at large sites such as railways and power stations. The remote management or monitoring function of a SCADA system is often referred to as telemetry.

This has also come under threat with some customers wanting SCADA data to travel over their pre-established corporate networks or to share the network with other applications. The legacy of the early low-bandwidth protocols remains, though. SCADA protocols are designed to be very compact and many are designed to send information to the master station only when the master station polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570, Profibus and Conitel. These communication protocols are all SCADA-vendor specific but are widely adopted and used. Standard protocols are IEC 60870-5-101 or 104, IEC 61850 and DNP3. These communication protocols are standardized and recognized by all major SCADA vendors. Many of these protocols now contain extensions to operate over TCP/IP. It is good security engineering practice to avoid connecting SCADA systems to the Internet so the attack surface is reduced.

RTUs and other automatic controller devices were being developed before the advent of industry wide standards for interoperability. The result is that developers and their management created a multitude of control protocols. Among the larger vendors, there was also the incentive to create their own protocol to “lock in” their customer base. A list of automation protocols is being compiled here.

Recently, OLE for Process Control (OPC) has become a widely accepted solution for intercommunicating different hardware and software, allowing communication even between devices originally not intended to be part of an industrial network.

Trends in SCADA

There is a trend for PLC and HMI/SCADA software to be more “mix-and-match”. In the mid 1990s, the typical DAQ I/O manufacturer supplied equipment that communicated using proprietary protocols over a suitable-distance carrier like RS-485. End users who invested in a particular vendor’s hardware solution often found themselves restricted to a limited choice of equipment when requirements changed (e.g. system expansions or performance improvement). To mitigate such problems, open communication protocols such as IEC870-5-101/104 and DNP 3.0 (serial and over IP) became increasingly popular among SCADA equipment manufacturers and solution providers alike. Open architecture SCADA systems enabled users to mix-and-match products from different vendors to develop solutions that were better than those that could be achieved when restricted to a single vendor’s product offering.

Towards the late 1990s, the shift towards open communications continued with individual I/O manufacturers as well, who adopted open message structures such as Modbus RTU and Modbus ASCII (originally both developed by Modicon) over RS-485. By 2000, most I/O makers offered completely open interfacing such as Modbus TCP over Ethernet and IP.

SCADA systems are coming in line with standard networking technologies. Ethernet and TCP/IP based protocols are replacing the older proprietary standards. Although certain characteristics of frame-based network communication technology (determinism, synchronization, protocol selection, environment suitability) have restricted the adoption of Ethernet in a few specialized applications, the vast majority of markets have accepted Ethernet networks for HMI/SCADA.

“Next generation” protocols such as OPC-UA, Wonderware’s SuiteLink, GE Fanuc’s Proficy and Rockwell Automation’s FactoryTalk, take advantage of XML, web services and other modern web technologies, making them more easily IT supportable.

With the emergence of software as a service in the broader software industry, a few vendors have begun offering application specific SCADA systems hosted on remote platforms over the Internet, for example, PumpView by MultiTrode. This removes the need to install and commission systems at the end-user’s facility and takes advantage of security features already available in Internet technology, VPNs and SSL. Some concerns include security, Internet connection reliability, and latency.

SCADA systems are becoming increasingly ubiquitous. Thin clients, web portals, and web based products are gaining popularity with most major vendors. The increased convenience of end users viewing their processes remotely introduces security considerations.

Security issues

The move from proprietary technologies to more standardized and open solutions together with the increased number of connections between SCADA systems and office networks and the Internet has made them more vulnerable to attacks. Consequently, the security of SCADA-based systems has come into question as they are increasingly seen as extremely vulnerable to cyberwarfare/cyberterrorism attacks.

In particular, security researchers are concerned about:

the lack of concern about security and authentication in the design, deployment and operation of existing SCADA networks

the mistaken belief that SCADA systems have the benefit of security through obscurity through the use of specialized protocols and proprietary interfaces

the mistaken belief that SCADA networks are secure because they are purportedly physically secured

the mistaken belief that SCADA networks are secure because they are supposedly disconnected from the Internet

Because of the mission-critical nature of a large number of SCADA systems, such attacks could, in a worst case scenario, cause massive financial losses through loss of data or actual physical destruction, misuse or theft, even loss of life, either directly or indirectly. Whether such concerns will cause a move away from the use of existing SCADA systems for mission-critical applications towards more secure architectures and configurations remains to be seen, given that at least some influential people in corporate and governmental circles believe that the benefits and lower initial costs of SCADA based systems still outweigh potential costs and risks] Recently, multiple security vendors, such as Byres Security, Inc., Industrial Defender Inc., Check Point and Innominate, and N-Dimension Solutions have begun to address these risks by developing lines of specialized industrial firewall and VPN solutions for TCP/IP-based SCADA networks. The problem according to Eric Byres, CEO of Byres Security, is that “while many infrastructure organizations are doing good work, others are falling behind. When you have this diversity of effort, you are only as effective as your weakest link.

Also, the ISA Security Compliance Institute (ISCI) is emerging to formalize SCADA security testing starting as soon as 2009. ISCI is conceptually similar to private testing and certification that has been performed by vendors since 2007, such as the Achilles certification program from Wurldtech Security Technologies, Inc. and MUSIC certification from Mu Security, Inc. Eventually, standards being defined by ISA SP99 WG4 will supersede these initial industry consortia efforts, but probably not before 2011.

N.Sankari
http://www.articlesbase.com/electronics-articles/introduction-to-plc-and-scada-679975.html

You’ve probably seen the adverts on television for Sheilas’ Wheels car insurance, where three glamorous blonde women are sitting pretty in a bubblegum-pink car. These good-time girls are contrasted to a miserable group of Australian sheep station guys left out of this cheap women-only car insurance deal. Sisters are insuring it for themselves, the message is clear – they can get better deals. But is this female-friendly advertising just another marketing ploy or is their a real benefit for female motorists?

Most insurance companies recognise that women are cheaper to insure and their policy costs reflect this. Certainly this is the case until women reach middle age, according to research by the AA (based on quotes for men and women, driving a Ford Focus and living in Cambridgeshire). For young drivers, age 17, the insurance cost for a woman is £1,938.13 per annum, for men this figure rises by almost £1,000 to £2,906.25. At age 30, the cost for women is still over £40 cheaper at £367. By the age of 40 the saving falls to just over £7. For men and women of 50 years old, the cost for women is just 45 pence cheaper. And by the age of 60, men (for the first time) can enjoy a £7.30 advantage over their female counterparts when their insurance premium reaches £245.40.

The promise of cheaper deals is founded on the fact that, on average, women don’t have as many serious accidents and therefore should be less risky and less expensive drivers to insure.

There is also clear evidence that as regards appalling driving, men are way out in front. Annual statistics from the Home Office reveal that almost three quarters of speeding offences, 96% of dangerous driving offences and 85% of careless driving were committed by men.

Sheilas’ Wheels also markets the idea that car insurance can be tailored to women’s individual needs. It can provide £300 for handbag insurance for example, in addition to offering a counselling line after accidents and the promise of repair practices that are women-friendly. Those that ensure that cars can be available to be collected from garages in daylight or in time for a daily school run.

Pioneer of car insurance for women, Diamond (part of the Admiral group) believes that dedicated services for women form part of a wider social change. The majority of women now have a driving licence (61 per cent of women compared to just over four fifths of men) and insurance that is female friendly and /or exclusively for females is a question of independence which mirrors the rise in the number of single female households and women who own their own car.

Certainly, companies like Sheilas’ Wheels and Diamond are offer some of the cheapest deals in the marketplace but other, non-specialist companies disagree that gender- specific insurance gives the consumer much extra. They warn that these brands are just part of a clever advertising campaign. Sheilas’ Wheels, for instance isn’t even an Australian company but part of the HBOS group, which also includes esure, Halifax and Bank of Scotland.

It is true that it can be misleading to draw general conclusions about cheapness. Altering a few variables like occupation and age can reveal different results. Comparisons show that your postcode, for example, is far more significant than gender. Living in Liverpool can more than double the cost of your insurance whereas living in a rural, low-crime area such as Norfolk will bring the cost of your premiums right down.

The best advice is to check out exactly what is on offer from the insurers and see how it best meets your own individual requirements.

Michael Challiner
http://www.articlesbase.com/finance-articles/car-insurance-for-women-only-743267.html

You’ve probably seen the adverts on television for Sheilas’ Wheels car insurance, where three glamorous blonde women are sitting pretty in a bubblegum-pink car. These good-time girls are contrasted to a miserable group of Australian sheep station guys left out of this cheap women-only car insurance deal. Sisters are insuring it for themselves, the message is clear – they can get better deals. But is this female-friendly advertising just another marketing ploy or is their a real benefit for female motorists?

Most insurance companies recognise that women are cheaper to insure and their policy costs reflect this. Certainly this is the case until women reach middle age, according to research by the AA (based on quotes for men and women, driving a Ford Focus and living in Cambridgeshire). For young drivers, age 17, the insurance cost for a woman is £1,938.13 per annum, for men this figure rises by almost £1,000 to £2,906.25. At age 30, the cost for women is still over £40 cheaper at £367. By the age of 40 the saving falls to just over £7. For men and women of 50 years old, the cost for women is just 45 pence cheaper. And by the age of 60, men (for the first time) can enjoy a £7.30 advantage over their female counterparts when their insurance premium reaches £245.40.

The promise of cheaper deals is founded on the fact that, on average, women don’t have as many serious accidents and therefore should be less risky and less expensive drivers to insure.

There is also clear evidence that as regards appalling driving, men are way out in front. Annual statistics from the Home Office reveal that almost three quarters of speeding offences, 96% of dangerous driving offences and 85% of careless driving were committed by men.

Sheilas’ Wheels also markets the idea that car insurance can be tailored to women’s individual needs. It can provide £300 for handbag insurance for example, in addition to offering a counselling line after accidents and the promise of repair practices that are women-friendly. Those that ensure that cars can be available to be collected from garages in daylight or in time for a daily school run.

Pioneer of car insurance for women, Diamond (part of the Admiral group) believes that dedicated services for women form part of a wider social change. The majority of women now have a driving licence (61 per cent of women compared to just over four fifths of men) and insurance that is female friendly and /or exclusively for females is a question of independence which mirrors the rise in the number of single female households and women who own their own car.

Certainly, companies like Sheilas’ Wheels and Diamond are offer some of the cheapest deals in the marketplace but other, non-specialist companies disagree that gender- specific insurance gives the consumer much extra. They warn that these brands are just part of a clever advertising campaign. Sheilas’ Wheels, for instance isn’t even an Australian company but part of the HBOS group, which also includes esure, Halifax and Bank of Scotland.

It is true that it can be misleading to draw general conclusions about cheapness. Altering a few variables like occupation and age can reveal different results. Comparisons show that your postcode, for example, is far more significant than gender. Living in Liverpool can more than double the cost of your insurance whereas living in a rural, low-crime area such as Norfolk will bring the cost of your premiums right down.

The best advice is to check out exactly what is on offer from the insurers and see how it best meets your own individual requirements.

Michael Challiner
http://www.articlesbase.com/finance-articles/car-insurance-for-women-only-743267.html

Support Combat Wounded and Disabled Veterans
Donate my car – A guide to your vehicle donation qustions

About Purple Heart: The Military Order of the Purple Heart is a congressionally chartered non-profit organization that has been dedicated to helping veterans for over 70 years. Over 300,000 donors have trusted Purple Heart with their vehicle donation. In fact, many of our donors have found the donation process so convenient and rewarding that they have become repeat donors. Generous donors like you make it possible to assist our defenders of freedom in their time of need. Thank you for considering the Purple Heart.

Purple Heart Donation Information:

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- Purple Heart issues donors a tax-deductible donation receipt.

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- Purple Heart can arrange to have your vehicle towed or you may drive it to one of our facilities.

- Office hours are Monday through Friday 9AM to 6:30PM (EST) and Saturday 9AM to 5PM (EST).

– Boats, RV’s, and motorcycles are also accepted in most cases.

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For more information please visit our website. Purple Heart Cars

Site: www.phcars.org

phcars
http://www.articlesbase.com/non-profit-organizations-articles/purple-heart-car-donation-program-713835.html