This article begins our coverage of a new series of correspondence courses from Iowa State University. These courses are designed to meet state license renewal requirements and provide valuable information on a number of subjects.
See the accompanying sidebar, “Say Hello To Renewal Requirements,” and the sidebar below for details on the Iowa State program.
Closed-circuit television (CCTV) provides users with security and convenience. For both reasons, CCTV systems are very much in demand, and are an important market for the electrical and cabling industries.
A security-based installation is generally accomplished by placing cameras at critical locations to provide direct visual monitoring from a vantage point. Closed circuit television may be used on gates or other security areas not manned continuously. This system normally consists of a television camera, a monitor and electrical circuitry. The camera may be remotely controlled by monitoring security personnel.
Convenience-related use of CCTV on entry points includes the use of a two-way communication system between the monitor panel and the gate, and an electrically-operated gate lock. With this device, the person at the monitor panel can be alerted on the speaker system by a person desiring to enter, converse with the person, observe him on the monitor to determine his authority to enter, and then release the gate lock. An adaptation may be added to this equipment to enable the monitor personnel to make a side-by-side comparison of a person's face with the picture of his identification badge.
CCTV can also be used for surveillance of security cages, high value goods in warehouses, fence lines, movement of cargo and parking lots.
CCTV controls should be enclosed in metal housing and properly secured to prevent adjustment by unauthorized personnel. To avoid camera warm-up and adjustment delay, keep the camera in continuous operation.
Normally, surveillance TV is of the low-light level type (LLLTV) and can operate under marginal light conditions. A key consideration is maintenance of the TV system and supportive artificial lighting system.
Television operates by converting the visual image presented to a camera into an electronic signal, then sending the signal to a receiver. The electrical variations that correspond to changes in light values are called the video signal. At the receiver, the video signal is used to reassemble the video image, which is transformed back into visible light (by projecting a beam of electrons on a phosphor screen) at the picture tube.
Probably the easiest way to explain basic TV technology is to use the fax machine as an example. Our fax machines are properly called slow-scan television. They send one television picture frame, in black and white, over telephone lines. We are all familiar with the process: the machine scans one line at a time, interprets that area as black or white space, translates the information into electronic pulses, and transfers the information to a receiver.
Black-and-white television uses the same technology as the fax machine, except at 60 frames per second, and using a camera rather than a scanner. Each line of the image is scanned and translated into a complex video signal. The color process is the same, except a still more complex signal is used.
A video signal has several components. It is not necessary that you understand all of the electronic formulas that govern the operation of these signal components. You should, however, know what they are, and why they are used.
First is the scanning of each line. Television screens and images are divided into 525 scanning lines. If you could freeze a TV screen, you could work with a magnifying glass, and find that the image, from top to bottom, would be divided into 525 separate lines. This information is translated into electronic pulses, as mentioned above. HDTV has 1,125 lines, giving it much better definition. HDTV screens also have a significantly wider perspective — more like a movie screen.
When the first line is completely scanned, the automatic circuit moves on to the second line. To do this, however, special control signals must be added to the video signal.
One of these components is synch, which is a simple electronic marker that all the other signal components are anchored to.
Another is the blanking signal, which induces the receiver to cut off power to the screen while the electron beam switches from one line to another.
In order to put color in a television image another signal, called chroma, is used. By using combinations of red, blue and green color elements, virtually every color can be obtained on the television screen.
All of these signals are put together, making one composite signal.
Because of the complexity of the television signal, it requires a lot of bandwidth. Bandwidth is similar to speed — a low bandwidth is a lower frequency, and a higher bandwidth is a higher frequency. A standard TV channel uses 6 MHZ of bandwidth. In other words, the signal requires 6 million cycles per second (each cycle contributing part of the signal information) to get all of the information sent fast enough. We could send video images at lower speeds, but the images would be in slow motion.
To use multiple channels, each channel must use separate frequencies, or otherwise their signals would all be jumbled together. For example, the FCC has assigned channel 2 the frequency range of 54-60 MHZ, channel 3 has 60-66 MHZ, channel 4 has 66-72 MHZ and so on. (UHF channels go up to 890 MHZ.) Each channel transmits their programming in that 6 MHZ channel. Cable TV works the same way, except sending the signal through copper or optical fiber, not via radio waves.
One of the intimidating words used in the TV industry is modulation. Modulation is simply the function of taking a basic 6 MHZ TV signal and modifying it so that it matches one of the standard channel frequencies.
For example, the TV signal coming out of the camera at your local station operates at about 6 MHZ. If we assume that your station is channel 13, it must send its programs in the 210-216 MHZ slot. So, before sending the signal to the antenna, it must change the 6 MHZ signal to a 210-216 MHZ signal. This is done with a special electronic device called a modulator.
Your VCR has a modulator built into it. Since videotape cannot record the very high frequencies used in broadcasting (in the last example, the station used 216 MHZ), the VCR must record at frequencies that are too low for a television tuner to pick up. When you play a videotape, the information from the tape is modulated to channel 3 or 4, which your TV can then display.
Modulation is necessary in some circumstances, and not necessary in others. For example, modulators are not necessary with a single closed-circuit security camera. When using several cameras, however, all of the signals cannot use the same channel (they would overlap and distort one another), and they must be modulated to different channel frequencies.
Next month we will cover the components of video systems.
This year, Iowa State University has completely overhauled its electrical courses to meet state requirements. (See the accompanying sidebar, “Say Hello To Renewal Requirements.”) Eleven courses are now being offered and a Code Changes course will be added soon. Usually, one or two of these will meet the requirements in your state. The courses are:
National Electrical Code, 16 hours.
Code Refresher Course, 8 hours.
Electrical Controls, 4 hours.
Data Networking, 4 hours.
Fiber Optics, 4 hours.
Closed-Circuit TV Monitoring, 3 hours.
Mobile Homes and RV Parks, 2 hours.
Safety, 2 hours.
Worker's Compensation, 2 hours.
Electrical Business, 2 hours.
Electrical Theory, 2 hours.
Of course, you can take any of these courses at any time for your own improvement; but to meet your renewal requirements, you will have to take the courses that are required by your state.
Since the requirements for each state differ, a public Web site has been set up at www.ElectricRenewal.com. All registration information, course descriptions and state requirements can be found there. If you do not have Internet access, you can call the University office for this information at (800)262-0015 or fax the office at (515)294-6223.
Until very recently, the standard method of renewing an electrical license (journeyman, master, etc.) was simply to sign the form and send in a check. Not any more.
In the past few years, about half of U.S. states have instituted continuing education requirements for the renewal of electrical licenses.
If you haven't got “the letter” yet, get ready — you'll probably get it soon. In about half of the country, the new rule is: No continuing education credit-No license. (See related article on page 16.)
That depends entirely upon where you live. In many states, there are no requirements at all. At the moment, about 20 states do not have requirements. If the trend continues, however, soon only a handful will be left without continuing education requirements. Only a few years ago, Wyoming was the only state requiring continuing education. It has changed quickly.
The states that do require continuing education all have different requirements. All of them require some sort of course on the National Electrical Code. Some require eight hours of instruction and some more, some less. Some of the states require business courses, some require safety courses. (You can find the requirements for your state at www.ElectricRenewal.com.)
As of late 2001, the following states had continuing education requirements in place:
In addition, we are told that Arkansas, North Carolina and California may soon have renewal requirements.
Some of these states require continuing education for renewing contractor (or master) licenses only. Others require continuing education for journeyman licenses as well.
Actually, there are several ways.
First of all, traveling trainers lead seminars from time to time. If you live in a big city, they will probably visit your town at least once a year. The cost is usually in the $200-$500 range, and the training is generally quite good. Other expenses may also be associated with these seminars — attending them may require you to travel, miss a few days of work and perhaps stay one or two nights in a hotel.
Next are community college classes. These are generally affordable (in roughly the same price range as the seminars or a bit less), and the instruction is usually very good. The difficulty with these courses is that they take months to complete, and require you to spend one or two evenings per week driving to and from the school, hustling a burger somewhere in-between and missing time at home.
Correspondence training is excellent for fitting into your life (do it at any time that works for you), and allows you to work at your own pace. If you want to work the material a couple of hours per week, that's fine; and if you want to work through it all in a weekend, that's fine as well. The cost of correspondence training is usually a little bit less than the other methods, and if from a reputable provider, the training is very good. A few states do not allow correspondence training or offer limited credit for it.
Union programs vary from area to area, but they are usually good, and the cost is minimal. They are only given at certain times and places, so some travel or missing of work days may be required.
There are a few state programs, which are run by a state building department. The costs vary, and I have no information on the quality of their programs, except that I expect them to be at least reasonably good.
Are you looking for a home networking article that was published in a past issue of CEE News? Visit our Web site at www.ceenews.com to search for any of the previous Iowa State articles by Contributing Editor Paul Rosenberg.