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Fax Machines


How Fax Machines Work – Just the Facts

Office machines have become a very important part of our lives, both in the actual office, and at home. Almost every business has a printer, a photocopier and a fax machine. Fax machines are becoming as common as telephones. After all, they’re operated using telephone lines. And phone books even have listings of fax numbers now.

Most of us take fax machines for granted. We use them – but we don’t really know how they work. This article is designed to give you a working knowledge of fax machines. Then, as you use them, you’ll be able to say, “Hey, I know how that works.”

What is a fax machine?

“Fax” is a term we’ve coined from “facsimile machine”. Simply put, a fax machine is a device that can send or receive pictures and text over a telephone line. Fax machines work by digitizing an image. In effect, what they’re doing is dividing the image into a grid of dots. Each dot is either on or off, depending on whether it’s black or white. Electronically, each dot is represented by a bit that has a value of either 0 if it’s off, or 1 if it’s on. In this way, the fax machine translates a picture into a bitmap, or a series of zeros and ones that can be transmitted using the same method as computer data. On the receiving end, the fax machine reads the incoming data, translates the zeros and ones back into dots, and prints the picture.

The parts of a fax machine include an optical scanner for digitizing images on paper, a printer for printing incoming fax messages and a telephone for making the connection. Some of the older printers on fax machines are thermal, meaning they need a special kind of paper. That’s those rolls you have to put in the machine.

The first fax machines

If you examine the original fax machine invented by Alexander Bain in 1843, or the Telediagraph invented by Ernest Hummel in 1898, you can get a good idea of how they work today. As an example, we’ll look at Hummel’s Telediagraph.

This copying telegraph, as Hummel called it, used synchronized rotating 8-inch drums, with a platinum stylus as an electrode in the transmitter. The original image was drawn on an 8” x 6” piece of tinfoil, with non-conducting ink made from a mixture of shellac and alcohol. The image was received on carbon paper wrapped between two sheets of blank paper. When the electrode touched the tinfoil in the transmitter, the circuit was closed. When it touched the shellac, the circuit was open. The signal controlled a moving stylus in the receiver, making it either touch or move back from the paper. At the end of each rotation, a synchronizing signal was sent, and the styluses in both machines moved 1/56” to the left before scanning the next line.

Improvements to the fax machine

As time progressed, so did the technologies of telegraphy and photography – the two basics that make fax machines work. As they improved, so did fax machines. We’ve discovered how the first fax machines work – now let’s look at the next phase.

The process involved in the next fax machines was basically the same as the original, but with a few improvements. The next machines still used the rotating drum technology. But with the first machines, the image had to be drawn. Now, with the introduction of photography, the image could be photographed.

To send a fax, a piece of paper would be attached to the drum, with the print facing outward. A small photo sensor consisting of a lens and a light, was attached to an arm that faced the sheet of paper. The arm moved downward over the sheet of paper from one end to the other as the sheet rotated on the drum. The photo sensor focused on a very small spot, which was either black or white, on the paper. The drum rotated, allowing the photo sensor to examine one line of paper at a time.

This information was transmitted through a telephone line, using tones. If the spot of paper that the photo cell was looking at was white, a certain tone would be sent. If it was black, a different tone would be sent. These tones were actually different frequencies on the phone line – for example, 800 Hertz for white and 1,300 Hertz for black. At the receiving end, there would be a similar rotating drum, with some sort of pen to mark on the paper. When the receiving fax machine heard a 1,300-Hertz tone, it would apply the pen to the paper. When it heard an 800-Hertz tone, it would take the pen off the paper.

Modern technology is applied to fax machines

Fax machines today use the same basic technology as they always did, but with improvements that kept up with other technological advances. One of the major differences in today’s fax machines is that they don’t use the rotating drum anymore. You know you have an older machine if you have to load it with rolls of special fax paper.

Newer fax machines still use sensors to read the paper. Actually, most fax machines today have paper-feed mechanisms so you can send multi-page faxes. The black and white spots are still encoded and sent through the phone line, and there’s still a mechanism at the receiving end that marks the paper with black dots.

Today’s fax machines typically use a photo-diode sensor system, consisting of 1,728 sensors. It scans an entire line of the document at a time. The paper is illuminated by a small fluorescent tube to give the sensor a clear view. This image sensor searches for black or white and encodes the pattern of spots and sends them through the phone line. The receiving fax machine decodes the scanned lines and prints the fax.

There are a few different methods of printing the fax on the receiving end. The oldest method, mentioned earlier, is using rolls of thermal paper. Fax machines that use this paper have some significant advantages: they’re inexpensive to make; they have no moving parts, except the paper-feed mechanism; there’s no ink or ribbons (the paper contains the ink); and they’re nearly indestructible. Other methods include thermal film (which is more complicated than thermal paper, but less complicated than inkjet), inkjet and laser. Also, faxes can be received directly into a computer that has a fax modem, and printed out with whatever printer is attached to the computer.

Fax machines get the message across

So now you know how fax machines work – both back when they were first invented, and through to how they work today. If you’re one of the regular computer users of the modern age, then, along with your computer, you probably have a printer, a photocopier and a fax machine. You may even have one of the all-in-one models. Whatever you have, you can now get your messages on your fax machine because you now have “just the facts”.

About The Author

Gareth Marples is a successful freelance writer providing valuable tips and advice for consumers purchasing discount ink cartridges, and Internet optimizers online.His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.

This article on "How Fax Machines Work" reprinted with permission.

© 2004 - Net Guides Publishing, Inc.

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