II.

How Facsimile Machines Work

The standard facsimile machine works like a combination telephone and photocopier. The user places the documents into a document feeder on the sending machine, then dials the telephone number of the receiving fax machine. A gear mechanism pulls the original document over an optical scanner. The scanner records variation between light and dark areas of the document as dots arranged in a series of rows or columns. A photoelectric cell converts the dots into electronic impulses, which are then transmitted to the receiving fax machine via telephone lines.

The receiving fax machine decodes the electrical impulses into a series of dots. It sends the decoded signal to a print mechanism built into the fax machine, which prints a duplicate of the original document. International standards ensure that fax machines around the world are compatible with each other.

Older fax machines use special thermal (heat-sensitive) paper, which passes over wires that are heated in response to the electrical impulses transmitted by the sending fax machine. The thermal paper darkens when exposed to the heat of the wire to create a copy. Newer fax machines use small laser printers or ink-jet printers built into the fax machine to reproduce documents.