An auto document feeder is a very handy feature on a scanner if you scan multiple documents at a time very often. An auto document feeder is an electromechanical device that accepts a stack of documents in its tray and feeds them to the scanner one at a time. It then waits for the scanner to scan the document before feeding a new document to the scanner. A scanner equipped with an auto document feeder can save you hours of tedium waiting for one sheet to be scanned, opening a flatbed scanner's lid, removing the finished document, positioning a new document, closing the lid, and waiting some more.
An auto document feeder's most important features are its capacity and its speed. The greater both are, the more a scanner with an auto document feeder will cost. Consider your speed and capacity needs and buy a scanner with an auto document feeder that matches your needs closely.
An auto document feeder's speed is measured in the number of pages it can feed per minute (ppm or pages per minute). It is important to note that almost any auto document feeder's speed is faster than the speed at which a scanner can scan a single page. That is, the auto document feeder does not limit the scanner's performance. But the faster an auto document feeder feeds a page to a scanner the less time the scanner spends waiting for a new document, and the overall processing will go that much faster. When a scanner's specs say, "so many ppm" it usually refers to the total time needed to feed and scan a page.
A scanner equipped with an auto document feeder should also have a flatbed or single-sheet feeder. An auto document feeder has many moving parts and therefore is more prone to mechanical failure more often than the digital parts of a scanner. If the auto document feeder on your scanner breaks down, you should still be able to feed the scanner one sheet at a time, however tedious that may be. It's a good idea to download a scanner's user manual from the vendor's Web site and see how good the auto document feeder troubleshooting section is before you buy.
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