Views: 0 Author: Site Editor Publish Time: 06-05-2022 Origin: Site
Light pen is the first hand-held contact bar code reader, and it is also the most economical bar code reader.
When in use, the operator needs to touch the light pen to the surface of the bar code and send out a small light spot through the lens of the light pen. When the light spot crosses the bar code from left to right, the light will be reflected in the "empty" part and absorbed in the "bar" part. Therefore, a changing voltage will be generated inside the light pen, which will be used for decoding after amplification and shaping.
Contact with the bar code to read, which bar code can be clearly read; The length of reading bar code can be unlimited; Compared with other readers, the cost is lower; There are no moving parts inside, which is relatively solid; Small size and light weight. For example, the light pen is not suitable for reading in various occasions; In addition, the light pen can play its role only when reading the bar code with specified density and good printing quality on a relatively flat surface; Moreover, operators need some training to use it, such as reading speed, reading angle and improper pressure will affect its reading performance; Finally, because it must be read in contact, when the bar code is damaged due to improper storage, or there is a protective film on it, the light pen cannot be used; The first reading success rate of light pen is low and the bit error rate is high.
CCD is an electronic coupling device, which is more suitable for close and contact reading. Its price is not as expensive as laser reader, and there are no moving parts inside.
The CCD reader uses one or more LEDs, and the light emitted can cover the whole bar code. The image of the bar code is transmitted to a row of light and sampled by each individual photodiode. The adjacent detection results are "black" or "white" to distinguish each bar or space, so as to determine the character of the bar code. In other words, the CCD reader does not pay attention to reading each "bar" or "space", but the whole part of the bar code, And converted into electrical signals that can be decoded.
Advantages: compared with other readers, CCD reader is cheaper, but it also has wide density of reading bar code and is easy to use. It is lighter than a laser reader, and unlike a light pen, it can only touch and read.
Disadvantages: the limitation of CCD reader lies in its reading depth of field and reading width. It will be difficult to read the bar code printed on the arc surface (such as beverage cans); It is not very suitable for some occasions that need long-distance reading, such as the field of warehouse; The anti falling performance of CCD is poor, so the failure rate is high; When the bar code to be read is relatively wide, CCD is not a good choice. The bar code with long information or low density is easy to exceed the reading range of the scanning head, resulting in unreadable bar code; Moreover, in some bar code readers with multiple LEDs, any led failure will lead to failure to read; Most CCD readers have low first reading success rate and high bit error probability.