Good question. To answer this good question, we need to ask more good questions. Here are a few good questions to start with:
What is the reading distance of the item to be scanned?
For average size codes, linear imagers and laser scanners work exceptionally well at a standard scanning range of up to 18 inches (46cm). Area imagers can capture codes up to 9 inches (23 cm) in range. If the labels are more than 18 inches away, long-range laser scanners are the only option. However, lower resolution (larger) codes allow longer read ranges than high-resolution (smaller) codes across all technologies.
The read distance of RFID tags depends on the frequency of the tag. For example, a 915 MHz tag has a typical read range of 10-13 feet, whereas a 2450 MHz tag can be read from up to 48 inches.
What type of symbologies will be used?
Most scanning technologies read the same common set of linear bar-code symbologies in a variety of bar-code densities (i.e. the number of characters which can be represented in a linear unit of measure), including EAN/UPC, Code 39, and Code 128. Linear imagers are the best choice on these codes at higher code densities (where more characters are packed into the same space), in the region of X-dimensions (narrow bar width) between 2 mil and 5 mil (0.05 and .1mm), and with code widths up to 8 inches (200 mm) for X-dimensions between 10 and 20 mil (0.25 mm and 0.5mm). For applications where scanning matrix codes or a wide variety of symbologies is necessary, area imagers are the best option.
Are you required to produce compliance labels?
Some major retailers and the Department of Defense are requiring their suppliers to incorporate RFID tags into their outbound shipment labeling. Fixed RFID readers and RFID handheld devices for exceptions management are the best answer in this application. Other compliance-labeling requirements may dictate that matrix codes be incorporated into a label with linear codes and human-readable information, in which case area imagers are ideal.
Do you need non-line-of-sight scanning?
Because RFID is the only radio-based data capture technology, it does not require an optical read of the tag. RFID readers can also read dozens of tags simultaneously, making them ideal for tracking large quantities of goods through warehouses and distribution centers.
What is the condition or source of the bar code?
Poor quality codes or codes that must be read through laminates can be very difficult to read. Linear imagers are not only excellent at higher densities, they also read poor quality codes and codes with low contrast between bars and spaces (caused by the color or poor printing/fading) exceptionally well. Some linear imagers can also cope well with damaged codes. The faster scan rate of linear-imaging engines plays a significant role in these capabilities, as do the methods used to decode the complex video signal information provided by the linear imager.
What are the environmental conditions?
The working environment will certainly dictate how rugged the scanner needs to be, but even a seemingly “safe” environment like retail can prove a tough environment for scanners with moving parts, which can get jarred out of alignment by rough handling. Linear and area imagers (as well as RFID readers) are solid state without any moving parts. Because of that, they tend to be more reliable than lasers, which use moving mirrors to make the laser spot travel across the code. However, ultimately it’s the casing of the scanner that dictates its suitability for certain environments. In retail, for example, a linear imager in a standard ABS plastic case will provide a durable, long-life solution, whereas a more rugged casing would be needed for the same scanner in a warehouse or industrial application.
Do you need to read bar codes off computer screens?
One unique application for linear imagers is reading bar codes off computer screens. This is extremely helpful in configuring devices via bar codes, especially if you have a large number of devices to configure. Instead of printing out a series of bar codes, you simply display them on a computer monitor and scan them directly.
How important is performance?
If a scanner reads a code, then regardless of its technology, the performance differences between it and another will be judged on issues like speed of reading, scan range and definition of reading zone. Within their scan range, linear and area imagers can provide exceptional performance. Some linear imagers are contact readers and will only read if the scanner’s nose is touching the code. This is appropriate for flat surfaces, but can cause problems if the code is on a curved surface. Long-range linear imagers are better for curved surface scans. Standard-range linear imagers can read up to 18 inches (46 cm).
As the reading distance increases, it becomes more important to know where the scan line is. With laser scanners this is clearly marked by the laser line. Linear imagers depend on the illumination of the bar code by the LEDs, so the scan line may be more difficult to see as the reading distance increases or in high ambient light conditions such as direct sunlight.
How much do I want to pay?
Linear imagers are generally less expensive than lasers, area imagers, and RFID readers. Normally, the improved productivity more than pays for the equipment.