Test Bar Codes: How to Do It
We have talked in the past about why you would want to test a bar code—read more about that here.
This article is all about the nuts and bolts of how to test a bar code.
To begin with, you must test a bar code with a test instrument called a verifier. You cannot test a bar code with a scanner because scanners of different brand and model behave differently. One scanner may read a bar code, another may not. With a scanner you cannot predict when or why a bar code will fail to scan.
Because a verifier is a test instrument, its results should be based on the ANSI/ISO specification for bar code quality. Some verifiers claim to evaluate bar codes based on the ANSI/ISO specification but that’s not good enough. That’s like selling somebody a ruler and promising that the increments are based on inches and feet. That doesn’t speak to their accuracy—whether the reported inch is really an inch. Sometimes you have to read the verifier data sheet carefully to be sure, but it should say “ANSI/ISO compliant” in plain language. If the language seems a bit “clever”, the device is probably not compliant and you should look elsewhere.
The ANSI/ISO specification dictates what attributes of the bar code must be tested and graded. For linear bar codes such as UPC there are nine essential attributes or parameters. Each one is tested and graded individually, and the lowest grade for any one parameter is the final symbol grade.
The ANSI/ISO parameters for linear bar codes are:
- Edge Determination
- Minimum Reflectance
- Symbol Contrast
- Edge Contrast
- Modulation
- Defects
- Decode
- Decodability
- Quiet Zones
We’ve covered these in great detail previously—read more about that here.
The ANSI/ISO specification also requires that the final grade be the average of ten scans covering the entire height of the symbol.
Regardless of the type of verifier you have, it is important to pay close attention to the process and procedure to test bar codes. Center the verifier on the test bar codes. Make sure it is carefully aligned square to the symbol. Make sure it is at the proper angle. Shield the test bar codes against ambient light that could influence the test results. Hold the verifier motionless. Make sure the verifier is set for ten scan averaging, and take ten scans through the entire height of the symbol.
The verification report is only the beginning when you test bar codes—interpreting the results in order to figure out how to improve your bar codes is the real challenge. Read more about that here.
It is not difficult to test bar codes, but it does take some care. Your experiences or questions are always invited in the comments section.
