Troubleshooting

 

Troubleshooting is basically a controlled process of elimination where only one variable is checked at a time. It is necessary to systematically test each part of a system or process to determine the cause of a problem. It is crucial to eliminate only one variable or it is not possible to figure out which variable caused the problem.

Troubleshooting a bad bar code symbol and/or label:

• Visually inspect the label for damage, dirt, tears, and ink marks. If any of these defects exists,  reprint the label and verify (to verify a bar code symbol, you will need to purchase a device called a verifier designed specifically to analyze a bar code) or scan it.

• Look for quiet zones at each end of the bar code. For Code 39, there should be approximately 0.25 inch of white space at the beginning and end of the bar code. If this space is not available you must change the parameters of the bar code or increase the width of the label stock. For UPC/EAN symbols, there should be approximately 0.15 inches at both sides of the symbol. For two-dimensional symbols, you will need to check the specification for the symbology. Depending on the 2D symbol, there can be as little as 0.010 inch of white space around all edges of the symbol. (Top, bottom, left, and right.)
• If the label passes a visual inspection, validate that the scanner you are using is a visible laser diode scanner. If you are using an infrared scanner along with direct thermal labels, then make sure you are using direct thermal label stock  that is designed to work with an infrared scanner.
• If the label passes a visual inspection, validate that the scanner you are using is working by trying to read another label. If your scanner does not read the other label, then read either label with another scanner. See the section below to troubleshoot a scanner.
• If the label passes a visual inspection, and if neither scanner reads the label, make sure the scanner/decoder you are using is set for the symbology used to encode the bar code.
• Assuming that you still cannot read the bar code on the label, you should now use a verifier to determine what is wrong with the bar code. First, make sure your verifier is calibrated. If the verifier cannot decode the bar code, check the printer for printhead defects, motor speed variations, label stock feed, toner, ribbon and its settings for heat. Remember to check each problem individually and validate its performance before going on to the next item.
• If you have not yet solved the problem with the label, it is possible that the software printing the bar code has not encoded the bar code correctly. This may happen if you are using a new software package or if your encoding program was written in-house. Missing start and stop characters are a common problem.

• If the verifier decodes the bar code, it will identify the parameters that are causing the problem. Once you know which parameters have failed, you need to correct the problem(s). Occasionally, the bar code is so bad that a verifier can not decode the symbol. In most cases the verifier can still identify the problem(s).
• The verifier will report on the following parameters: Contrast, modulation, and decodability. These parameters are related to bar and space reflectance (how black the bars are and how white the spaces are to the scanner) and can be improved by checking the following:
  • For thermal printers – burn time and heat settings, printing (feed) speed, label stock per manufacturer requirements, thermal transfer ribbon per manufacturer requirements.
  • For laser printers – Toner, density setting, selected x-dimension not less than .010 inch, label stock.
  • For dot matrix printers – Ribbon, print head/ribbon spacing (adjustable) needs to be set for the thickness of the label stock (for multi-part forms, the bar codes are expected to read on the original only, not the copies).

Troubleshooting a scanner:

• If you are unable to read a bar code with your scanner first make sure that the bar code you are trying to read passes the verification process. If the bar code does not pass see the section on troubleshooting a bar code symbol.
• If your scanner is attached to a decoder with a cable, first plug a different scanner into the decoder and try to scan the symbol. If the cable can be disconnected from both the scanner and the decoder, use the same cable so that the scanner is the only variable you are testing. If the second scanner is able to decode the symbol, then the first scanner will need to be sent to the manufacturer for repairs. If neither scanner can decode the symbol, change the cable and test again. If you still can not read the symbol,   then go to the next step to set up the decoder correctly.
• If you are using a scanning terminal, an integrated scanner/decoder, or you failed the two previous steps, find your user manual for the scanner and make sure that the scanner is set to the parameters that you need for your application.  Depending on the manufacturer of your scanner, you may need to set dip switches or scan bar codes in the user manual to correctly set up the scanner.  Check the following:
  • Make sure the scanner/decoder you are using is set for the symbology used to encode the bar code.
  • Make sure the communications interface with the host system is set correctly.
  • Make sure that the optical specifications for the scanner agree with the type of bar code you are trying to read.