Verifier silence can be even more confounding than decodability and modulation. Relating these rather exotic parameters to the print process and using them to decide what to do is sometimes unclear but at least you have a successful scan. What does it mean when you don’t? What about verifier silence?.
What about those times when the verifier tells you nothing—silence. What does it mean when the verifier produces no decode, no grade?
Verifier silence. What Does It mean?
Verifier silence is significant. But what does it mean?
A verifier is an aggressive decoder. It has to be because it can’t grade a symbol if it can’t decode it.
When the verifier only decodes one in ten attempts—or none at all—is meaningful. The challenge is to figure out verifier silence in nine of ten scans.
The first thing to do is examine the barcode with a low power magnifier—I prefer 8X. Examine the narrow elements (bars and spaces). These are the building blocks of every linear symbol. Most (but not all) linear symbols have only two element values: wide and narrow. UPC and Code 128 have more than two, but don’t let that discourage you. Look at the narrow bars—you should see that there are many of them across the symbol. Visually note how wide the narrow bar is—then look at the narrow spaces. If they are not very similar in width to the narrow bar, this could be the source of your decode problem.
When the narrow bars are obviously wider than the narrow spaces, this is usually caused by press gain. The wider-than-nominal bars are encroaching on the spaces, robbing them not only of real estate but also of reflectivity. Maybe the verifier silence is due to excesive press gain.
Next, using your magnifier, notice if there are defects in the symbol: voids in the bars and/or spots in the spaces: these can really confuse a verifier. To a scanner, a major void in a bar can look like two narrow bars with a narrow space between them; a spot in a space can look like an extra bar. Maybe the verifier silence is because of defects that throw off the correct bar and space count in a symbol.
Now, examine the edges of the bars. Are they uneven or ragged? Are they different on the left side than on the right side? Are the bars wavy or jagged from the top of the symbol to the bottom? Is the verifier silence limited to a particular area in the symbol?
Finally, notice if the bars are dark and opaque and the spaces bright and clean: there should be no show-through of the background through the bars. Neither bars nor spaces should ever be screened. Ideally the bars should be black against a white background but if the barcode is printed in a color, the bars should never be a red or red-containing color. Green is usually OK for bars. Likewise the background is ideally white but should never be green or green-containing. Red is usually OK for the background. Perhaps the verifer silence is because it can’t see the symbol.
Correct these problems and rescan the symbol. Your decode rate should improve enough to show you what ANSI parameter is (or parameters are) controlling the final grade.
Verifier decode can cause confusion
Verifier decode aggressiveness can cause confusion. When the symbol is decoding but the final symbol grade is consistently an F, what should you believe?
You should believe the symbol grade. Because a decode was achieved, the verification report will tell you which parameter(s) contributed to the failing grade, so finding a solution is much easier than when there is no decode.
Verifier decode of a symbol—even consistently—is less significant than the final symbol grade.
If all of these attempts fail, send an actual sample of the symbol to an outside test lab for evaluation.
Pay attention to verifier silence and believe the verifier grade
Finally, attention when your verifier speaks in extremes—first a B, then an F, then an A, then a D. This is also significant but sometimes difficult to pin down. Use a disciplined test procedure: take a series of verification scans of the symbol from the top to the bottom.
Is there a difference in symbol quality from top to bottom?
The key to solving most barcode quality issues is not to reply too heavily on the technology. Use your eyes.
When necessary, seek reputable help such as Barcode-Test LLC.