Inconsistent Barcode Verifier
Barcode verifiers are designed to be reliable, which means accurate and repeatable. When they are not, eroded confidence creates an emergency with an uncertain path to resolution. One of the most common causes of verifier inconsistency is calibration—or lack of it. Barcode verifiers are precision measurement instruments and require regular, periodic recalibration, using a NIST-traceable test target. If this is not available, at very least a “golden” barcode of known quality can be a benchmark. If the ISO parameters are grading differently today than they were before, recalibrate the verifier and repeat the test.
A damaged verifier may malfunction. A scratched or broken scanner window can cause inconsistency, as can a dusty or dirty optical path. Examine the device and carefully clean internal mirrors and lenses. Often a blast of clean, oil-free air is sufficient.
Beware of old verifiers. Just because it still starts up does not mean it does its job accurately. The rationale that “…it is old but it is better than nothing…” is simply wishful thinking. It is not true.
If the verifier is performing properly, the barcodes you are testing may be responsible for inconsistent test results. The first place to look is average bar gain. Every barcode has a tolerance—a range of acceptable error—on bar and space width. Typically, bar gain and tolerance are a percentage of the X dimension. Acceptable gain should be in single digits. Bear in mind that gain could be a minus number.
Another cause of inconsistency is the verifier’s operating aperture. All verifiers have a range of apertures which determines how large and how small an X dimension they can accurately grade. Too small an aperture for a very large X dimension can make the verifier much fussier, seeing every tiny flaw in bars, edges and spaces. If the aperture is too large relative to the barcode’s X dimension, the verifier will be unable to accurately gauge bar and space widths, and will return varying results.
As an example, the GS1 General Specification states that UPC barcodes should be scanned (and therefore verified) with a 6 mil (0.006”) aperture. See Figure 22.214.171.124-1. Verifiers for large ITF-14 barcodes may not have a 6 mil aperture, and would therefore return inconsistent, inaccurate results on UPC symbols.
The following table from the ISO 15416 Standard provides a guideline for verifier apertures based on X dimension:
Barcode verifiers are meant to convey information about a barcode—information that helps to identify a problem that leads you to a resolution. But sometimes the information is about the verifier. Have a strategy in place to determine if the inconsistency originates with the verifier itself. Verifier consistency begins with a high quality device and a consistent schedule of care and maintenance.
Check with your reseller or with the verifier manufacturer for ISO re-certification and recalibration resources. Contact us here for assistance.
Comments and questions are always welcome.
BARCODE TEST LLC