Axicon the barcode experts


Verifier calibration

How calibration cards work

All barcode verifiers measure the same parameters of each barcode, and they must conform to the ISO/IEC standards for verifiers if the results from one manufacturer’s equipment are to be compared with those from a different manufacturer.  This means that each verifier must measure the reflectance from each barcode consistently, and use accurate measurements.


These standard  measurements are provided by calibration cards which are themselves measured against reflectance standards produced by the USA’s National Institute for Standards and Technology. The calibration cards supplied by Axicon are produced in the USA by a company called Applied Image which has worked with the American National Standards Institute (ANSI) and the Uniform Code Council, now GS1, since 1989 on the development of these reflectance standards.


The materials used to create calibration cards are chosen to be as colour-stable as possible, at a reasonable cost, but over time the white background will change colour. We expect the accuracy of these cards to remain stable for a limited time, provided they are kept away from direct sunlight, heat, and damp, and we recommend that users obtain a new calibration card every year to be sure that the values are correct.


The cards still need to be kept at a normal room temperature, and in the dark when they are not being used.  Keeping them inside the original wallet or envelope, inside the verifier’s case or a desk drawer, would be fine.


You must always use the original card, as it was supplied, to calibrate your verifier regularly.  Do not use a photocopy of it, or cover it with any protective film or cover, as this would affect how it works.


If you happen to have some older, unused calibration cards, you could check them against the results from a new card to see if they are still providing accurate enough readings for your calibrations, but we cannot guarantee any aspect of their performance.


Why verifiers need to be calibrated

The verifier uses the power supplied through its USB connection to light up the LEDs that illuminate the barcode, and their brightness is affected by the slight variance in the USB power between computers, and their temperature.  Brighter LEDs will mean a higher reading for the maximum reflectance – the whiteness of the calibration card – and the verifier must be calibrated to take this into account.


The verifier needs to be calibrated for each computer it is connected to, and the calibration record will be stored on each computer. The temperature in which the verifier is used will also affect the readings it takes, so if it is moved from a warm office to a cool warehouse, it should be calibrated again when it has stabilized to the new ambient temperature.


The other change that happens over time is the dimming in brightness of the LEDs. This is almost unnoticeable, but the dimmer LEDs will mean a lower reflectance reading. Calibrating the verifier also corrects for this. Apart from calibration, which needs to be carried out on a regular basis, verifiers need to have a VCAS, a verifier conformance and alignment service, every year to ensure they are still operating correctly.


Why verifiers need servicing

When we design and manufacture verifiers we aim to build them using the best components available, and we are confident that they are amongst the most robust and reliable verifiers available. They are still portable, optical devices, with components that can be affected by the environment in which they are used, and how they are handled. Over time, the LEDs may not illuminate the field of view as evenly as when they were new, and the optical components (the lens, the mirror, the filter) can be affected by tiny dust particles.


To be able to guarantee that the verifier is working as we intended, and still conforms to the ISO/IEC standards, we recommend that it is sent back to us every year for a verifier conformance and alignment service or VCAS.  The verifier will still be working within the tolerances allowed but we will check that it is dust-free, optically clean, correctly focussed, and is able to be calibrated by the user. We will also replace any components that are showing signs of wearing out, or behaving inconsistently, and ensure that the verifier works as well as it did when it was new.


How VCAS relates to the warranty period

We are confident in the design and manufacture of our verifiers, so we provide a two-year warranty against the verifier breaking down during normal use. If anything goes wrong with a verifier during its first two years, any repairs will be carried out free of charge.


The VCAS is not repairing the verifier, but ensuring that it will continue to work correctly, and be able to grade different barcodes accurately. We do not expect any of our verifiers to stop working, but the slightly changing performance of its components, as they age, needs to be checked and compensated for where necessary. If a verifier never breaks down, and is never returned for VCAS, we cannot be sure that it is grading borderline barcodes correctly, and that its readings for all the different ISO/IEC defined parameters are accurate.


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