Key Takeaways
This article provides details on why calibration is essential for barcode verifiers:
- Calibration helps maintain ISO compliance
- Conformance calibration cards help validate verifier performance
- Calibrating your verifier helps account for environmental changes
What is calibration, and what role do calibration cards play?
What is calibration?
Calibration is the process of mapping a camera’s measurement to actual reflectance levels, establishing a baseline for verification software reflectance levels. The calibration process adjusts reflectance levels and checks these levels to ensure the most accurate verification results. To be ISO compliant, a verifier must have a calibration process.
What is a conformance calibration card?
Conformance calibration cards are a widely used industry tool designed to support the proper calibration of verifiers. The card contains “Conformance Test Symbols” with intentional imperfections that check the reporting capabilities of the verifier and document conformance to industry standards such as ISO 15415, ISO 15416, and GS1 specifications. Since these cards can be used as a quick way to double check that the verifier is working properly, some companies have written requirements to use them in their quality processes. Certain industries also require the use of a card with conformance test symbols in their application standards.
Examples of barcode verifier calibration cards.
Does it matter what symbology is used when calibrating?
Calibration isn’t symbology specific. Once a verifier is calibrated, it can verifier 1D and 2D barcodes.
Is there a conformance test for the ISO/IEC TR 29158 (AIM DPM) grading standard?
There are no DPM specific calibration cards for the ISO/IEC TR 29158 standard. A Data Matrix conformance test card can be used, but the contrast values will never perfectly match the value on the card because of the image adjustment used in the ISO 29158 standard. The ISO 29158 grading standard can check for correct operation but will yield results that are different than those shown on the conformance card. It is recommended that the verifier also be tested using the ISO 15415 standard.
Where can the calibration result be viewed?
Check to see that the verifier is returning the correct Rmin/Rmax (sometimes labeled RL and RD) values by verifying the test symbol as you would a normal code. In the verification software for Cognex verification products, the Rmin and Rmax values are found next to the Symbol Contrast grade in the Quality Detail section of the verification software and report. These values should match those shown on the card and allow small tolerance variations.
How often do verifiers need to be calibrated?
Every company has their own policy on how often to calibrate a barcode verifier. Cognex recommends calibrating every 30 days to account for environmental changes like ambient light and temperature.
How often do calibration cards need to be replaced?
Calibration cards expire two years from the in-service date recorded by the end user. Cards should be safely stored away from dust and direct sunlight when not in use.