Is CQXT calibration NIST traceable?


Question : Is CQXT calibration NIST traceable?

Answer: Depending on the exact phrasing of the question the answer changes. Calibration of a CQXT is twofold. There is a Photometric Calibration where the instrument is flashed with no specimen or a blank specimen in the light path and the resultant measurement is scaled to represent 100% T at all reported wavelengths. NIST traceability does not apply since technically there is nothing in light path. The CQXT is subjected to a Wavelength Calibration at the factory using the emission lines from a Hg and a HeNe laser. Since these gases are constants of nature NIST considers their emissions to be unchanging. So NIST has no involvement with the photometric calibration of the sensor. The NIST Atomic Spectra Database Lines website contains a list of the known emission lines of these gases.

HunterLab uses colored glass filters to perform system validation. These filters represent the population average for a group of CQXT instruments in a known good Wavelength Calibration status. This population average has no direct comparison to NIST measurements. If a customer CQXT cannot measure the colored glass filters to within the HunterLab specified tolerances then the instrument will need to have its Wavelength Calibration reassigned.

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