The mercury concentration is measured in an optical cell entirely made of a high purity grade fused silica. A maintenance-free membrane pump continuously feeds the sample gas to the optical cell where light absorption measurement takes place at a wavelength of 253.7 nm. This so-called "cold vapor" measuring method is extremely sensitive for mercury determination and has been used successfully for many years.

The Mercury Tracker 3000 uses a high-frequency driven electrodeless Hg low pressure (EDL) lamp as UV source. It generates emission lines of an extremely narrow bandwidth which are congruent with the absorption lines of the Hg atoms. Cross-sensitivities are thus minimized. Unlike the gold film based systems measurements are not interfered by H2S. The extremely high stability of the UV source is a result of the reference beam method which is applied in the Mercury Tracker 3000. Total background noise is less than 0.1 µg/m3. To prevent temperature drift both the lamp unit and the detectors are temperature-stabilized. The instrument is calibrated before delivery and keeps the calibration for a long period of time. For quality control a test screen is included in the delivery allowing the user to check calibration.