The ONH836 Oxygen/Nitrogen/Hydrogen system is designed for simultaneous wide-range measurement of oxygen, nitrogen, and hydrogen content of steel, refractory metals, and other inorganic materials. The instrument features custom software designed specifically for touch operation.

A pre-weighed sample is placed in a graphite crucible which is heated in an impulse furnace to release analyte gases. Oxygen present in the sample reacts with the graphite crucible to form CO and CO₂. An inert gas carrier, typically helium, sweeps the liberated analyte gases out of the furnace, through a Mass Flow Controller, and through a series of detectors. CO and CO₂ are detected using non-dispersive infrared (NDIR) cells. The gas then flows through a heated reagent where the CO is oxidized to form CO₂, and H₂ is oxidized to form H₂O. The gas continues through another set of NDIR cells where H₂O and CO₂ are detected. The CO₂ and H₂O are then scrubbed out of the carrier gas stream, leaving the final analyte, nitrogen, as the only impurity.

A patented Dynamic Flow Compensation (DFC) system is used to add carrier gas as a makeup for the gas lost during the scrubbing process. A Thermal Conductivity (TC) detector is used to detect nitrogen. The detection system is comprised of both NDIR and TC detectors. NDIR cells are based on the principle that analyte gas molecules absorb infrared (IR) energy at unique wavelengths within the IR spectrum. Incident IR energy at these wavelengths is absorbed as the gases pass through the IR absorption cells. The complete set of CO and CO₂ NDIR cells is required to give the most accurate oxygen results for a wide range of sample types and concentrations. TC detection takes advantage of the difference in thermal conductivity between carrier and analyte gases. Resistive TC filaments are placed in a flowing stream of carrier gas and heated by a bridge circuit. As analyte gas is introduced into the carrier stream, the rate at which heat transfers from the filaments will change producing a measurable deflection in the bridge circuit.

The concentration of an unknown sample is determined relative to calibration standards. To reduce interferences from instrument drift, reference measurements of pure carrier gas are made prior to each analysis.