3. Accurate dosing

As with any trace analysis, the relative precision of hydrogen analysis is rather poor. It is difficult to quantify, as many factors, such as sampling quality and instrument calibration, influence the quality of results. We need to distinguish between the accuracy of the measuring equipment, the accuracy of the dosage itself (including hydrogen separation) and the accuracy obtained during production control (taking account of sampling imperfections).

The accuracy of measuring equipment is determined by repeatedly sending out given quantities of hydrogen, assumed to be perfectly determined. It is then possible to calculate a "calibration" standard deviation. With modern catharometers (thermal conductivity measurement), we can achieve extremely low coefficients of variation CV [ratio between the standard deviation of dosing (on a homogeneous sample) and the quantity...