Method and apparatus for determining diffusible hydrogen concentrations

A measuring apparatus and method for use in measuring diffusible hydrogen concentrations in materials, structures, and other objects. In an embodiment of the invention for use in welding applications, the measuring apparatus includes a sensor assembly that, with an included sealing member, defines a sample area on a weld bead from which hydrogen evolves into a sample volume defined by the sealing member, a sensor housing and a sensor of the sensor assembly. The hydrogen reacts with a sensing layer and a reflector layer positioned on the end of an optical fiber, all of which are included in the sensor assembly and are sealably positioned within the sensor. The sensing layer comprises a chemochromic material that undergoes changes in physical properties, such as optical transmission properties, when it reacts with hydrogen and these changes are measured by the measuring apparatus to determine the amount of hydrogen evolving from the sample area. An optical fiber is joined to the sensor optical fiber to direct light transmitted by a light source in a hydrogen monitoring assembly through the sensing layer to strike the reflector layer which reflects light back through optical fiber to a detector in the hydrogen monitoring assembly. A signal analyzer is included in the hydrogen monitoring assembly and is calibrated and configured to measure the diffusible hydrogen concentration in the weld bead based on measured changes in the optical transmission properties of the sensing layer.