DynH(2)O: Setup for the metrological characterization of the dynamic properties of hygrometers

A novel flow switching setup for the dynamic generation and metrological detection of fast, isolated H2O concentration changes is presented and characterized. Based on this flow setup, very accurate, static H2O concentrations as well as highly dynamic H2O step changes of several 1000 ppmv (mu mol/mol) can be generated and repeated. First experiments show that temporal water vapor concentration gradients of up to 10000 ppmv/s can be generated and measured. Based on this setup, a dynamic hygrometer characterization method was developed and demonstrated using a polymer-based hygrometer as device under test (DUT). The polymer hygrometer (with about 180 ppmv/s) proved to be more than 15 times slower than the optical reference hygrometer (with 3000 ppmv/s) and could be modeled and described well with a first order lowpass. To estimate the dynamics of the spatial and temporal H2O-profile, a fast, traversable, local sampling probe was developed and used in combination with a fast, extractive laser hygrometer (called SEALDH-II). The modeling of the H2O distribution in the dynamically operated flow channel enables the calculation of the dynamic concentration at the position of the DUT based on the data of the spatially averaging open-path laser reference hygrometer. In the future, this calculation will be used to determine a transfer function between the optical, open path reference hygrometer and the position of the DUT in order to extract the ideal step response of the DUT from the measured data of the flow channel.