# Instrumental Uncertainty of Conductance Transducers for
## 1 Introduction  
For several decades, conductance transducers have been developed and applied by LNEC to maritime reduced-scale models, in order to obtain the measurement of a wave level and its variation under a dynamic regime, namely using infrastructures able to generate waves in hydraulic experimental facilities. Coastal engineering is a branch of civil engineering with a large impact in economic development, contributing for many types of studies, namely wave mechanics, shoreline erosion, and methods to protect the shore from extreme events (e.g., climatic, geological), and harbor design, among others. Studies often combine field observation with laboratory modeling observation and mathematical and computational calculus [1]. Laboratory studies are usually related with physical models, aiming to reproduce, at a certain scale, a physical system often providing information to the development of numerical models for hydrodynamic phenomena, leading to a modern perspective of \"Hybrid Modeling\" that combines the contributions of physical models through boundary conditions with complex interaction models of fluid flow regimes. This approach was recently named \"Composite Modeling\", being a methodology that balances the use of physical and numerical models [2]. The use of physical modeling is applied in many different domains of hydraulic engineering [3], making use of many types of models and planning approaches, in order to obtain advantages that physical models still provide [3]. Coastal and nearshore hydrodynamics are included in this context where measurement in physical models are used to analyze the travel of waves from deep waters to shallower regions, and the related effects of energy transfer and turbulence, creating complex non-linear interactions [4]. For these types of studies, laboratory experiments play a relevant role in research and development [5]. The experimental approach with physical models has been used with relevant results to provide information for decision-making processes regarding problems of coastal erosion by studying the impact of coastal structures (e.g., breakwaters, seawalls, dikes,and revetments) intended to reduce wave energy, sediment transport, and other effects of hydrodynamic nature [6]. The same applies to the development of harbors and maritime structures, regarding the analysis of complex processes of wave propagation and its interaction with coastal structures. In a laboratory, the development of experimental testing using wave generation in order to evaluate its behavior in time and frequency domains requires the use of measurement instruments that re able to obtain accurate observations within a time response suitable for the phenomena requirements. The metrological characterization and traceability of measurement instruments play a critical role in the laboratory-based research, providing the quality of measurement that is useful in the analysis of hydraulic processes, but also robust raw data for numerical model parameterization and for its validation [7,8]. This study proposes several metrological characterization methods applied to conductance transducers, integrated in SI traceability chains, and allows the determination of measurement uncertainty components, which contribute for the wave level instrumental measurement uncertainty. Due to the nature of the conductance transducer measurement principle and method, metrological characteristics, such as electrical stability, linearity, reversibility, repeatability, and thermal influence, should be known and used to evaluate if the applied transducer complies with instrumental requirements defined for the experimental observation scenario, in addition to quality production control procedures. A more robust instrumental comparison with other available measurement transducers can also be performed, contributing for the improvement of the experimental design.