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This paper deals with the problem of the characterization of sensors developed estimating the ice fraction in ice slurry fluids flowing into the pipes of industrial refrigeration apparatus based on secondary refrigerants. Such measurements must be performed in a non invasive way and the sensors must face with severe environmental conditions. Different sensors have been developed to this aim, that exploit various sensing principles. An optical sensor is based on a non electrical approach and relates the transmission of a signal to the ice density. While a capacitive sensor and a potentiometric sensor exploit the effects of ice particles concentration on the ice slurry fluid permittivity and conductivity respectively. In order to perform the characterization of the sensors developed, reproducible working conditions must be ensured by monitoring and controlling the main process parameters of the refrigeration apparatus. In fact, this paper presents a distributed monitoring system, that make use of STF513 microcontrollers and 12C bits, based on a LabView interface that allows to perform extensive experiments in a reproducible manner. In this way a reference realization of the quantity to be measured has been performed. A quick view of the sensors developed will be also given. A large ensemble of experimental results has been collected, by using the apparatus realized, that allows to qualify the performances of the sensors developed.