A Comparison of Climatic Chamber Hygrothermal Characterization Techniques as Described in IEC60068

Abstract

Techniques for the evaluation of the spatial temperature and humidity performance criteria of climatic chambers are described within the various sections of the International Electrotechnical Commission (IEC) Standard IEC60068 applicable to environmental testing. This paper involves the comparison of three common measurement systems used to assess the performance of climatic chambers, as well as the development of methods for determination of uncertainty contributions, and subsequent propagation into an uncertainty analysis for each method. Methods for validating the performance of these chambers should include specific uncertainty contributions, such as fluctuations, homogeneity, radiation, sampling, and loading effects. These effects are discussed and evaluated as part of this work. The procedure, as detailed in IEC60068, was followed using a chilled-mirror dew-point hygrometer with nine platinum resistance thermometers, nine calibrated RH (relative humidity) and temperature probes, and nine calibrated RH and temperature wireless data logger modules. Loading effect and dew-point uniformity were evaluated empirically and the results discussed. A summary of the results obtained and the associated uncertainty calculations are described and compared. All three systems have their merits, and lower uncertainties in both temperature and %rh were obtained for the chilled-mirror system. Loading effect:The difference in temperature at any one point due to the presence of a load in the chamber space Radiation effect:Differences in the measured temperature due to the absorption or emission of different levels of thermal radiation by the temperature sensors Dew-point uniformity: The amount of variation in the dew-point temperature within the test space, equivalent to water vapor-pressure uniformity Gradient:Maximum difference in mean value, after stabilization at any moment in time between two separate points in the working space. Fluctuation:Change (from the mean) in temperature or humidity after stabilization from time to time at a point in space.