Comparison of different methods for the determination of dynamic characteristics of low velocity thermal anemometers

摘要

Three methods for determining the dynamic characteristics of low velocity thermal anemometers were compared. They were: step-up velocity change and step-down velocity change methods and a method based on sinusoidal-type velocity fluctuations. Two low velocity thermal anemometers with omnidirectional velocity sensors were tested. The results identify differences in the frequency response of low velocity anemometers determined by the three methods. The time constant and the response time determined by the step-up velocity change method and the step-down velocity change method may be substantially different and insufficient for describing the frequency response of all low velocity thermal anemometers. Therefore the upper frequency, determined in tests with sinusoidal velocity fluctuations, is recommended to be used in indoor climate standards as a single parameter describing the dynamic characteristics of low velocity thermal anemometers. A method for improvement of the frequency response of low velocity anemometers is suggested and validated.