title: An absolute instrument for determination of the speed of sound in water.
abstract: An apparatus for the absolute determination of the sound speed in water based on the time-of-flight technique is described. The time measurement is realized by hardware circuits and the distance measurement by a double-beam plane-mirror interferometer. A highly accurate time chip, with a resolution of approximately 90 ps, is employed for time measurements. The acoustic path length is adjustable and can be measured directly. Two transducers are used for transmitting and receiving ultrasonic signals without reflection. The transducers are immersed in a thermostatic vessel that maintains bath temperature with high stability. The speed of sound in pure water was measured at ambient pressure and at the temperatures 308 K, 303 K, 298 K, and 293 K. The achieved measurement uncertainties are 2 mK for temperature and 0.045 m/s for speed of sound. The results are compared to data from the literature, equation of state models, and measurements by two commercial sensors in the same experiment, showing excellent agreement among them.
authors.affiliation: State Key Laboratory of Precision Measurement Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Li
authors.affiliation: Tianjin Key Laboratory for Control Theory and Applications in Complicated Systems, Tianjin University of Technology, Tianjin 300384, People's Republic of China.
authors.forename: Junchao
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Tianjin Entry-Exit Inspection Quarantine Bureau Technical Center for Safety of Industrial Products, Tianjin 300308, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Li
authors.affiliation: Tianjin Key Laboratory for Control Theory and Applications in Complicated Systems, Tianjin University of Technology, Tianjin 300384, People's Republic of China.
authors.forename: Baofeng
authors.initials: B
authors.lastname: Zhang