The computer-controlled constant-temperature anemometer. Aspects of set-up, probe calibration, data acquisition and data conversion

In former times anemometers were purely analogue instruments, where the entire set-up was performed from the front panel, and data were acquired and processed in dedicated analogue computers or acquired and reduced by means of user-developed software. The modern computer-controlled anemometer is part of an integrated system consisting of the anemometer hardware, data acquisition devices, personal computers and dedicated application software. It represents an efficient alternative to the traditional manually operated anemometers as it provides automatic set-up, calibration, data acquisition and data reduction. All these operations and processes are controlled from the PC via dedicated application software packages. In order to ensure applicability to the wide range of applications appearing in fluid mechanics research the anemometer and data acquisition system must be highly flexible. This paper describes the aspects of computer-controlled anemometer set-up, calibration and data acquisition with emphasis on accuracy. It demonstrates how calibration, curve fitting, signal conditioning and digitizing influence the accuracy of measured time series and concludes that the computer-controlled constant-temperature anemometer may be considered a 1% instrument in the case of single wires, while the decomposition of X wires adds 1% more uncertainty to the cross component.