There is an increasing demand for velocity calibrationsin the range of 0.05 up to 5 m/s with the respect to thermal anemometers. These meters are used for e.g. human confort measurements (draught in workshops and offices), air-conditioning and clean room test procedures. Tha advantage of using thermal anemometers is : small dimensions, hardly and blockage effects of the duct and a negligible hysteresis in comparison with the mechanical meter. Drawbacks : the reading may be effected due to the variations in air density, temperature and non-axial velocities generated by specific test facility (degree of turbulence).
An extension of Project 388 is proposed while:
- an intercomparison project 388, windmill type anemometers were used. Because of the machanical resistance, velocity calibrations lower than approximatively 0.4 m/s coult not be compared using small anemometers
- Differences in degrees of turbulence can be evaluated using the results of the thermal and the additional mechanical anemometer
Aim od the proposal :
- intercomparison of anemometer test facilities at very low velocities
- Evaluation of consistency with the lately finished 388 project at overlapping intermediate velocities, deviations in results demonstrate degree of turbulence when the flow profiles are reproductible to projt 388
Use transfer meters :
One thermal probe a,d a similar spare probe, electronic display with density compensation circuit, digital and analogue readout (type : Lambrecht 642)
One mechanical anemometer (type : probably "mimiair60/macro, Schiltknecht" as used in project 388)
Range of interest : 0.05 m/s up to 5 m/s
- damage of probes during transportation and/or handling, instability of electronic circuits
- sensitivity related to air temperature variations of the different test facilities may be too high for getting reliable results
The transfer equipement will be sent to the participating laboratories by parcel expedition, starting and ending at NMi-VSL. Eventually, extra intermediate test may be executed at NMi-VSL
Final Report 2008-02-28
The comparison has been completed and results are published in the KCDB.