| Popis: |
With the use of the primary volumetric calibrator described in another paper presented at this Conference, two Venturi flowmeters of different sizes, and covering respectively the ranges 0.5 to 4 and 3.5 to 25 g/s, were tested and calibrated in cryogenic helium under several thermodynamic conditions. Designed by scaling down ISO specifications, they are equipped with commercially available ∆P meters (Validyne DP-10 type) which are placed closed to them, that is in the low temperature environment. Results are given for saturated helium at 4.2 K, superfluid, and, only for the larger meter, supercritical helium at 4.2 K and 0.4 MPa absolute. The slight differences noticed in the tests performed under different thermodynamic conditions are discussed. Under constant conditions, short-time repeatability was fairly good and never exceeding ± 0.5 %. While the zero drift of the ∆P transducers during individual tests or even when changing the thermodynamic conditions appears negligible (generally less than 0.1 %), during the cool-down between room and LHe temperature it is generally noticeable (up to 1% or more), and is probably due to mechanical settling of the diaphragm; the instrument zero therefore must be adjusted at the beginning of low temperature operation. |
