Model 001 & 002 Flowmeter Operating Manual
MANUAL-1550859975-1 | issue: 1.1
©
2021
– Valeport Ltd
Page | 29
Method and Result of Group Calibration
Extract from Full Report.
The minimum and maximum values of rotation speed, within which the equation should be
restricted, had now to be determined. The minimum value represents the minimum response
speed of the group of current meters, which is by definition the limit of predictable low-speed
performance. Extrapolation beyond this point would be unreliable, so it was necessary to choose a
conservatively high value of minimum response speed to allow for the individual meter which may
have a particularly high minimum response speed. For the group of 20 meters tested, the mean
value of minimum response speed was 0.046 m/s, with standard deviation of 0.0046 m/s. The
highest value measured was 0.054 m/s. Since the value of (Mean +3 x Standard Deviation), which
may be expected to include 99.8% of all meters, was 0.060 m/s and exceeds the highest
measured value, a minimum response speed of 0.060 m/s was accepted. From the relevant
equation this flow speed corresponds to a rotation speed of 0.26 m/s.
All the meters except three were run to a maximum speed of about 3m/s, the exact value varying
from test to test. However, the choice of an upper limit for the group calibration is less critical than
the lower limit, as a well-designed meter has an extended near-linear performance at higher
speeds. Earlier work with a Braystoke meter showed that if a flow speed at 4.9 m/s was computed
from a rating equation whose upper limit was 2.8 m/s, the result was only 1.1% in error. Hence, the
upper limit of flow speed adopted was chosen, by inspection, to include 95% of the measured
values below it. This limiting value was 3.023 m/s, corresponding to a rotation speed of 27.86 m/s.
In view of the above comments the HRS calibration tables have been extended to include all
values of rotation speeds, from 0.12 to 46.32 corresponding to a range of flow speeds from 0.046
to 5.000 m/s
Acknowledgements
The above summary, report extract and following calibration tables are reproduced from HRS
Report No. DE57 (Calibration B2/2), June 1982 with the kind permission of Hydraulics Research
Station, Wallingford, England. For a full detailed description of the group calibration, please refer to
this report.