It is our policy to  expand and communicate know-how.  An example is the drafting of ISO TS 25377: members of the Company participated on the international committee.

This Standard titled 'Hydrometric Uncertainty Guidance' provides an understanding of the nature of measurement uncertainty and its significance for defining the quality of a hydrometric measurement.

It is applicable to flow measurements in natural and man-made channels, the management of water resources and the measurement of industrial flows.

Activities such as international standards have benefited from Hymetrics' research expertise, notably where ISO 25377 has been applied to our calibration methods and to our smart-sensor technologies.

The Hymetrics calibration rig was commissioned for the development of a new hydrometric structure: the V-Flume.  A requirement of the rig was to extend scope of calibration to enable the flume to be installed in channels with imperfect hydraulics: i.e. with higher levels of turbulence or asymmetric velocity profiles as might be found in short lengths of channel.

The V-Flume, which was developed principally for industrial application, needed to be calibrated using the standard

industrial method of level measurement, namely pulse-echo ultrasonics [rather than the method advocated in the ISO Standards: the hook gauge].

A highly automated facility, capable of generating more than 10 flow characteristics per day was designed. Each characteristic has up to 16 Q-h-u(Cd) points, with each point derived from 50 individual measurements of Q and h.

To compute uncertainty values requires additional discharge coefficient uncertainty data for each Q and h value, while including sensor elevation uncertainty and sonic velocity uncertainty.

The graph shows the range of scatter of head computations that arise from surface waves, and how the sensor's vertical position and the sonic velocity contribute to the total effective head uncertainty. 

This scatter is projected into the graph on the right and combined with the uncertainties of the discharge coefficient to determine the resultant scatter of flow values.

The uncertainty of the flow measurement is equal to the standard deviation of the scatter of flow values.

To simplify and reduce installation costs, the V-Flume can be installed in shorter channels with higher levels of approach turbulence. Note: the Standards require that water approaching a flume to have low levels of turbulence.  For this reason the Standards specify long parallel-sided channels. 

A series of tests were conducted to see how sensitive the V-flume is to channel turbulence.  It was found that these effects are not as significant as had been supposed.