Ultrasonic Flow Meter Accuracy is Verified for Effluent Discharge Application by South West Water

Independent trials verify reliable 0.5% accuracy over variable weather conditions and insolation to satisfy MCERTS requirements
Emerson Process Management has announced verification of reliable accuracy of its Mobrey MSP900FH ultrasonic open channel flow meter for effluent discharge application in trials carried out by SouthWestWater. The trials were carried out over ninemonths to confirm the meter’s 0.5% accuracy over variable weather conditions and insolation effects across
the range of UK weather conditions from winter to summer.
“Our test rig was designed to eliminate all variables that might have affected the readings, other than the weather,” explained Robin Lennox, ICA specialist for SWWater. “We ran the experiment continuously for nine months so as to include data from cold, wintry conditions, hot summer days and everything in between. Our trial was successful, and after analysis of the results we selected the MSP900FH for our MCERTS ultrasonic applications.”
SW Water carried out the trials in an effort to identify a robust, cost-effective, ultrasonic level meter with performance reliable enough for use in flow measurement to MCERTS standards on its 280+ waste water treatment sites. The experiment ran from January to September 2007.
“Our regular verification checks of the ultrasonic levelmeters used in our open channel flow installations were showing markedly different results for different weather conditions,” continued Lennox.
”Discrepancies of as much as 9% were occurring between measurements taken on a cold, cloudy day, and those taken in warm sunshine.”
“In order to meet the MCERTS regulations on effluent discharge, we are looking for a level meter reading with a consistent uncertainty of no more than plus or minus 0.5%,” says Lennox. “This gives an uncertainty of around 3 or 4% on the final flow reading, which when taken with other uncertainties - for example from the flow structure - enables us to meet the MCERTS requirement.”
Designed for use in open channel flow applications, MSP900FH features a pre-wired remote temperature sensor that accurately measures the ultrasonic path temperature and compensates for inaccuracies caused by solar gain – a common problem with conventional transmitters.
Emerson water industry expert PeterWard says: “Open channel flow systems are routinely exposed to variable weather conditions which can affect their accuracy. Organisations which carry out annual calibrations should verify their measurements regularly through the year and in varying weather conditions in order to ensure they are complying with the MCERTS regulations.”
The Mobrey MSP900FH is 24V DC loop powered, supplied in a waterproof housing sealed to IP68. It has both analogue 4-20mA communications and digital HART options built-in, and can be used stand-alone, or as part of a site-wide measurement, control and data acquisition system.