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Electronic metering is without question, the only solution to the outdated and unreliable mechanical metering. It has long been implied that an alternative to this failing technology, which never saw any real advances or improvements from the original design, had to be sought. As a result of many factions within the Water Industry trying to change things, it was always going to be the case that many potential options would be put forward.
Unfortunately, the ‘Mechanical Meter Industry’ firstly put forward the façade of electro-mechanical meters, which, even though they are still being produced, they are merely mechanical meters with electronic registers and offer no real solution.
Surprisingly, and despite many attempts, there have only been three main types of truly electronic meters; Electromagnetic, Fluidic Oscillation and Ultrasonic. All of these meter types have used principles first applied elsewhere, and it is fair to state that some have had better transitions to water metering than others.
Electromagnetic metering, arguably the first non-moving part electronic water meter, offers linear accuracy across its range of measurement, often only with a +/- 0.25% error. However, these velocity water meters require, in relation to other electronic meters, large amounts of power to operate, with the result that only now, are there battery powered models available. Nevertheless, this latest positive progression from AC powered meters, still only allows the sophisticated and expensive technology to be applied on a practical basis for larger applications > 2” (50mm).
Fluidic Oscillation type meters developed from petrochemical applications provided the first real domestic and residential meter on a cost effective basis, and initially, paved the way for true retrofit replacement programs of mechanical meters. However, in applying this technology domestically, it has not been without problems and there are still three main issues that are giving this type of meter difficulties in moving forward.
Firstly, and even despite the meter having no moving parts, the method of operation requires a flow chamber that can create relatively large head losses at medium to high flows, causing poor flow performance for the customer. The second issue is attributed again, to the “principle of operation”, in that the electrodes are required to be in contact with the measured substance, in order to detect and record the flow. Issues are created in this process, as the metallic electrodes can corrode, causing leak paths to the electronics, which results in catastrophic failure. The final issue, and one that is already kept relatively quiet is that the meter is prone to recording electrical current within the water at its highest flowrate (Qmax). Whilst the issue can be prevented with a continuity loop placed around the meter, there is still the possibility that it may fail or that it may not be fitted correctly, which means that meters can over record by significant amounts.
The final, fully electronic water meter measuring method was developed from the well established principle of Ultrasonic’s. Initially, and in many meters today, ultrasonic metering utilised the “Doppler” effect principle to measure the velocity of the water, which unfortunately, even though offering several positives, had major limitations for this type of water metering. The Doppler flow meter’s operation is dependent on the physical properties within the measured medium, such as sand or water bubbles. The randomness of the particle’s and water bubble’s distribution in the pipe cross section, results in inaccuracies.
Furthermore, Doppler effect meters are affected by changes in the liquid's sonic velocity and as a result, the meter is also sensitive to changes in density and temperature. These problems make Doppler flow meters unsuitable for anything other than measuring liquid slurries.
Although most of the known ultrasonic meters use the Doppler effect process, there is a second generation or Ultrasonic Meters that offer the best and most accurate principle for water metering, which is known as transit time or time of flight.
These meters have:-
Transit time ultrasonic water meters suffer none of the failings of other electronic water meters, and thus, provides the true and genuine answer to metering.
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