30 Water/Wastewater
pipe diameter (the accuracy improves along with an increasing pipe diameter), the pipe geometry upstream and downstream of the flowmeter and the number of ultrasonic measuring paths. Turbulences which result in different flow velocities should be avoided. Inlet and outlet pipe sections should be as straight as possible in the ideal case, without obstructions such as bends, pumps or valves. Dual-path ultrasonic flowmeters feature a reduced sensitivity to such obstructions. The measurements deliver highly repeatable values in the low flow range. The measuring reliability is also higher since the instrument continues to measure should one of the paths fail. In networks corresponding to the above requirements, the accuracy achievable for a dual-path system is typically +/- 0.5 %.
The so-called clamp-on ultrasonic flow measurement, a relatively new and highly successful measuring principle, is appropriate for the Siwa LeakControl complete solution. For the evaluation, SiwaLeak requires high repeatability in the low flow range, where the accuracy is of lesser importance since the evaluation is based on the comparison of data and not on absolute measured values. Sitrans F clamp-on flowmeters can measure a flow velocity of less than 0.03 m/s without any problem, and this corresponds to 0.3 l/s for a pipe of nominal diameter DN100.
The sensors are simple and easy to install and can be retrofitted at any time since the ultrasonic transducers are simply clamped onto the existing pipelines from the outside and send and receive the acoustic signals through the pipe wall. Installation is therefore possible without having to work on the pipeline or interrupt the supply, in contrast to a compound meter or electromagnetic flowmeter (MAG meter). The transducer cables can be shortened by the installation engineer on site as required and the connectors installed.
The patented wide-beam ultrasonic transducers use the pipe wall as a type of loudspeaker in order to optimise the signal/noise ratio and to provide a larger oscillation range. Transducers of this type are thus less sensitive to changes in the liquid medium.
The sensors can be used for almost all pipeline materials, including plastic, concrete or metal and can be flooded or installed underground.
Clamp-on measurements additionally mean that there are no costs for the building of a shaft: the price for the process engineering including purchase and installation of an electromagnetic flowmeter is approximately 40,000 € in Germany for a pipeline of nominal diameter DN200, and even approximately 110,000 € for a pipeline of nominal diameter DN5001). Considerable cost savings can therefore be achieved by using the clamp-on instrumentation.
The advantages of clamp-on flow measurements are quite clear:
• No working on pipes, thus low installation costs as well as simple and fast assembly
• Mounting and dismounting of measuring point possible without high-cost shaft
• No interruption in supply • High repeatability in the low flow range
Figure 2: Siwa LeakControl software application: example of results of flow measurement Left: normal nighttime flow with an average minimum flow rate of ~ 0 l/s Center: occurrence of leak, leak time
Right: normal state following localisation and repair of leak
• No contact with clean drinking water, perfectly hygienic, special drinking water approval unnecessary
• No contact with measured medium, therefore no deposits on the sensor surface.
• Temporary use also possible (mobile measurements) 1) Example calculation
Successful practical applications of the procedure
The efficiency of this procedure is demonstrated by the example of a municipality in Upper Swabia/Germany where the supply network covers approximately 40 kilometers. Following installation of the monitoring system, the municipality could significantly shorten the duration of leakages and reduce the specific water losses by about half.
Another water supplier in Baden-Wuerttemberg primarily wanted to significantly reduce the localisation overhead by using this innovative procedure. On account of the size of the zones, the search for leaks using the existing monitoring solution took far too long. With this procedure and additional flow measuring points, it is now possible to monitor the 120 km long supply network rapidly and simply. Using a few specific valve activations, the area of a possible leak can be exactly localised within a few reaches. The effort for fine localisation is minimal. The customer is highly satisfied with this solution and has achieved his objective.
The example shows that the installation of additional measuring
Meas. Principle Name Type
Pipe diameter effort of Installation
Type of installation Influence on Process
power supply typical accuracy, Measurement uncertainty repeatability approval for custody transfer specifics and other informations Table 1: Technology overview of modern flow measuring processes IET September / October 2012
www.envirotech-online.com
Electromagnetic flow, MAG SITRANS FM MAG8000
Flow- / Water meter, contacting DN25…DN1200
Qmax 17,6m³/h…40700m³/h (MAG5100W DN15…DN2000)
medium to high: depends on size
1 to 4 hours, for big sizes heavy equipment needed cut pipe, direct bury possible (IP68).
stop water flow, extensive pipe work. battery supply,
24V or 230V with battery backup DN50…DN300:
+/- 0,2% +/- 2mm/s (with extended calibration) DN350… DN1200: +/- 0,4% +/- 2mm/s
+/- 0,1% for v > 0,5m/s
DN50 to DN300: OIML R49, PTB type approval and MI001cold water
liner: EPDM, drinking water approval electrode: Hastelloy
10 year battery life time, integrated data logger, statistics, tariff, leak detection
Figure 3: Ultrasonic transducer for clamp-on flow measurement.
points in association with the data obtained from existing zone inlet measurements can significantly facilitate the identification of leaks.
Water suppliers also profit from the solution's flexibility. For example, the measuring equipment present in a zone with 95,500 inhabitants and a network length of 242 kilometers was successfully integrated into the monitoring system and supplemented by new measuring instruments. As a result of the increased amount of flow data, this water supplier can make more reliable statements in the future, especially regarding small water losses.
Ultrasonic flow SITRANS FU SONOKIT Flow- / Water meter, contacting DN100…DN4000 Qn 100m³/h… 144000m³/h medium, approx. 4 Stunden
drill holes and install sensors, direct bury possible (IP68). no stop of water flow, small pipe work.
battery supply, 24V or 230V with battery backup
2-track: <= +/- (0,5… 1,5%) 1-track: <= +/- (1,0…3,0%)
better 0,25% for v > 0,5m/s local approval in some countries
1- or 2-track measurement, 4- track on request
SITRANS FU Clamp On Flow- / Water meter, non contacting DN10…DN9000
low, approx. 10 minutes, portable version available.
clamp on pipe, direct bury possible. no stop of water flow, no pipe work.
24V or 230V, battery backup with SIWA via external buffer battery
<=+/- 0,5…2,0% for v > 0,3m/s +/- 0,0015…0,006m/s for v < 0,3m/s
+/- 0,15% for v > 0,3m/s +/- 0,0005m/s for v < 0,3m/s
no approval
lower meas. limit < 1cm/s, flow sensitivity 0,0003m/s,
patented Wide-Beam Clamp On ultra sonic measurement, 1- or 2- track measurement, 4- track on request
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