Application background
A water utility operates an extensive drinking water and wastewater network which now comprises 26 member municipalities. It has independently supplied approximately 55 000 consumers (15 000 households and businesses) with drinking water for more than 20 years. The ailing drinking water networks have been undergoing continual improvements and repairs for some time. As a result, the pressure ratios in the supply lines have stabilised and the quality of the drinking water has also improved. Drinking water losses were significantly reduced with gradual renovations. Highly skilled employees and their cautious handling of damages to the pipeline network also played a role.
There are approximately 14 000 meters to measure consumption, including large and domestic water meters. Mechanical impeller flowmeters are currently in use in the extremely remote distribution stations, and not connected to a power supply. The disadvantage of these meters is that they feature a measuring error of 2-5%. They also require significant maintenance. According to a study performed by a renowned bulk supplier, the errors per year could even increase as much as 5%. For this reason, the customer would like to replace all of the mechanical meters used by its member communities with more precise electromagnetic water flowmeters.
The main supply is split into three lines to provide three municipalities with drinking water. Each of the lines is to be fitted with its own flowmeter to replace the mechanical impeller flowmeters used to date. Two of the lines are DN 150 and one line is DN 200.
The challenge is that there is no external power supply available, only measuring devices equipped with their own power source can be used. The life cycle of the battery packs or batteries must be at least one year. The devices must also be maintenance-free. The flow data is sent to the control station via wireless remote transmission to eliminate on-site queries and keep operating costs low. And, because under certain circumstances water may penetrate the distribution stations, the electronic devices used must be flood proof with a minimum protection category of IP67 or, even better, IP68. An additional float switch sends out a signal should any water get in. The low flow rates here are approximately 1-10 cubic metre per hour. Minimal flow velocities in the range of less than 0,1 m/s can also occur. Even with these sometimes very low flow rates (that can occur at night for example) the devices must be capable of measuring with a maximum error of 1,5 %.
For this application, KROHNE supplied three Waterflux 3000 F electromagnetic, battery-operated water meters in the sizes DN 200 and DN 150. The meters are each equipped with two high-performance batteries. The drinking water lines supply small municipalities of 100-300 inhabitants. In order to measure the extremely rapid and non-continuous flow changes, the default setting of the measuring frequency on the meter must be increased. As there is no loop network, only the forward flow must be metered. Two battery operated KGA 42 devices from KROHNE wirelessly transmit the measuring data. (KGA is the acronym for the KROHNE GSM antenna.) Each of the two KGAs is equipped with four digital and two analogue inputs. Of these eight digital inputs, three are for the measuring signals, three for error messages (such as self-monitoring or battery almost dead) and one is for the external float switch that sends out a signal if water gets into the distribution shaft. The four analog inputs are used later to monitor the pressure. Even with the minimal flow rates, the water meters measure with an error of less than 0,5% of the measured value.
The Waterflux meter requires no separate grounding because it comes with a reference electrode as standard. The KGAs used to transmit the measurement data to the control centre are configured onsite by a KROHNE technician via Bluetooth. It is possible to exchange the mechanical impeller flowmeters directly without the need for any conversion.
Customer benefits
The water utility is now in a position to monitor all up-to-the-minute meter readings and flow values for these three municipalities from the control station, and to detect any errors. The visualisation and evaluation software PCWin is used to present the remotely transmitted data. This eliminates all onsite queries. The only time anyone actually has to be on site is to change the battery. This means that operating costs can be considerably reduced over the long term and are then manageable for the operator: for example, operators can take advantage of reasonable flat rates for businesses for SMS data transmission offered by mobile phone providers.
The supply of replacement batteries has been secured over the long term by the manufacturer. The water meters are absolutely wear-proof and maintenance-free. By determining defined levels at specific times, damages and leaks can be detected immediately. For example, deviations from known night flow rates between 2 and 4 am are used to detect leakage in practice. The Waterflux battery capacity is transferred to the measuring station as an alarm message. With the measuring frequency set here, the life cycle is one and a half to two and a half years. The first message is sent one year prior to the end of the battery life and the second message is sent at approx. 1% prior to the life cycle end. The battery life of the KGA 42 is approx. two to four years and its residual life cycle can be read in the measuring station.
The installed Waterflux 3070 meters have a lifetime of up to 25 years and do not have to be replaced prematurely due to wear and tear, which was a significant cost factor with the mechanical water meters previously used.The IFC 070 is a battery- powered electromagnetic signal converter designed for use in combination with the sensor. It is ideal for remote locations in the water industry where no power connection is available, and provides certainty in case of power failure.
The strength of the Waterflux 3070 lies in its unique flow sensor construction with a rectangular reduced cross section and its efficient coil construction. The coils provide a stronger and more homogenous magnetic field, leading to an improved signal to noise ratio. The measurement is therefore independent of the flow profile and measurements are very stable. This results in a very good low flow performance.
Because of the unique flow sensor design, whereby the mean flow velocity and flow profile are optimised within the rectangular and reduced cross section, the additional uncertainty for upstream disturbances is drastically reduced. The water meter can be installed directly after an elbow or reducer in the pipe without straight inlet or outlet lengths. A substantial reduction of inlet and outlet sections means smaller measurement pits. Another major benefit of the rectangular sensor construction is the very low power consumption of the signal converter. It has a long battery lifetime of up to 15 years with two internal batteries and 20 years with an external battery pack.
For more information contact John Alexander, Krohne SA, +27 (0)11 314 1391, [email protected], www.krohne.com
| Tel: | +27 11 314 1391 |
| Email: | [email protected] |
| www: | www.za.krohne.com |
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