Tracking down water leaks

Munich, Germany - Researchers in Germany and Italy have developed a sensor to detect the up to 40% of fresh water that seeps out into the ground through cracks and fisures in water supply systems. These leaks from aging pipework go undetected as standard high-end flow sensors - costing up to Euro2000 - are too expensive to be used throughout entire networks.

To address this problem, Acque SpA, the water supply company for Pisa, Italy, engaged the Fraunhofer Institute for Silicon Technology ISIT in Itzehoe, Germany, and Italian firm Sensordynamics to develop a cost effective sensors. The work has led to development of silicon-based probes that only cost around 5% of the the high-end versions and operate on the same principle as mass air flow sensors for measuring the air intake in car engines.

The sensors feature two heating wires mounted one behind the other on a thin membrane. An electric current flowing through the wires heats them to a constant temperature. When cold water flows past them, the front wire gives off more heat into the water than the rear one, which is in its slipstream.

A higher current has to flow through the front wire in order to keep the temperature constant. On the basis of this difference in electrical current, it is possible to determine the speed and volume of the water traveling through the pipes. The special feature of this sensor is that it operates in pulse mode.

The wires are not heated constantly, but only for about three seconds per minute, which means that they are cold most of the time. This helps to reduce lime deposits and air bubbles, which could otherwise distort the measurements. The pulsed operation also saves energy and allows the batteries to last much longer.

The first tests were successful, according to the Fraunhofer Institute. The sensors, it said, survived for three months under water without suffering any damage. For further tests, the researchers recently integrated 70 prototypes into Pisa¹s water pipes. These tests will determine their ability to withstand the flow for several months at full operation, while measuring how much water is traveling through the supply pipes and where it is lost.