Pisa project tracks leaks
28 Jan 2008
Up to 40% of fresh water seeps out into the ground through cracks and fissures in aging water supply systems. These leaks go undetected as standard high-end flow sensors —- costing up to Euro 2,000 — 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 more cost effective sensors. The work has led to development of silicon-based probes that cost around 5% of the high-end versions. They 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 to keep the temperature constant. The difference in electrical current enables the unit to determine the speed and volume of the water travelling through the pipes.
As the sensor operates in pulse mode, the wires are heated for about three seconds per minute, which means that they are cold most of the time. This reduces lime deposits and air bubbles that can distort the measurements. The pulsed operation also saves energy and allows the batteries to last much longer.
The sensors survived initial tests under water for three months without suffering any damage. For further tests, the researchers recently integrated 70 prototypes into Pisa's water pipes to test their ability to withstand the flow for several months at full operation, measuring flow through the supply pipes and where it is lost.
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 more cost effective sensors. The work has led to development of silicon-based probes that cost around 5% of the high-end versions. They 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 to keep the temperature constant. The difference in electrical current enables the unit to determine the speed and volume of the water travelling through the pipes.
As the sensor operates in pulse mode, the wires are heated for about three seconds per minute, which means that they are cold most of the time. This reduces lime deposits and air bubbles that can distort the measurements. The pulsed operation also saves energy and allows the batteries to last much longer.
The sensors survived initial tests under water for three months without suffering any damage. For further tests, the researchers recently integrated 70 prototypes into Pisa's water pipes to test their ability to withstand the flow for several months at full operation, measuring flow through the supply pipes and where it is lost.
