Water sensor

A new, inexpensive sensor currently being tested in Pisa, Italy, has been designed to locate water leaks from utility company pipes.

The sensor, developed on behalf of Pisa’s water supply company Acque by researchers at the Fraunhofer Institute for Silicon Technology and their Italian colleagues at Sensordynamics, are silicon based and cost around five percent of the average price of their high-end counterparts.

The new probes function according to the same principle as mass air flow sensors, which have been used for some time to measure the air intake in car engines.

At the heart of the sensor are two heating wires, which are 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.  Accordingly, 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. This helps to reduce lime deposits and air bubbles, which could otherwise distort the measurements.  Another advantage of pulsed operation is that it saves energy, and the batteries that power the sensor last much longer.

The first tests were successful: the sensors survived for three months under water without suffering any damage. For further tests, the researchers integrated 70 prototypes into Pisa’s water pipes just a few weeks ago. There, they must withstand the flow for several months at full operation, measuring how much water is traveling through the supply pipes and where it is lost.

If the tests are successful, it's conceivable that the sensors will be mass produced at a rate of 50,000 to 500,000 per year, according ISIT project manager Dr. Peter Lange.