Intelligent building management saves money: by increasing efficiency, saving resources and reducing maintenance costs. Early leakage detection allows to react quickly and reduce damages. The locations of leakage can be narrowed down and the technicians can be sent to the right place.
The basic principle of the measurement is the following: you send an ultrasonic burst once in the direction of water flow and once in the opposite direction and you measure the time-of-flight.
In flow direction the time-of-flight is shorter than in the opposite one, and the difference between the two is proportional to the flow.
Taking into account some non-linear and temperature corrections, the time difference can therefore be used to calculate the flow. v = c² + DIFTOF/(2L) for v << c
Figure 1: Common sensor designs
The design of an ultrasonic water meter capable of leakage detection is quite a challenge. You have to measure time-of-flight in the range 30 to 200 µs with a precision in the picosecond range. Not only achieving such low noise is a challenge. Having a low offset and offset stability in the range is even a bigger one. For DN15 meters with R800 the target is already 12ps error limit. Sciosense flow converters are based on time-to-digital converter technology that perfectly solves the time measurement task. In addition, the analog front-end is designed with special focus on symmetry and reciprocity so that the offset is small and stable over temperature.
Figure 2: Receive signal
ScioSense flow converters manage that challenges: An integrated charge pump allows to fire with up to 17V. Within the amplified received signal they measure multiple zero crossings. This improves the resolution of the total time-of-flight measurement. With the right choice of the zero crossing – not too early to catch stable periods only, not too late to avoid interference effects – the measurement will be as precise and temperature stable as possible.
By means of a split burst option it is possible to detect a phase jump as a marker within the bust and to get a precise absolute ToF even with strong amplitude variations.