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Case study

The technology ‘Gray Wheels’ – how it works

Sagentia's patented sensing technology Gray Wheels is the technology behind the breakthrough water meter for Master Meter. AccuLinx is an 8-wheel absolute encoder that does not require batteries to connect water meters to third party Automatic Reading (‘AMR’) systems.

Gray Wheels reads the position of wheels in an odometer. Each of the wheels carries a small conductive target which can interact with a pattern of coils placed between each of the wheels. These coils consist of a transmit coil and a number of receive coils in a special spatial arrangement. The layout is such that no signal is received on the receive coil from a signal on the transmit coil.

However, the presence of the small conductive target over certain areas of the receive coils unbalances this arrangement due to the eddy currents induced in the target and a telltale signal is picked up in the receive coil. At the heart of the technology is a unique code embodied in the pattern of the coils which allows the position of the target, and hence the wheel to be determined.

The encoder system determines the position of the wheel to one of 30 main zones (3 per decimal digit) and the unique design means that many wheels can be stacked side by side without affecting each other or being sensitive to external interferences. While elegant, technically advanced and robust, the embodiment is very simple, low power and low cost. The odometer wheels only have to carry a small metal foil target and the coils can be implemented as a pattern of tracks on a PCB. The electronics are simple as well, requiring only a standard low power micro-controller and some FET switches to multiplex the signals to the various wheels and coils.