A 3D magnetometer detects magnetic field changes for meter tamper detection, contactless controls, position sensing, and other applications.
Melexis has introduced the MLX90391, a low-power 3D magnetometer for cost-sensitive, high-volume applications such as smart utility meters and contactless controls. The sensor can measure magnetic fields up to ±520 mT, allowing it to detect external magnets that could be used to interfere with meter operation.
The device offers four selectable magnetic-field ranges that allows designers to use the same sensor architecture for applications requiring either magnetic-field measurements or detection of higher magnetic fields.
For smart-meter designs, the higher measurement range can be used for magnetic tamper detection. The sensor detects changes in the surrounding magnetic field while consuming little power, making it suitable for meters and other systems that spend much of their operating time in low-power states.
The MLX90391 uses Melexis’ vertical Hall technology and comes in a TSOT23-6L package. It features an I²C-compatible digital interface, along with a pinout intended to support migration from alternative magnetometers. This can allow existing designs to be updated without requiring PCB changes.
The sensor provides 16-bit digital output for magnetic-field and temperature measurements. Designers can select individual magnetic axes, configure an integrated digital filter, and change operating modes during runtime.
For systems that do not need continuous magnetic-field monitoring, the MLX90391 includes three wake-up-on-change/interrupt modes. These allow a microcontroller to remain in a low-power state until the sensor detects a specified magnetic-field change. A data-ready output and externally synchronised measurement capability are also available for systems where sensing needs to be coordinated with an MCU.
The MLX90391 has a 5 nA power-down current, operates from a 1.7 V to 3.6 V supply, and is specified for ambient temperatures from -40 °C to 125 °C.
Beyond utility meters, the magnetometer can be used for contactless position sensing and control functions. Potential applications include rotary and linear controls, smart knobs, liquid-level sensing, electronic locks, handheld tool triggers, gaming controls, and e-bike gear-position sensing.
Such applications can use magnetic sensing in place of mechanical switches, sliders, or potentiometers. This can help avoid mechanical contact and wear while allowing the sensing element to be placed away from the moving control.
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