Hall Effect Current Sensor

Baolab MEMS-in-CMOS aims at compass

The MEMS structure, a moveable aluminium plate suspended by springs, is constructed using the metal interconnect layers of the CMOS chip by etching away the Inter Metal Dielectric (IMD) using vHF (vapour HF).  When a current passes through the plate, it experiences a force (the Lorentz force) proportional to the surrounding Earth’s magnetic field.  The resulting displacement is measured using capacitive detection between the moveable plate and fixed electrodes around it, sensing the magnetic field in the x, y and z directions with a single NanoEMS chip.   The company claims that is 3-D digital compass matches performance benchmarks for sensitivity, power consumption and package size, but at a dramatically lower cost, than competitor products. The integration with conditioning and processing circuitry means that Baolab has been able to include an auto-calibration routine to maintain consistent accuracy. The company also aims to produce complex hybrid sensors that include gyroscope, accelerometer and compass sensing in a single chip, all made using the Lorentz force sensing principle. "When several devices are integrated onto a single chip to create a multi-sensor device using NanoEMS, the cost savings compared to conventional MEMS become even more significant especially as different sensors require different production processes, unlike NanoEMS," said Doyle in a statement. Engineering samples of the BLBC3-D NanoCompass will be available in 2012 along with an evaluation kit. The compass provides 5-degree heading resolution and 13-bits per axis. The commercial IC will have either an I2C or SPI digital serial interface and a choice of either a 3-mm by 3-mm by 0.9mm 10-pin DFN/0.5-mm pitch package, which provides drop in compatibility with existing solutions, or a 2-mm by 2-mm by 0.75-mm BGA package.

Design News - Features - Hall Effect Finds Niche in Current Sensing

The venerable Hall Effect sensor is gaining popularity these days in electrical current sensing applications, where it is sometimes replacing transformers and shunt resistors. There, it's helping engineers reduce power consumption, save money and eliminate bulk.

It's doing all that because its technology is simple, well-established and inexpensive. The Hall Effect, which refers to the potential difference on opposite sides of an electrical conductor, was discovered in 1879. It has since been used in applications ranging from automotive to industrial control, where it helps sense position, pressure and motion. In those applications, engineers often choose Hall Effect sensor packages because they're virtually immune to dust, dirt and moisture.

In the past few years, however, some vendors have begun to tailor their Hall Effect products for current sensing applications. Those products are finding a niche among engineers who don't want to “roll their own” or customize existing products for those applications.

As a result, suppliers of the current-sensing Hall Effect devices are finding that their products are being snapped up in a new breed of applications.

“We have customers making intelligent power strips who are very excited about ripping out their bulky transformers and replacing them with our current sensors,” says Mike Doogue, director of strategic marketing for Allegro MicroSystems Inc., a maker of sensors and integrated circuits (ICs).

Indeed, Doogue says he's seen Hall Effect sensors replace shunt resistors in a few space-constrained applications and has seen them replace transformers in white goods, industrial motor control and in a variety of automotive applications.

“In many motor control applications, material costs are sending motor prices through the roof,” Doogue says. “If you can make a motor smaller because you eliminate three big current transformers on each phase of the motor, then you can save on material costs.”

Here, we present two Hall Effect products — from Allegro and LEM — that offer solutions to engineers who need current-sensing technology.

“We've put in the extra features for current sensing,” Doogue says, “so the customers don't have to do it themselves.

Hall-effect sensors, theory and applications

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Hall effect devices

(5.83) Note that the output voltage depends neither on the sensitivity of the Hall sensor nor on the non-linearity of the magnetic core. Current sensors ...

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Figure 6.2 Inductive crankshaft sensor and reluctor wheel 6.2.3 Hall effect sensors If a conductor is carrying a current in a transverse magnetic field then ...