Ams Sensor Line Provides More Accurate Motor Control

July 9, 2014

Terry Costlow

The ams 47 series magnetic position sensors trim parts counts for motor control systems.

The number of electric motors in vehicles is growing steadily as users want more sunroofs, seat adjusters, and other features; while mileage regulations prompt a shift from hydraulic to electric functions. As usage expands, automakers are also asking for more precise control.

Ams AG is responding to these trends with its 47 series family of magnetic position sensors, which feature Dynamic Angle Error Compensation. DAEC reduces the measurement error attributable to propagation delay compared to systems that rely on DSPs or microcontrollers to determine position. The line boasts accuracy down to a maximum ±0.17° angle error (excluding integral non-linearity).

“Propagation delay is a major contributor to errors; the higher the speed, the higher the error rate,” said Heinz Oyrer, Senior Automotive Marketing Manager at ams. “With a motor that goes to 14,500 rpm, the error rate can be around 12%. Correction implemented externally with DSPs or microcontrollers can reduce that down to 1.2%. Our devices bring it close to zero, dropping down to around 0.12%.”

When measurements are handled by the sensor instead of a processor, the DSP or microcontroller can be used for other tasks. The ams 47 series, which currently consists of three sensors, also integrates more components than previous devices, reducing size and simplifying production.

That also makes it easier to fit controller boards onto the motors, Oyrer explained. The ams parts also eliminate the need for shielding from stray magnetic fields.

“Our sensors are immune to stray fields, which is important in areas like engine compartments where there can be a lot of magnetic fields,” Oyrer said. “We use four cells that are based on differential principles, so stray fields can be cancelled out.”

He also noted that the market for motor control devices is growing steadily. The industry is also shifting to brushless dc motors, which offer smaller size and increased efficiency than brushed motors, as many developments create more demand.

“Now there are around 35 motors on the average car, double that on many luxury vehicles,” Oyrer said. “The trend is to add more to provide more features in the cabin and to replace hydraulics with electric motors. Electrified powertrains also play into this trend.”