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Three things to watch when selecting a position sensor

Autonomous driving, advanced driver assistance systems (ADAS), vehicle electrification, and Industry 4.0 designs are pushing sensing devices for a reinvention to more accurately and efficiently determine position either rotationally or linearly. While these position sensors are based on various design architectures and use interfaces ranging from ratiometric analog to PWM to I2C, what are the common issues that design engineers should keep in mind?

This blog outlines three design considerations that commonly apply to both linear and rotary movements in position sensors serving automotive and industrial applications.

Figure 1 Position sensors serve cost-sensitive automotive applications such as powertrain actuators, pedal positioning, fuel level gauges, and transmission systems. Source: Melexis

  1. Programmable output

Position sensor’s programmable features allow design engineers to easily configure parameters such as speed, resolution, and linearization. For instance, in AS5200L sensor IC from ams, the I2C interface bypasses the need for a dedicated programmer and facilitates easy programming of operating parameters via host MCU.

Likewise, Allegro’s 3DMAG sensor enables direct programming by an MCU, and its outputs allow low-voltage programming regardless of the interface: analog, SAE J2716 SENT, PWM, and I2C. The provision of low-voltage programming makes sensor modules inside electronic control units (ECUs) field replaceable.

Figure 2 A wide range of programmable channel trim and linearization options enable designers to easily adjust magnetic circuitry and optimize accuracy and manufacturing efficiency. Source: Allegro Microsystems

  1. Functional safety

Functional safety is imperative in automotive and industrial designs, so position sensors serving these applications must show full adherence to functional safety guidelines. The stringent requirements of safety-critical automotive applications encompass steering, braking, transmission, and throttle systems.

Allegro’s A31315 position sensor—which offers on-chip diagnostic features to ensure reliable and safe operation—supports ASIL-B for single-die and ASIL-D for dual-die packages for system-level integration in accordance with ISO 26262 functional safety standard. Next, the MLX90421 and MLX90422 non-contact position sensors from Melexis support the ASIL-B level via the safety element out of context (SEooC) approach.

  1. EMC testing

Many position sensors promise first-time-right electromagnetic compatibility (EMC) testing, and that leads to quicker design cycles and lower costs. New position sensors offer immunity to stray magnetic fields and thus bypass the need to shield these sensing devices.

Position sensors like Allegro’s A19520 integrate EMC protection capacitors and incorporate a mixed-signal architecture to feature a wide dynamic range of air gap, a distinction of vibration versus rotation, and stray field immunity.

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