From Hall Sensors to Encoders: 3 Companies Target Industrial Position Monitoring
Position sensors have been trending, especially with the increasing need for them in industrial settings. What new products have companies come up with and how have they advanced monitoring technology?
The areas where position sensors are being used are growing more and more. They are often used in almost every industry, including automotive, power generation, medical, process controls/factory automation, security systems, and military/aerospace.
From there, position sensors tend to be essential for the operation and control (especially closed-loop control) of all types of motors like a brushless DC motor, synchronous reluctance motor (SRM), induction motor, stepper motors, etc.
Depending on the application, the sensor technologies used may vary. When selecting such sensors for an application, some of the primary considerations can consist of linearity, accuracy, resolution, operating temperature, power requirements, isolation, environmental ruggedness, size, and cost.
A magnetoresistive sensor's schematic that shows how it senses the rotor position of a brushless DC motor in an electric power steering application. Image used courtesy of Infineon Technologies
Since there are so many use cases with an extensive range of motor types, various types of methods for position monitoring are Hall-effect sensors, optical encoders, inductive encoders, tachometers, and derivative methods. To be more specific, these may be used in detecting the position in valves, actuators, gear shifters, or motor control. Some position monitoring techniques may either sense the absolute or relative motion of the object.
With so many options available for position monitoring, three recent releases show what different companies are innovating and adapting to achieve their goals.
TDK Adds Active Stray Field Compensation
The first release this article will dive into is from TDK. Expanding TDK's Micronas 3D HAL sensor portfolio, the latest edition of HAC 3930 / 3960 / 3980 features stray-field compensation and is targeted for automotive and industrial applications. Such stray fields are often generated from electric motors or power lines in hybrid or fully electric vehicles.
The company claims that the devices can suppress external magnetic stray fields by using an array of Hall plates. The core technology is based on TDK's patented 3D HAL pixel-cell technology. This technology claims to allow these sensors to measure linear of up to 35 millimeters or angular of 360 degrees of motion, providing the capability of 3D position detection while measuring magnetic flux density Bx, By, Bz.
A block diagram for the HALC 39xy. Image used courtesy of TDK
The company states that with the integrated capacitors, HAC 39xy meets stringent system-level electrostatic discharge (ESD) and electromagnetic compatibility (EMC) requirements and eliminates the need for a PCB, thus reducing the total system size and cost.
The device is targeted for use in applications such as turbocharger actuators, cooling valves, brake stroke position sensing, position detection in the charging connector lock, as well as the transmission system and the chassis.
With increasing demands for the automation and electrification of vehicles, the standards for safety are also pushed upward. It is encouraging to see that these technologies are moving in that direction.
Melexis’s Enhanced Position Sensor IC
Intended for a similar function and application as the HAC 39xy, Melexis recently introduced a competitive offering of non-contact position sensors. These sensors, the MLX90421 and MLX90422, are based on Melexis's proprietary Triaxis high-accuracy magnetic sensing technology. Of which, a single die comes in two package options: SOIC-8 and DMP-4.
Compared to traditional hall sensors that are sensitive to magnetic flux in one direction, Triaxis technology uses an integrated magnetic concentrator that enables measurements of three magnetic flux components (BX, BY, and BZ) in a single IC or integrated circuit.
A diagram of Triaxis’ integrated magnetic concentrator used by Melexis’s position sensors IC. Image used courtesy of Melexis
These position sensor ICs consist of a Triaxis Hall magnetic front end, an analog-to-digital signal conditioner, a digital signal processor for advanced signal processing, and a programmable output stage driver. The MLX90421 provides analog or PWM output, while the MLX90422 offers a Single Edge Nibble Transmission (SENT) output.
The utilization of Triaxis technology for 3D magnetic field sensing. Image used courtesy of Melexis
These new introductions complement Melexis's existing MLX90364/5/6/7 with enhancements leading to higher magnetic field sensitivity, wider operating temperature (Ta = −40 °C to 160 °C), and multiple packaging options with single and dual die. Compared to TDK's HAC 39xy sensors, it is unclear how sensitive is MLX90421/2 against the stray fields. In comparison, the typical current consumption is slightly higher at 8.5 mA from 6 mA.
Despite how Melexis and TDK's releases were Hall-based sensors, Balluff has gone a different direction with a magnetic encoder.
Balluff’s Magnetic Encoder Solution
The final release to be covered in this article is Balluff's magnetic encoder, targeting industrial automation applications, which claims to measure up to 48 meters with a repeat accuracy of <1 μm. Its BML SF2 magnetic safety encoder measures and transmits incremental position information to a connected safety control system using a G interface, an analog signal with 1 Vpp (sin/cos).
Balluff states that this compact device (12 x 13.1 x 35 mm) is easy to integrate and is especially useful when mounting tolerances pose a challenge to high system performance.
The system also supports the "safe incremental value" function and provides the user access to implementing safety functions, such as safe slow speed (SLS) or safe stop 1 (SS1) per EN IEC 61800-5-2.
Balluff’s BML SF2 for position measurement. Image used courtesy of Balluff
Magnetic encoders are robust and cost-effective; however, they have certain limitations, such as a smaller operating temperature range and higher susceptibility to the magnetic field. Compared to TDK's 3D HAL and Melexis's Triaxis devices that have a wide operating temperature range, Balluff's encoder has a temperature range (ambient) of −20 °C to 80 °C.
For a designer choosing a position sensor, it is essential to look at their application's temperature range and the sensors' output interface, sampling speed, package size and ruggedness, linearity, resolution, repeatability, and cost. The technology on which the device is based comes secondary but can often provide better answers in determining a suitable device.
Interested in other new innovations happening with position monitoring? Find out more in the articles down below.