How to achieve fast, precise, and low power position sensing for real-time control
effect sensor with temperature compensation capability can improve system reliability for enclosures used in industrial or outdoor environments. Human interfaces and controls in home appliances, test and measurement equipment, and personal electronics can benefit from the use of all three axes of motion. A sensor can monitor motion in the X and Y planes to identify rotation of a dial and can identify when the dial is pushed by monitoring a large shift in the X and Y magnetic axes. Monitoring the Z-axis enables the system to identify misalignments and send alerts for wear or damage that the dial may need preventative maintenance. Gimbal motor systems in handheld camera stabilizers and drones benefit from the use of 3D Hall effect sensors with selectable magnetic field sensitivity ranges and other programmable parameters to provide angle measurements to an MCU (Figure 4). The MCU continuously adjusts the motor position as needed to stabilize the platform. A sensor that can accurately and precisely measure angles in on and off-axis positions provides mechanical design flexibility. Out-of-plane measurements often cause different magnetic field strengths (gains) and different offsets in different axes, which can cause angle calculation errors. The
Figure 3: Enclosure tamper detection can be implemented with 3D Hall effect sensors to identify unauthorized access. Image source: Texas Instruments
use of a 3D Hall sensor with gain and offset corrections supports flexibility when placing the sensor relative to the magnet, ensuring the most accurate angle calculations.
rate for a single axis. TMAG7273 devices feature low power modes including: 2.3 milliampere (mA) active mode current; 1 microampere (µA) wake-up and sleep mode current, and; 5 nanoampere (nA) sleep mode current. These ICs include four primary functional blocks (Figure 5): ■ The Power Management & Oscillator block includes undervoltage and overvoltage detection, biasing, and oscillators ■ Hall sensors and associated biasing with multiplexers, noise filters, temperature sensing, integrator circuit, and an analog- to-digital converter (ADC) make up the Sensing and Temperature Measurement block ■ The communication control circuitry, electrostatic discharge (ESD) protection, input/output (I/O) functions, and CRC are included in the Interface Block ■ The Digital Core contains diagnostic circuitry for
mandatory and user-enabled diagnostic checks, other housekeeping functions, and an integrated angle calculation engine that provides 360° angular position information for both on-axis and off-axis angle measurements The TMAG5170 devices are delivered in an 8 pin VSSOP package measuring 3.00 x 3.00 millimeters (mm) and are specified over an ambient temperature range of –40 to +150°C. The TMAG5170A1 includes sensitivity ranges of ±25 millitesla (mT), ±50 mT, and ±100 mT, while the TMAG5170A2 supports ±75 mT, ±150 mT, and ±300 mT. The low-power TMAG5273 family uses 6 pin DBV packages measuring 2.90 x 1.60mm and is specified over an ambient temperature range of –40 to +125°C. It’s also offered in two different models; The TMAG5273A1 with sensitivity ranges of ±40 mT and ±80 mT, and the TMAG5273A2
Figure 2: Integrated 3D Hall effect sensors can measure shaft rotation in robots and other Industry 4.0 applications. Image source: Texas Instruments
angle determination.
automatic teller machines (ATMs), enterprise servers and electronic point of sales equipment can use on-axis field measurements to detect intrusions (Figure 3). When the case is opened, the flux density (B) sensed by the 3D Hall effect sensor decreases until it falls below the flux release point (BRP) specification of the Hall switch, at which time the sensor sends out an alert. When the case is closed, the magnetic flux density must be large enough relative to the BRP to prevent false alerts. Since a magnet’s flux density tends to decrease as its temperature increases, the use of a 3D Hall
Industry 4.0 systems such as robots need multi-axis motion sensing to measure the angle of robotic arms, or at each wheel of mobile robots to support navigation and precise movement throughout a facility. Integrated 3D Hall effect sensors are well-suited for these tasks since they are not susceptible to moisture or dirt. Coplanar measurements provide highly accurate magnetic field measurements of rotating shafts (Figure 2).
Flexible 3D Hall effect sensors
Texas instruments offers designers a selection of three-axis linear Hall effect sensors including the TMAG5170 family of high precision 3D linear Hall effect sensors with a 10 megahertz (MHz) serial peripheral interface (SPI) and cyclic redundancy check (CRC), and; The TMAG5273 family of low power linear 3D Hall effect sensors with an I²C interface and CRC. TMAG5170 devices are optimized for fast and accurate position sensing and include: linear measurement total error of ±2.6% (maximum at 25°C); sensitivity temperature drift of ±2.8% (maximum), and; 20 kilosamples per second (Ksps) conversion
Secure enclosures such as electricity and gas meters,
Human interfaces and controls in home appliances, test & measurement equipment, and personal electronics can benefit from the use of all three axes of motion.
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