How to select position sensors in industrial scenarios
Position sensors, as one of the key sensor devices in the Internet of Things, can convert the position of the measured object into an output signal, providing accurate linear position, rotation, and angular position information. Therefore, selecting the right sensor is crucial in industrial scenarios.
1. Magnetic position sensor
Magnetic position sensors, as one of the most widely used position sensors, have found widespread application in automobiles and motors due to their advantages such as small size and low power consumption. These sensors measure relative displacement by changing magnetic fields, thereby determining changes in angle. The most common form is the Hall effect-based angle position sensor. Angle position detection is ubiquitous in industrial scenarios, such as directional spraying, valve control, and baffle adjustment, providing ample opportunities for these magnetic position sensors to demonstrate their capabilities.
Taking AMS' AS5070 as an example, the AS5070 is a high-resolution angle position sensor based on the Hall effect, which can be used for precise absolute angle measurement. It is available in two versions: the AS5070A with analog output and the AS5070B with digital output. The latter can be programmed as a PWM or SENT output interface. The AS5070 offers 14-bit resolution, which effectively solves the problem of low cost for small angles.
While these magnetic position sensors can be miniaturized and integrated, achieving high accuracy and low power consumption in angle measurement, they are not without their drawbacks. For example, because these magnetic sensors are sensitive to surrounding magnetic materials and magnetic fields, sensor manufacturers incorporate anti-magnetic interference technologies. The AS5070, for instance, uses an architecture consisting of a sensor array and an analog front-end to compensate for external stray magnetic fields, thus eliminating the need for shielding and reducing system costs.
In addition, since most magnetic position sensors use NdFeB permanent magnets, although these sensors are highly reliable, the well-known brittleness of this permanent magnet material also makes them unsuitable for some harsh industrial environments.
2. Ultrasonic sound-based localization
However, for objects unsuitable for direct contact measurement, another solution is to utilize ultrasonic technology. Similar to optical position sensors, ultrasonic position sensors have unique advantages in non-contact position sensing, especially for objects with complex surfaces, colors, or structures that render photoelectric sensors ineffective. Ultrasonic position sensors generate high-frequency sound waves through a transducer, receive the signals reflected from the object, and calculate the distance using the time-of-flight time. This allows for reliable position detection and accurate continuous distance measurement of various shapes and sizes, particularly for liquid level detection within closed containers.
However, while some of these ultrasonic sensors are programmable and possess self-learning capabilities, their adaptability is not particularly strong. Take, for example, their strength in container level monitoring: different container diameters and even different heights can affect measurement accuracy. It's necessary to select a sensor with the correct range, or use a beam tube or IO-Link to adjust the beamwidth, thereby ensuring that the sound does not interfere with the internal workings of the container.
Like other position sensors, ultrasonic position sensors are not suitable for all scenarios. While the acoustic properties bring many advantages to ultrasonic position sensors, they also introduce some limitations. For example, ultrasonic sensors are ineffective in a vacuum environment because sound cannot propagate there. You might say that there aren't many vacuum environments available, but most vacuum environments are in industrial settings, so they must be taken into consideration.
Traditional is not necessarily the worst.
While innovation continues in position sensors, this doesn't mean traditional inductive position sensors like LVDT/RVDT have lost their market. While they are undeniably large and expensive, their accuracy and reliability remain top-notch. Consequently, some manufacturers are beginning to develop new ideas based on the principles of traditional inductive position sensors.
For example, CeleraMotion's IncOder position sensor eliminates the phase interference structure of traditional inductive sensors through PCB technology. Taking the IncOder angle position sensor as an example, this sensor mainly consists of two parts: a stator and a rotor. Once the stator is powered on, the absolute angle between the rotor and the stator can be obtained without any movement between them. Moreover, multi-layer PCBs can integrate multiple sensors together for redundant safety designs.
