From the name “position sensor”, anyone can infer that these devices have some relation to movement. To simplify the meaning of a position sensor, it is any mechanism capable of measuring the displacement or movement of an object with regard to its null position. The different types of motion detected by these sensors are linear, rotary, and angular. But this definition is not sufficient to understand how different types of position sensor technology work and their specific applications.
Potentiometers refer to a specific category of sensors that operate using a particular working principle. Whether it is a tilt sensor or a linear sensor, potentiometers rely on a resistive track to detect motion. The resistive track is connected to a wiper which is also attached directly to the object being measured. As the object moves, the wiper moves along with it. This movement causes the resistance on the track to change as well. The motion of the object is proportional to the resistance change created by the track in relation to the wiper position.
Modifications in the resistive track enable the sensor to measure rotary or angular motion according to what is required by the application. One of the main advantages of a potentiometer is the simple assembly and relatively low cost.
There are two configurations for capacitive position sensors:
- Changing the dielectric constant. A capacitive sensor consists of two plates with a dielectric material that is connected to the object or device. The object’s movement will make the plates produce a dielectric constant.
- Changing the overlap between plates. Another configuration for capacitive sensors is connecting the object to only one plate where an area between the two plates overlaps and moves along with the object. The resulting movement will also produce a capacitance change between these two plates.
A magnetostrictive sensor typically consists of a magnet, electronics, and waveguide. This type of position sensor relies on the use of a magnetic field in displacement measurement.
Other common sensor technologies used today include Hall-effect position sensors and optical position sensors. The working principle of each type of position sensor is a defining characteristic which directly impacts essential performance parameters like accuracy, repeatability, reliability, measurement range, and sensitivity to external factors.
Some specific examples of sensor applications include:
- Processing and manufacturing machines
- Medical and laboratory equipment
- Aircraft and military equipment
- Construction equipment
- Automobiles and other vehicular applications
- Machines used in various industries such as mining, utility, and agriculture
The underlying features of modern sensors have not changed in decades, but there are recent advancements in manufacturing and assembly which have paved the way to creating sensors that are more compact, robust, and reliable. Many sensors today which are made using high-grade alloys and metals can withstand harsh environments. Another development in position sensor technology is the development of non-contact sensors which eliminates the wear and tear factor produced by exposure to vibration, dust, and friction. For most industrial-grade machinery, non-contact position sensors such as LVDTS are the preferred sensing technology.