Measuring object displacement through position sensors is an essential function of machines. Sensors play a crucial role in the fabrication of equipment used in various industries. In addition to this, sensors are also present in devices used for day to day living. Sensors measure different types of displacement. Some sensors measure linear, rotational, and angular motion.
One way to determine linear movement using a linear sensor is distance measurement. Distance refers to the change in position from one point to another. Aside from measuring different kinds of displacement, the classification of positions sensors is by their working principle.
Among all kinds of position sensors, potentiometers are the most widely used. The mechanism itself is easy to use and cost-effective which makes it ideal for many industrial applications. The basic set-up of a potentiometer consists of a mechanical shaft and wiper. The resistance created by the slider equates to the position change which converts into an electrical signal. Hence, a potentiometer is a resistive type of sensor.
Potentiometers come in a variety of sizes and designs. Linear potentiometers are flat and long where the machine is connected directly into the shaft of the sensor to detect motion.
Linear variable differential transformer (LVDT)
Robustness is one of the qualities of LVDTs which makes them suitable for applications exposed to extreme conditions. LVDTs are not prone to wear and tear due to their frictionless mechanism. An LVDT is inductive similar to the working principle of an AC transformer used for measuring displacement. LVDTs produce accurate readings through their moving core.
An LVDT consists of a hollow tube with three coils inside. A core or armature connected to the machine either slides up and down or moves from side to side inside the LVDT tube. In addition to robustness, other advantages of using an LVDT are high resolution, sensitivity, and environmental sealing.
A rotary encoder resembles a potentiometer, but it is an optical device used in measuring angular position; it then converts this data into analog or digital output. Rotary encoders are non-contact and change mechanical displacement into electrical signals.
Optical encoders operate using the same principle. LED or infra-red light from a source passes through a high-resolution disk containing code patterns. As the disk rotates, photo-detectors scan it to process information and convert it to a digital output. Rotary encoders are either incremental encoders or absolute position encoders.
Inductive proximity sensor
One common type of inductive proximity sensor is an eddy current sensor. Like LVDTs, inductive proximity sensors are also non-contact and use a magnetic field as the sensing mechanism. Proximity sensors are not strictly for displacement measurement but to detect the proximal presence of objects in front of the machine. Inductive proximity sensors can detect metal objects near the sensor head even when there is no physical contact, hence making this sensor ideal for application in wet or dirty environments. These devices are often used in industrial processing as well as in traffic control. Inductive proximity sensors can detect objects coming from one direction. Capacitive proximity sensors or ultrasonic proximity sensors are used to identify non-metallic objects instead.
Published by Harris Scott